configs: stm32mp1: Fix misleading SPL size limitations

A now removed comment promises to "limit SYSRAM usage to first 128 KB".
This would imply that only SYSRAM from 0x2ffc0000 - 0x2ffe0000 would be
used. This is not what happens at all.

First, SPL_MAX_SIZE is referenced from SPL_TEXT_BASE, which on all
existing configs is set to 0x2ffc2500, not SYSRAM_BASE (0x2ffc0000).
Some of it is in the first 128 KiB and some of it is in the second
128 KiB chunk of SYSRAM.

Second, SPL_MAX_SIZE, does not restrict the BSS size. While a valiant
attempt is made via SPL_BSS_MAX_SIZE, the value of 0x00100000 is much
larger than SYSRAM, and doesn't account for the non-BSS sections.

Because we're putting the .text and .bss in the same boat, the correct
way to limit them together is via SPL_MAX_FOOTPRINT. With the current
SPL_TEXT_BASE, we couldn't limit even a very basic SPL to the first
128 KiB, and there is no technical reason to do so. Because of this,
simply allow the SPL to use all SYSRAM.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

include/configs/stm32mp1.h

@@ -50,12 +50,12 @@
 /* SPL support */
 #ifdef CONFIG_SPL
 /* SPL use DDR */
-#define CONFIG_SPL_BSS_MAX_SIZE		0x00100000
 #define CONFIG_SYS_SPL_MALLOC_START	0xC0300000
 #define CONFIG_SYS_SPL_MALLOC_SIZE	0x01D00000
 
-/* limit SYSRAM usage to first 128 KB */
-#define CONFIG_SPL_MAX_SIZE		0x00020000
+/* Restrict SPL to fit within SYSRAM */
+#define STM32_SYSRAM_END		(STM32_SYSRAM_BASE + STM32_SYSRAM_SIZE)
+#define CONFIG_SPL_MAX_FOOTPRINT	(STM32_SYSRAM_END - CONFIG_SPL_TEXT_BASE)
 #define CONFIG_SPL_STACK		(STM32_SYSRAM_BASE + \
 					 STM32_SYSRAM_SIZE)
 #endif /* #ifdef CONFIG_SPL */