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Add parent_unique_id fields to struct aplic_data for
IMSIC parent linking in MSI mode. Store parent IMSIC unique_id
during FDT parsing of the APLIC node.
Add aplic_is_msi_mode() complementing aplic_is_direct_mode() to
consolidate delivery mode detection. Add APLIC_TARGET_EIID() macro
for packing the EIID field into the TARGET register.
Add parent_unique_id and parent_irq_map fields to struct aplic_data.
parent_unique_id identifies the upstream IMSIC irqchip device resolved
via sbi_irqchip_find_device() during hwirq_setup. parent_irq_map is
a per-source array allocated at cold init time to track the EIID
assigned by the IMSIC for each APLIC source.
Restore aplic_writel_msicfg() and re-introduce MSI address register
programming in aplic_init(), gated on aplic_is_msi_mode(). Set the
DOMAINCFG_DM bit to switch the hardware to MSI delivery mode when
no IDC structures are present.
Add aplic_program_msi_target() to pack hart_index, guest_index, and
EIID into the APLIC_TARGET register. Add aplic_write_msi() as the
sbi_irqchip write_msi callback that extracts EIID and hart_index from
the MSI message and calls aplic_program_msi_target(). Add
aplic_msi_callback() as the MSI receive callback that dispatches to
sbi_irqchip_process_hwirq() on the APLIC chip.
Extend aplic_hwirq_setup() with an MSI path that resolves the parent
IMSIC chip by parent_unique_id, registers an MSI route via
sbi_irqchip_register_msi(), and stores the allocated EIID in
parent_irq_map for the source being configured.
Extend aplic_hwirq_set_affinity() with an MSI path that delegates
affinity reprogramming to the parent IMSIC chip via
sbi_irqchip_set_affinity() using the stored parent_irq_map entry.
Guard warm_init, process_hwirqs, and hwirq_eoi with early returns in
MSI mode as interrupt delivery and acknowledgement are handled by the
IMSIC in that configuration.
Signed-off-by: Oza Pawandeep <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Instead of parsing ISA extensions separately for each hart in the
generic_extensions_init() function, it is better to parse ISA extensions
for all available harts in the cold boot path. Also, this allows us
to remove fdt_isa_bitmap from scratch space and directly initialize
"extensions" in struct sbi_hart_features for each hart.
Signed-off-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Introduce root-regions-inheritance DT property to control
copying of root domain memregions. Support 'all' and 'm-only'
modes, always inheriting firmware and M-only regions; behavior
matches m-only policy when property is absent.
Signed-off-by: Yu-Chien Peter Lin <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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When "boot-hart" is not specified, dom->boot_hartid was left as -1U,
causing domain context switching to fail. Default it to the coldboot
HART to enable SMP boot in multi-domain setups, consistent with how
next-arg1 is handled.
Also update its description in domain_support.md.
Signed-off-by: Yu-Chien Peter Lin <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Add a 32-bit unique ID to plic, aplic, and imsic data which can be
used to differentiate multiple irqchip devices.
Signed-off-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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The check for the address being different from 0 for the UART, PLIC,
APLIC and IMSIC dt nodes is unnnecessary and could skip valid nodes.
Signed-off-by: Victoriano Morales <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Drivers or platforms may create memory regions with the MMIO flag set
that contain S-mode-accessible MMIO devices. This is strictly correct
and should be allowed, along with the existing default case of
S-mode-accessible MMIO devices appearing in non-MMIO memory regions.
When passed SBI_DOMAIN_MMIO, sbi_domain_check_addr() will perform the
correct set of permission checks.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Yu-Chien Peter Lin <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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According to the Device Tree Spec, Chapter 2.3.8 "ranges" [1]:
The parent address size will be determined from the #address-cells
property of the node that defines the parent’s address space.
In fdt_translate_address(), which considered the parent address size
is the child address size, this commit fix the two address sizes
and parsing the address independently.
Signed-off-by: Max Hsu <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Currently, the fdt_parse_aclint_node() does not handle non-contiguous
hartid correctly and returns incorrect first_hartid and hart_count.
This is because the for-loop in fdt_parse_aclint_node() skips a hartid
for which hartindex is not available (aka corresponding CPU DT node
is disabled).
For example, on a platform with 4 HARTs (hartid 0, 1, 2, and 3) where
CPU DT nodes with hartid 0 and 2 are disabled, the fdt_parse_aclint_node()
returns first_hartid = 1 and hart_count = 3 which is incorrect.
To address the above issue, drop the sbi_hartid_to_hartindex() check
from the for-loop of fdt_parse_aclint_node().
Fixes: 5e90e54a1a53 ("lib: utils:Check that hartid is valid")
Reported-by: Maria Mbaye <[email protected]>
Signed-off-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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OpenSBI only parses MSI information of the first next level subdomain
for now, which makes the root domain misconfigured in some case:
1. the msi is not enabled on the first subdomain of the root domain,
but other subdomains enable MSI.
2. the root domain is set as direct mode, but its subdomains enable MSI.
So it is needed to parse all child of the root domain, Otherwise, the
some non-root domains are broken. As the specification says, it is
safe to parse the MSI information of all its subdomain and write the
msiaddrcfg register of the non root domain as they are read only.
Parse the aplic MSI information recursively for all aplic device.
Reviewed-by: Anup Patel <[email protected]>
Signed-off-by: Inochi Amaoto <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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OpenSBI is capable of emulating time CSR through an external timer
for HARTs that don't implement a full Zicntr extension. Let's add
Zicntr extension in the FDT if CSR emulation is active.
This avoids hardcoding the extension in the devicetree, which may
confuse pre-SBI bootloaders.
Signed-off-by: Yao Zi <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Set the scratch allocation alignment to cacheline size specified by
riscv,cbom-block-size in the DTS file to avoid two atomic variables
from the same cache line causing livelock on some platforms. If the
cacheline is not specified, we set it a default value.
Signed-off-by: Raj Vishwanathan <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Reviewed-by: Samuel Holland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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This function has been obsoleted by the fdt_driver library and is no
longer used.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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No need to initialise the nodes to be added to the linked list
Signed-off-by: Xiang W <[email protected]>
Reviewed-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>
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Harts associated with an ACLINT_MSWI need not have sequential hartids.
It is insufficient to use first_hartid and hart_count. To account for
non-sequential hart ids, include the empty hart-ids' generate hart-count.
Signed-off-by: Raj Vishwanathan <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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When matching drivers to DT nodes, always match all drivers against the
first compatible string before considering fallback compatible strings.
This ensures the most specific match is always selected, regardless of
the order of the drivers or match structures, as long as no compatible
string appears in multiple match structures.
Fixes: 1ccc52c427f3 ("lib: utils/fdt: Add helpers for generic driver initialization")
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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This reduces .bss size by 8 KiB, and should reduce overall memory usage
since most platforms will have significantly fewer than 512 entries in
this table. At the same time, it removes the fixed table size limit.
Since the table is only used within fdt_pmu.c, instead of updating the
extern declaration, make the table local to this file.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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If a property value is too small, len will be zero after the division
on the next line, so the property will be ignored. This is the same
behavior as when the length check fails. Furthermore, the first two
length checks were already ineffectual, because each item in those
arrays is 12 bytes long, not 8.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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For driver subsystems that are not tightly integrated into the OpenSBI
init sequence, it is not important that the drivers are initialized in
any particular order. By putting all of these drivers in one array, they
can all be initialized with a single pass through the devicetree. This
saves about 10 ms of boot time on HiFive Unmatched.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Now that all drivers are using the fdt_driver functions for
initialization, this function is unused and can be removed.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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It is possible that hartid may not be sequential and it should not be validated
against SBI_HARTMASK_MAX_BITS. Instead we should check the index of the hartid,
hart index, against SBI_HARTMASK_MAX_BITS.
Signed-off-by: Raj Vishwanathan <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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The domain_support.md documentation states that the enforce permission
bit (BIT[6]) could be set in the "regions" property of a domain
instance DT node. However, this bit is masked in the current
implementation. This patch unmasks the bit to make it configurable
from DT.
Signed-off-by: Chao Du <[email protected]>
Reviewed-by: Xiang W <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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1. Initialize struct imsic_data imsic to 0 at definition to prevent the
use of uninitialized memory, ensuring the variable starts with known
values.
2. Remove the redundant memset call on the "aplic" parameter since the
memory for aplic is allocated using sbi_zalloc() by the caller
irqchip_aplic_cold_init(), which guarantees it is already set to 0.
Signed-off-by: Huang Borong <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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These drivers were merged on an experimental basis without the RPMI
specification being frozen. As a result, they may not be compatible with
the frozen version of the RPMI protocol. Additionally, their devicetree
bindings have not been reviewed and are subject to change. Warn the user
that these drivers make no compatibility guarantees, and that their
behavior and devicetree bindings may change incompatibly in future
versions of OpenSBI.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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It should possible to fixup FDT from any part of OpenSBI so add
fdt_register_general_fixup() which allows dynamic registration of
FDT fixup callbacks.
Signed-off-by: Anup Patel <[email protected]>
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Currently, each driver subsystem contains its own code for matching
drivers against the platform's devicetree blob. This bloats firmware
size because the several FDT scanning loops are almost exact copies of
each other, and is confusing because the loops do have some subtle
differences. Furthermore, the existing match algorithm is inefficient:
it scans the FDT structure separately for each driver in the list. A
faster algorithm scans the FDT blob only once, matching all drivers in
the list for each `compatible` property seen.
Add new helpers implementing this faster algorithm. Since they must
iterate through the list of drivers, the driver structure cannot be
opaque. However, since the driver list is an array of pointers, the
`struct fdt_driver` can be embedded in a subsystem-specific driver
structure if needed. These three helpers cover all existing use cases
for driver initialization within OpenSBI.
An additional benefit of centralized driver initialization is the
consistent use of fdt_node_is_enabled().
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Use sbi_domain_memregion_init() at the time of parsing domains from
FDT so that sbi_domain_memregion_init() is always used for setting
up all memregions.
Signed-off-by: Anup Patel <[email protected]>
Reviewed-by: Samuel Holland <[email protected]>
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This removes redundant hartid to hartindex conversions from four call
sites and provides a net reduction in code size.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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The domain_support.md documentation states that "the HART to domain instance
assignment can be parsed from the device tree using *optional* DT property
opensbi-domain in each CPU DT node". However, the current implementation does
not treat this parameter as optional when determining which HARTs to assign to
a freshly discovered domain from the device tree, causing an effect where every
HART in the system must be explicitly assigned to a domain only if a domain is
specified in the device tree. Instead, this patch simply ignores CPUs that do
not specify a domain, and does not attempt to assign them into the recently
discovered domain.
Signed-off-by: Gregor Haas <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Distinguish between functions which modify the devicetree and those
which only extract information from it. Other than the iterators in
fdt_domain.c, this is a mechanical conversion.
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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missing
The diagram shown below illustrates the boot-flow involving OP-TEE OS
initialization.
(1)-----------+
| U-Boot SPL |
+------------+
|
v
(2)-------------------------------------------------------------+
| OpenSBI (fw_dynamic) |
| (4)------------------------+ |
| | optee dispatcher driver | |
+-----------------+-------^---------|-------+------------------+
M-mode | | |
---------+--[trusted domain]---+----.----+--[untrusted domain]-------
S-mode | (coldboot domain) | | |
v | | v
(3)---------------------------+ |(5)----------------------------+
| OP-TEE OS | | | U-Boot |
+----------------------------+ | +-----------------------------+
| |
| v
|(6)----------------------------+
| | Linux |
| +-----------------------------+
As OP-TEE OS has device-tree node fixups that need to be passed
through to the next boot stages, e.g. the reserved memory node:
reserved-memory {
#address-cells = <2>;
#size-cells = <2>;
ranges;
optee_core@f1000000 {
no-map;
reg = <0x0 0xf1000000 // OP-TEE OS base address
0x0 0x01000000>;
};
<...>
};
Instead of using 0x0 as the default value, allow identical next-arg1
to be used by non-coldboot domain (i.e., untrusted domain) when the
property is not provided.
Also, update the description of next-arg1 property in the document.
Signed-off-by: Yu Chien Peter Lin <[email protected]>
Reviewed-by: Alvin Chang <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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A new property has been added, with an extensive rationale at [1], that
can be used in place of "riscv,isa" to indicate what extensions are
supported by a given platform that is a list of strings rather than a
single string. There are some differences between the new property,
"riscv,isa-extensions" and the incumbent "riscv,isa" - chief among them
for the sake of parsing being the list of strings, as opposed to a
string. Another advantage is strictly defined meanings for each string
in a dt-binding, rather than deriving meaning from RVI standards. This
may likely to some divergence over time, but, at least for now, there's
no relevant differences between the two for an M-Mode program.
Add support for the new property in OpenSBI, prioritising it, before
falling back to the, now deprecated, "riscv,isa" property if it is not
present.
Link: https://lore.kernel.org/all/20230702-eats-scorebook-c951f170d29f@spud/ [1]
Signed-off-by: Conor Dooley <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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During Linux AIA driver review, the APLIC DT property for interrupt
delegation was renamed to "riscv,delegation" so let's use the new DT
property name and fallback to old DT property name if the new DT
property name is not available.
Fixes: 34612193af92 ("lib: utils/irqchip: Add FDT based driver for APLIC")
Signed-off-by: Anup Patel <[email protected]>
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After calling fdt_node_offset_by_compatible() we must check its return
value and not an unrelated value.
Addresses-Coverity-ID: 1584993 Logically dead code
Fixes: 67ce5a763cfb ("platform: generic: Add support for specify coldboot harts in DT")
Signed-off-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Added support for the generic platform to specify the set of coldboot
hart in DT. If not specified in DT, all harts are allowed to coldboot
as before.
The functions related to sbi_hartmask are not available before coldboot,
so I used bitmap, and added a new bitmap_test() function to test whether
a certain bit of the bitmap is set.
Signed-off-by: Cheng Yang <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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The parser will fail if the timer is clint timer and has regname
property. As the regname is only meaningful for aclint, it is more
robust to only check regname for aclint timer.
Fixes: 6112d58 ("lib: utils/fdt: Allow to use reg-names when parsing ACLINT")
Signed-off-by: Inochi Amaoto <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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On platforms with Smepmp, the MMIO regions accessed by M-mode need
to be explicitly marked with M-mode only read/write or shared (both
(M-mode and S-mode) read/write permission.
If the above is not done then runtime PLIC access from M-mode on
platforms with Smepmp will result in access fault when further
results in CPU hotplug not working.
Signed-off-by: Anup Patel <[email protected]>
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Define an array sbi_hart_ext to map extension ID and name , and use it
for ISA parsing and printing out the supported extensions.
Signed-off-by: Yong-Xuan Wang <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Currently, the fdt_parse_aclint_node() follows a fixed order to parse
ACLINT timer. This may cause the undesirable result when the ACLINT
device does not support mtime without adding an empty entry for it in
the DT.
To be robust, make fdt_parse_aclint_node() support "reg-names" property,
so it can parse the DT in an order independent way. For compatibility,
fdt_parse_aclint_node() only use "reg-names" when parsing ACLINT timer,
and will fallback to the old way if "reg-names" property is not found.
Link: https://lore.kernel.org/all/20231114-skedaddle-precinct-66c8897227bb@squawk/
Signed-off-by: Inochi Amaoto <[email protected]>
Reviewed-by: Anup patel <[email protected]>
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The valid entry count is tracking by hw_event_count so there
is no need to check the whole table.
Signed-off-by: Yu Chien Peter Lin <[email protected]>
Reviewed-by: Atish Patra <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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To allow platform override pmu_init() filling the translation table
fdt_pmu_evt_select[] when PMU node doesn't provide such information,
we need to share the table and its entry counter with other .c file.
We also define the structures of PMU property in fdt_helper.h, so we
can initialize the mappings in arrays.
Signed-off-by: Yu Chien Peter Lin <[email protected]>
Reviewed-by: Atish Patra <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Add a Kconfig option to control PMU fixup, so the next
stage software can dump the PMU node including event
mapping information for debugging purposes.
Signed-off-by: Yu Chien Peter Lin <[email protected]>
Reviewed-by: Atish Patra <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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This patch makes the following changes:
- As sbi_platform_pmu_init() returns a negative error code on
failure, let sbi_pmu_init() print out the error code with
sbi_dprintf().
- In order to distinguish the SBI_EFAIL error returned by
sbi_pmu_add_*_counter_map(), return SBI_ENOENT to indicate
that fdt_pmu_setup() failed to locate "riscv,pmu" node, and
generic_pmu_init() ignores such case.
Signed-off-by: Yu Chien Peter Lin <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Reviewed-by: Lad Prabhakar <[email protected]>
Reviewed-by: Atish Patra <[email protected]>
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- Add Zkr as extension in sbi_hart_extensions enum
- Return "zkr" string for Zkr extension from sbi_hart_extension_id2string
Signed-off-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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The define is hard to read. The continue statement does not do what was
intended.
* Remove do {} while (false);
* Change the name to set_multi_letter_ext
- Other local macros are lower case too.
- Refer to the fact that this is only used for multi-letter extensions.
Addresses-Coverity-ID: 1568359 Unexpected control flow
Fixes: d72f5f17478d ("lib: utils: Add detection of Smepmp from ISA string in FDT")
Signed-off-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Xiang W <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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hart_exts == NULL can only occur if offset and node address lead to an
overflow resulting in exactly NULL. As we don't catch other values of
overflow it does not make sense to treat this one as special.
Addresses-Coverity-ID: 1568355 Logically dead code
Addresses-Coverity-ID: 1568358 Logically dead code
Fixes: 6259b2ec2d09 ("lib: utils/fdt: Fix fdt_parse_isa_extensions() implementation")
Signed-off-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Xiang W <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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Currently, the sbi_hartmask is indexed by hartid which puts a
limit on hartid to be less than SBI_HARTMASK_MAX_BITS.
We extend the sbi_hartmask implementation to use hartindex and
support updating sbi_hartmask using hartid. This removes the
limit on hartid and existing code works largely unmodified.
Signed-off-by: Xiang W <[email protected]>
Signed-off-by: Anup Patel <[email protected]>
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Currently, the fdt_parse_isa_extensions() tries to parse the ISA
string once for each HART. This ISA string parsing can fail for
secondary HARTs if the FDT memory is already overwritten by the
supervisor OS.
To tackle this issue, we improve the fdt_parse_isa_extensions()
implementation to pre-parse ISA string for all HARTs during
cold boot.
Fixes: d72f5f17478d ("lib: utils: Add detection of Smepmp from ISA
string in FDT")
Signed-off-by: Anup Patel <[email protected]>
Tested-By: Mayuresh Chitale<[email protected]>
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- Add function to parse ISA string in FDT.
- Set Smepmp feature bit in extensions if "smepmp" string is found in ISA string.
Signed-off-by: Himanshu Chauhan <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
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This reverts commit 6966ad0abe70 ("platform/lib: Allow the OS to map the
regions that are protected by PMP").
It was thought at the time of this commit that allowing the kernel to map
PMP protected regions was safe but it is actually not: for example, the
hibernation process will try to access any linear mapping page and then
will fault on such mapped PMP regions [1]. Another issue is that the
device tree specification [2] states that a !no-map region must be
declared as EfiBootServicesData/Code in the EFI memory map which would make
the PMP protected regions reclaimable by the kernel. And to circumvent
this, RISC-V edk2 diverges from the DT specification to declare those
regions as EfiReserved.
The no-map attribute was removed to allow the kernel to use hugepages
larger than 2MB to map the linear mapping to improve the performance but
actually a recent talk from Mike Rapoport [3] stated that the
performance benefit was marginal.
For all those reasons, let's mark all the PMP protected regions as "no-map".
[1] https://lore.kernel.org/linux-riscv/CAAYs2=gQvkhTeioMmqRDVGjdtNF_vhB+vm_1dHJxPNi75YDQ_Q@mail.gmail.com/
[2] "3.5.4 /reserved-memory and UEFI" https://github.com/devicetree-org/devicetree-specification/releases/download/v0.4-rc1/devicetree-specification-v0.4-rc1.pdf
[3] https://lwn.net/Articles/931406/
Signed-off-by: Alexandre Ghiti <[email protected]>
Reviewed-by: Atish Patra <[email protected]>
Reviewed-by: Xiang W <[email protected]>
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