lib/cbmem_console: Add cbmemc_copy_in function

When running in verstage before bootblock, the PSP (ARM co-processor) is
running with limited SRAM. It needs to stash the verstage console data
internally until DRAM is brought up. Once DRAM is brought up the data is
stashed in a "transfer buffer" region. In the current design, we are
using the same region for the transfer buffer and the
preram_cbmem_console region. This has the following downsides:

1) The pre-x86 buffer needs to be large enough to hold all the
   verstage, bootblock and romstage console logs.
2) On AMD platforms, the PSP verstage is signed. Changing the size of
   preram_cbmem_console after the fact will result in a mismatch of the
   transfer buffer between verstage and bootblock.

This CL adds a new method that allows SoC specific code to copy the
CBMEM console in the transfer buffer to the active CBMEM console.

BUG=b:213828947
TEST=Boot guybrush and no longer see
   *** Pre-CBMEM romstage console overflowed, log truncated!

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: Idc0ab8090db740e0d1b3d21d8968f26471f2e930
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61099
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kangheui Won <khwon@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/include/console/cbmem_console.h

@@ -3,6 +3,7 @@
 #define _CONSOLE_CBMEM_CONSOLE_H_
 
 #include <stdint.h>
+#include <stddef.h>
 
 void cbmemc_init(void);
 void cbmemc_tx_byte(unsigned char data);
@@ -19,6 +20,11 @@ static inline void __cbmemc_init(void)	{}
 static inline void __cbmemc_tx_byte(u8 data)	{}
 #endif
 
+/*
+ * Copy an external cbmem_console into the active cbmem_console.
+ */
+void cbmemc_copy_in(void *buffer, size_t size);
+
 void cbmem_dump_console_to_uart(void);
 void cbmem_dump_console(void);
 #endif

src/lib/cbmem_console.c

@@ -139,6 +139,16 @@ static void copy_console_buffer(struct cbmem_console *src_cons_p)
 	src_cons_p->size = 0;
 }
 
+void cbmemc_copy_in(void *buffer, size_t size)
+{
+	struct cbmem_console *previous = (void *)buffer;
+
+	if (!buffer_valid(previous, size))
+		return;
+
+	copy_console_buffer(previous);
+}
+
 static void cbmemc_reinit(int is_recovery)
 {
 	const size_t size = CONFIG_CONSOLE_CBMEM_BUFFER_SIZE;