libpayload: Add comments on virtual pointers in lib_sysinfo

After another incident related to virtual pointers in lib_sysinfo (and
resulting confusion), I decided to put some comments on the matter into
the code.

Remember, we decided to always use virtual pointers in lib_sysinfo, but
it's not always obvious from the code, that they are.

See also:
425973c libpayload: Always use virtual pointers in struct sysinfo_t
593f577 libpayload: Fix use of virtual pointers in sysinfo

Change-Id: I886c3b1d182cba07f1aab1667e702e2868ad4b68
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: http://review.coreboot.org/2878
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/arch/armv7/coreboot.c

@@ -129,6 +129,7 @@ static void cb_parse_mrc_cache(unsigned char *ptr, struct sysinfo_t *info)
 #ifdef CONFIG_NVRAM
 static void cb_parse_optiontable(void *ptr, struct sysinfo_t *info)
 {
+	/* ptr points to a coreboot table entry and is already virtual */
 	info->option_table = ptr;
 }
 
@@ -144,6 +145,7 @@ static void cb_parse_checksum(void *ptr, struct sysinfo_t *info)
 #ifdef CONFIG_COREBOOT_VIDEO_CONSOLE
 static void cb_parse_framebuffer(void *ptr, struct sysinfo_t *info)
 {
+	/* ptr points to a coreboot table entry and is already virtual */
 	info->framebuffer = ptr;
 }
 #endif

payloads/libpayload/arch/x86/coreboot.c

@@ -137,6 +137,7 @@ static void cb_parse_mrc_cache(unsigned char *ptr, struct sysinfo_t *info)
 #ifdef CONFIG_NVRAM
 static void cb_parse_optiontable(void *ptr, struct sysinfo_t *info)
 {
+	/* ptr points to a coreboot table entry and is already virtual */
 	info->option_table = ptr;
 }
 
@@ -152,6 +153,7 @@ static void cb_parse_checksum(void *ptr, struct sysinfo_t *info)
 #ifdef CONFIG_COREBOOT_VIDEO_CONSOLE
 static void cb_parse_framebuffer(void *ptr, struct sysinfo_t *info)
 {
+	/* ptr points to a coreboot table entry and is already virtual */
 	info->framebuffer = ptr;
 }
 #endif

payloads/libpayload/include/sysinfo.h

@@ -39,6 +39,12 @@
 
 struct cb_serial;
 
+/*
+ * All pointers in here shall be virtual.
+ *
+ * If a relocation happens after the last call to lib_get_sysinfo(),
+ * it is up to the user to call lib_get_sysinfo() again.
+ */
 struct sysinfo_t {
 	unsigned int cpu_khz;
 	struct cb_serial *serial;