lib: sbi: give platform choice of using single memregion to cover OpenSBI

By default the OpenSBI itself is covered by 2 memregions for RX/RW
sections. This is required by platforms with Smepmp to enforce
proper permissions in M mode. Note: M-mode only regions can't
have RWX permissions with Smepmp. Platforms with traditional PMPs
won't be able to benefit from it, as both regions are effectively
RWX in M mode, but usually it's harmless to so. Now we provide
these platforms with an option to disable this logic. It saves 1
PMP entry. For platforms really in short of PMPs, it does make a
difference.

Note: Platform requesting single OpenSBI memregion must be using
      traditional (old) PMP. We expect the platform code to do
      the right thing.

Signed-off-by: Bo Gan <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/sbi/sbi_platform.h b/include/sbi/sbi_platform.h
index d75c12de..e65d9877 100644
--- a/include/sbi/sbi_platform.h
+++ b/include/sbi/sbi_platform.h
@@ -76,6 +76,9 @@ struct sbi_platform_operations {
 	/* Check if specified HART is allowed to do cold boot */
 	bool (*cold_boot_allowed)(u32 hartid);
 
+	/* Check if platform requires single firmware region */
+	bool (*single_fw_region)(void);
+
 	/* Platform nascent initialization */
 	int (*nascent_init)(void);
 
@@ -348,6 +351,24 @@ static inline bool sbi_platform_cold_boot_allowed(
 }
 
 /**
+ * Check whether platform requires single firmware region
+ *
+ * Note: Single firmware region only works with legacy PMP because with
+ * Smepmp M-mode only regions can't have RWX permissions.
+ *
+ * @param plat pointer to struct sbi_platform
+ *
+ * @return true if single firmware region required and false otherwise
+ */
+static inline bool sbi_platform_single_fw_region(
+					const struct sbi_platform *plat)
+{
+	if (plat && sbi_platform_ops(plat)->single_fw_region)
+		return sbi_platform_ops(plat)->single_fw_region();
+	return false;
+}
+
+/**
  * Nascent (very early) initialization for current HART
  *
  * NOTE: This function can be used to do very early initialization of