[U-Boot] [RFC 06/11] armV7R: K3: am654: Allow using SPL BSS pre-relocation

[Andreas Dannenberg <dannenberg@ti.com>]

In order to be able to use more advanced driver functionality which often
relies on having BSS initialized during early boot prior to relocation
several things need to be in place:

1) Memory needs to be available for BSS to use. For this, we locate BSS
   at the top of the MCU SRAM area, with the stack starting right below
   it,
2) We need to zero-initialize BSS ourselves which will we do during
   board_init_f(),
3) We would also like to skip the implicit zero-initialization as part of
   SPL relocation, so that already initialized variables will carry over
   post-relocation. We will do this with a separate commit by turning on
   the respective CONFIG option.

In this commit we also clean up the assignment of the initial SP address
as part of the refactoring, taking into account the pre-decrement post-
increment nature in which the SP is used on ARM.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
---
 arch/arm/mach-k3/am6_init.c |  7 +++++++
 include/configs/am65x_evm.h | 25 +++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-k3/am6_init.c b/arch/arm/mach-k3/am6_init.c
index 60a580305d..22477efa5b 100644
--- a/arch/arm/mach-k3/am6_init.c
+++ b/arch/arm/mach-k3/am6_init.c
@@ -78,6 +78,13 @@ void board_init_f(ulong dummy)
 
 #ifdef CONFIG_CPU_V7R
 	setup_k3_mpu_regions();
+
+	/*
+	 * When running SPL on R5 we are using SRAM for BSS to have global
+	 * data etc. working prior to relocation. Since this means we need
+	 * to self-manage BSS, clear that section now.
+	 */
+	memset(__bss_start, 0, __bss_end - __bss_start);
 #endif
 
 	/* Init DM early in-order to invoke system controller */
diff --git a/include/configs/am65x_evm.h b/include/configs/am65x_evm.h
index b043bf886b..cff60a8444 100644
--- a/include/configs/am65x_evm.h
+++ b/include/configs/am65x_evm.h
@@ -19,6 +19,29 @@
 #define CONFIG_SYS_SDRAM_BASE1		0x880000000
 
 /* SPL Loader Configuration */
+#ifdef CONFIG_TARGET_AM654_A53_EVM
+#define CONFIG_SYS_INIT_SP_ADDR         (CONFIG_SPL_TEXT_BASE +	\
+					 CONFIG_SYS_K3_NON_SECURE_MSRAM_SIZE)
+#else
+/*
+ * Maximum size in memory allocated to the SPL BSS. Keep it as tight as
+ * possible (to allow the build to go through), as this directly affects
+ * our memory footprint. The less we use for BSS the more we have available
+ * for everything else.
+ */
+#define CONFIG_SPL_BSS_MAX_SIZE		0x5000
+/*
+ * Link BSS to be within SPL in a dedicated region located near the top of
+ * the MCU SRAM, this way making it available also before relocation. Note
+ * that we are not using the actual top of the MCU SRAM as there is a memory
+ * location filled in by the boot ROM that we want to read out without any
+ * interference from the C context.
+ */
+#define CONFIG_SPL_BSS_START_ADDR	(CONFIG_SYS_K3_BOOT_PARAM_TABLE_INDEX -\
+					 CONFIG_SPL_BSS_MAX_SIZE)
+/* Set the stack right below the SPL BSS section */
+#define CONFIG_SYS_INIT_SP_ADDR         CONFIG_SPL_BSS_START_ADDR
+#endif
 
 #ifdef CONFIG_SYS_K3_SPL_ATF
 #define CONFIG_SPL_FS_LOAD_PAYLOAD_NAME	"tispl.bin"
@@ -29,8 +52,6 @@
 #endif
 
 #define CONFIG_SPL_MAX_SIZE		CONFIG_SYS_K3_MAX_DOWNLODABLE_IMAGE_SIZE
-#define CONFIG_SYS_INIT_SP_ADDR         (CONFIG_SPL_TEXT_BASE +	\
-					CONFIG_SYS_K3_NON_SECURE_MSRAM_SIZE - 4)
 
 #define CONFIG_SYS_BOOTM_LEN		SZ_64M
 
-- 
2.17.1