spl: Allow performing BSS init early before board_init_f()

On some platform we have sufficient memory available early on to allow
setting up and using a basic BSS prior to entering board_init_f(). Doing
so can for example be used to carry state over to board_init_r() without
having to resort to extending U-Boot's global data structure.

To support such scenarios add a Kconfig option called CONFIG_SPL_EARLY_BSS
to allow moving the initialization of BSS prior to entering board_init_f(),
if enabled. Note that using this option usually should go along with using
CONFIG_SPL_SEPARATE_BSS and configuring BSS to be located in memory
actually available prior to board_init_f().

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>

diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index 30fba20e1babf75d87e3d39c2aef7f7c380f54fb..c74641dcd9b661fa97237d21b62a2b4019214c28 100644 (file)
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -57,6 +57,33 @@
  * For more information see 'Board Initialisation Flow in README.
  */
 
+/*
+ * Macro for clearing BSS during SPL execution. Usually called during the
+ * relocation process for most boards before entering board_init_r(), but
+ * can also be done early before entering board_init_f() on plaforms that
+ * can afford it due to sufficient memory being available early.
+ */
+
+.macro SPL_CLEAR_BSS
+       ldr     r0, =__bss_start        /* this is auto-relocated! */
+
+#ifdef CONFIG_USE_ARCH_MEMSET
+       ldr     r3, =__bss_end          /* this is auto-relocated! */
+       mov     r1, #0x00000000         /* prepare zero to clear BSS */
+
+       subs    r2, r3, r0              /* r2 = memset len */
+       bl      memset
+#else
+       ldr     r1, =__bss_end          /* this is auto-relocated! */
+       mov     r2, #0x00000000         /* prepare zero to clear BSS */
+
+clbss_l:cmp    r0, r1                  /* while not at end of BSS */
+       strlo   r2, [r0]                /* clear 32-bit BSS word */
+       addlo   r0, r0, #4              /* move to next */
+       blo     clbss_l
+#endif
+.endm
+
 /*
  * entry point of crt0 sequence
  */
@@ -82,6 +109,10 @@ ENTRY(_main)
        mov     r9, r0
        bl      board_init_f_init_reserve
 
+#if defined(CONFIG_SPL_EARLY_BSS)
+       SPL_CLEAR_BSS
+#endif
+
        mov     r0, #0
        bl      board_init_f
 
@@ -119,6 +150,11 @@ here:
        bl      c_runtime_cpu_setup     /* we still call old routine here */
 #endif
 #if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
+
+#if !defined(CONFIG_SPL_EARLY_BSS)
+       SPL_CLEAR_BSS
+#endif
+
 # ifdef CONFIG_SPL_BUILD
        /* Use a DRAM stack for the rest of SPL, if requested */
        bl      spl_relocate_stack_gd
@@ -126,23 +162,6 @@ here:
        movne   sp, r0
        movne   r9, r0
 # endif
-       ldr     r0, =__bss_start        /* this is auto-relocated! */
-
-#ifdef CONFIG_USE_ARCH_MEMSET
-       ldr     r3, =__bss_end          /* this is auto-relocated! */
-       mov     r1, #0x00000000         /* prepare zero to clear BSS */
-
-       subs    r2, r3, r0              /* r2 = memset len */
-       bl      memset
-#else
-       ldr     r1, =__bss_end          /* this is auto-relocated! */
-       mov     r2, #0x00000000         /* prepare zero to clear BSS */
-
-clbss_l:cmp    r0, r1                  /* while not at end of BSS */
-       strlo   r2, [r0]                /* clear 32-bit BSS word */
-       addlo   r0, r0, #4              /* move to next */
-       blo     clbss_l
-#endif
 
 #if ! defined(CONFIG_SPL_BUILD)
        bl coloured_LED_init

diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 7122c069b2d218bcbef171541e9d46c0f58a1bb3..5978fb2934325e474de2bab0f21926c834ce1487 100644 (file)
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -248,6 +248,16 @@ config TPL_BANNER_PRINT
          info. Disabling this option could be useful to reduce SPL boot time
          (e.g. approx. 6 ms faster, when output on i.MX6 with 115200 baud).
 
+config SPL_EARLY_BSS
+       depends on ARM && !ARM64
+       bool "Allows initializing BSS early before entering board_init_f"
+       help
+         On some platform we have sufficient memory available early on to
+         allow setting up and using a basic BSS prior to entering
+         board_init_f. Activating this option will also de-activate the
+         clearing of BSS during the SPL relocation process, thus allowing
+         to carry state from board_init_f to board_init_r by way of BSS.
+
 config SPL_DISPLAY_PRINT
        bool "Display a board-specific message in SPL"
        help