Merge patch series "Relocate U-Boot in the last bank"

Ilias Apalodimas <[email protected]> says:

There was a discussion recently on the mailing lists regarding our
management of memory above ram_top [0]. The tl;dr is that we have two problems.

The first one is that U-Boot always relocates to the top of the first available
bank unless there's special board code to sidestep that. The second is we don't
successfully deal with devices that can only do 32-bit DMA.

This patch series deals with the first problem by adding a Kconfig option
allowing platforms to relocate to the top of the last discovered bank.

It's worth noting that this is easily testable with QEMU

qemu-system-aarch64 -m 8192 -smp 2 -nographic -cpu cortex-a57 \
    -machine virt,secure=off \
    -bios u-boot.bin \
    -device virtio-rng-pci \
    -drive id=os,if=none,file="$image" \
    -device virtio-blk-device,drive=os \
    -object memory-backend-ram,id=ram0,size=4G \
    -object memory-backend-ram,id=ram1,size=4G \
    -numa node,memdev=ram0 \
    -numa node,memdev=ram1

# RELOC_ADDR_TOP not set
Hit any key to stop autoboot: 0
=> bdinfo
[...]
relocaddr   = 0x000000013f66c000
reloc off   = 0x000000013f66c000
[...]
lmb_dump_all:
 memory.count = 0x1
 memory[0]	[0x40000000-0x23fffffff], 0x200000000 bytes, flags: none
 reserved.count = 0x2
 reserved[0]	[0x13d507000-0x13d509fff], 0x3000 bytes, flags: no-notify, no-overwrite
reserved[1]	[0x13d50aff0-0x23fffffff], 0x102af5010 bytes, flags: no-overwrite
devicetree  = board
[...]
TLB addr    = 0x000000013ffe0000
irq_sp      = 0x000000013e50aff0
sp start    = 0x000000013e50aff0
Early malloc usage: e88 / 2000
=>

# RELOC_ADDR_TOP enabled

=> bdinfo
[...]
relocaddr   = 0x000000023f66c000
reloc off   = 0x000000023f66c000
[...]
lmb_dump_all:
 memory.count = 0x1
 memory[0]	[0x40000000-0x23fffffff], 0x200000000 bytes, flags: none
 reserved.count = 0x2
 reserved[0]	[0x23d507000-0x23d509fff], 0x3000 bytes, flags: no-notify, no-overwrite
 reserved[1]	[0x23d50aff0-0x23fffffff], 0x2af5010 bytes, flags: no-overwrite
devicetree  = board
[...]
TLB addr    = 0x000000023ffe0000
irq_sp      = 0x000000023e50aff0
sp start    = 0x000000023e50aff0
Early malloc usage: e88 / 2000
=>

[0] https://lore.kernel.org/u-boot/CAC_iWjKFAzpj3B_MEW7-dnOrcAV-rfkhXXo8Bv0KgLNP2VJxRA@mail.gmail.com/

Link: https://lore.kernel.org/r/[email protected]

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/develop/memory.rst b/doc/develop/memory.rst
index 5177229630d..3da39bb6c66 100644
--- a/doc/develop/memory.rst
+++ b/doc/develop/memory.rst
@@ -111,6 +111,15 @@ U-Boot Proper Flow
       This follows the same as in SPL flow. In board_init_f(), a part of memory
       is reserved at the end of RAM (see reserve_* functions in init_sequence_f)
 
+   #. Relocation address
+
+      By default U-Boot will try to relocate below the 4GiB boundary. If
+      RELOC_ADDR_TOP is enabled U-Boot will look into the dram bank config of
+      gd->dram[] and try to relocate to the highest available bank. Use this
+      with caution as devices that can only DMA below 4GiB will misbehave
+      since their buffers may be allocated above the 32-bit boundary.
+      Boards can override thre relocation address via board_get_usable_ram_top().
+
    #. Code Relocation
 
       relocate_code() is called which relocates U-Boot code from the current