lcd: implement a callback for splashimage

On some architectures certain values of splashimage will lead to a data abort exception. Document the problem, and implement a callback for splashimage to reject such values. Cc: Anatolij Gustschin <agust@denx.de> Cc: Wolfgang Denk <wd@denx.de> Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il> Acked-by: Igor Grinberg <grinberg@compulab.co.il>

lcd: implement a callback for splashimage
On some architectures certain values of splashimage will lead to a data abort exception. Document the problem, and implement a callback for splashimage to reject such values. Cc: Anatolij Gustschin <agust@denx.de> Cc: Wolfgang Denk <wd@denx.de> Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il> Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Nikita Kiryanov · Tom Rini
1 parent 48ec529100
Showing 4 changed files with 71 additions and 0 deletions Side-by-side Diff
README
common/lcd.c
doc/README.displaying-bmps
include/env_callback.h
@@ -1530,6 +1530,17 @@
 		allows for a "silent" boot where a splash screen is
 		loaded very quickly after power-on.
  
+		CONFIG_SPLASHIMAGE_GUARD
+
+		If this option is set, then U-Boot will prevent the environment
+		variable "splashimage" from being set to a problematic address
+		(see README.displaying-bmps and README.arm-unaligned-accesses).
+		This option is useful for targets where, due to alignment
+		restrictions, an improperly aligned BMP image will cause a data
+		abort. If you think you will not have problems with unaligned
+		accesses (for example because your toolchain prevents them)
+		there is no need to set this option.
+
 		CONFIG_SPLASH_SCREEN_ALIGN
  
 		If this option is set the splash image can be freely positioned
@@ -33,6 +33,8 @@
 #include <common.h>
 #include <command.h>
 #include <stdarg.h>
+#include <search.h>
+#include <env_callback.h>
 #include <linux/types.h>
 #include <stdio_dev.h>
 #if defined(CONFIG_POST)
@@ -1098,6 +1100,30 @@
 	return (void *)lcd_base;
 #endif /* CONFIG_LCD_LOGO && !CONFIG_LCD_INFO_BELOW_LOGO */
 }
+
+#ifdef CONFIG_SPLASHIMAGE_GUARD
+static int on_splashimage(const char *name, const char *value, enum env_op op,
+	int flags)
+{
+	ulong addr;
+	int aligned;
+
+	if (op == env_op_delete)
+		return 0;
+
+	addr = simple_strtoul(value, NULL, 16);
+	/* See README.displaying-bmps */
+	aligned = (addr % 4 == 2);
+	if (!aligned) {
+		printf("Invalid splashimage value. Value must be 16 bit aligned, but not 32 bit aligned\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+U_BOOT_ENV_CALLBACK(splashimage, on_splashimage);
+#endif
  
 void lcd_position_cursor(unsigned col, unsigned row)
 {
+If you are experiencing hangups/data-aborts when trying to display a BMP image,
+the following might be relevant to your situation...
+
+Some architectures cannot handle unaligned memory accesses, and an attempt to
+perform one will lead to a data abort. On such architectures it is necessary to
+make sure all data is properly aligned, and in many situations simply choosing
+a 32 bit aligned address is enough to ensure proper alignment. This is not
+always the case when dealing with data that has an internal layout such as a
+BMP image:
+
+BMP images have a header that starts with 2 byte-size fields followed by mostly
+32 bit fields. The packed struct that represents this header can be seen below:
+
+typedef struct bmp_header {
+	/* Header */
+	char signature[2];
+	__u32	file_size;
+	__u32	reserved;
+	__u32	data_offset;
+	... etc
+} __attribute__ ((packed)) bmp_header_t;
+
+When placed in an aligned address such as 0x80a00000, char signature offsets
+the __u32 fields into unaligned addresses (in our example 0x80a00002,
+0x80a00006, and so on...). When these fields are accessed by U-Boot, a 32 bit
+access is generated at a non-32-bit-aligned address, causing a data abort.
+The proper alignment for BMP images is therefore: 32-bit-aligned-address + 2.
@@ -41,6 +41,12 @@
 #define SILENT_CALLBACK
 #endif
  
+#ifdef CONFIG_SPLASHIMAGE_GUARD
+#define SPLASHIMAGE_CALLBACK "splashimage:splashimage,"
+#else
+#define SPLASHIMAGE_CALLBACK
+#endif
+
 /*
  * This list of callback bindings is static, but may be overridden by defining
  * a new association in the ".callbacks" environment variable.
@@ -51,6 +57,7 @@
 	"bootfile:bootfile," \
 	"loadaddr:loadaddr," \
 	SILENT_CALLBACK \
+	SPLASHIMAGE_CALLBACK \
 	"stdin:console,stdout:console,stderr:console," \
 	CONFIG_ENV_CALLBACK_LIST_STATIC
...	...	@@ -1530,6 +1530,17 @@
1530	1530	allows for a "silent" boot where a splash screen is
1531	1531	loaded very quickly after power-on.
1532	1532
	1533	+ CONFIG_SPLASHIMAGE_GUARD
	1534	+
	1535	+ If this option is set, then U-Boot will prevent the environment
	1536	+ variable "splashimage" from being set to a problematic address
	1537	+ (see README.displaying-bmps and README.arm-unaligned-accesses).
	1538	+ This option is useful for targets where, due to alignment
	1539	+ restrictions, an improperly aligned BMP image will cause a data
	1540	+ abort. If you think you will not have problems with unaligned
	1541	+ accesses (for example because your toolchain prevents them)
	1542	+ there is no need to set this option.
	1543	+
1533	1544	CONFIG_SPLASH_SCREEN_ALIGN
1534	1545
1535	1546	If this option is set the splash image can be freely positioned
...	...	@@ -33,6 +33,8 @@
33	33	#include <common.h>
34	34	#include <command.h>
35	35	#include <stdarg.h>
	36	+#include <search.h>
	37	+#include <env_callback.h>
36	38	#include <linux/types.h>
37	39	#include <stdio_dev.h>
38	40	#if defined(CONFIG_POST)
...	...	@@ -1098,6 +1100,30 @@
1098	1100	return (void *)lcd_base;
1099	1101	#endif /* CONFIG_LCD_LOGO && !CONFIG_LCD_INFO_BELOW_LOGO */
1100	1102	}
	1103	+
	1104	+#ifdef CONFIG_SPLASHIMAGE_GUARD
	1105	+static int on_splashimage(const char name, const char value, enum env_op op,
	1106	+ int flags)
	1107	+{
	1108	+ ulong addr;
	1109	+ int aligned;
	1110	+
	1111	+ if (op == env_op_delete)
	1112	+ return 0;
	1113	+
	1114	+ addr = simple_strtoul(value, NULL, 16);
	1115	+ /* See README.displaying-bmps */
	1116	+ aligned = (addr % 4 == 2);
	1117	+ if (!aligned) {
	1118	+ printf("Invalid splashimage value. Value must be 16 bit aligned, but not 32 bit aligned\n");
	1119	+ return -1;
	1120	+ }
	1121	+
	1122	+ return 0;
	1123	+}
	1124	+
	1125	+U_BOOT_ENV_CALLBACK(splashimage, on_splashimage);
	1126	+#endif
1101	1127
1102	1128	void lcd_position_cursor(unsigned col, unsigned row)
1103	1129	{
	1	+If you are experiencing hangups/data-aborts when trying to display a BMP image,
	2	+the following might be relevant to your situation...
	3	+
	4	+Some architectures cannot handle unaligned memory accesses, and an attempt to
	5	+perform one will lead to a data abort. On such architectures it is necessary to
	6	+make sure all data is properly aligned, and in many situations simply choosing
	7	+a 32 bit aligned address is enough to ensure proper alignment. This is not
	8	+always the case when dealing with data that has an internal layout such as a
	9	+BMP image:
	10	+
	11	+BMP images have a header that starts with 2 byte-size fields followed by mostly
	12	+32 bit fields. The packed struct that represents this header can be seen below:
	13	+
	14	+typedef struct bmp_header {
	15	+ /* Header */
	16	+ char signature[2];
	17	+ __u32 file_size;
	18	+ __u32 reserved;
	19	+ __u32 data_offset;
	20	+ ... etc
	21	+} __attribute__ ((packed)) bmp_header_t;
	22	+
	23	+When placed in an aligned address such as 0x80a00000, char signature offsets
	24	+the __u32 fields into unaligned addresses (in our example 0x80a00002,
	25	+0x80a00006, and so on...). When these fields are accessed by U-Boot, a 32 bit
	26	+access is generated at a non-32-bit-aligned address, causing a data abort.
	27	+The proper alignment for BMP images is therefore: 32-bit-aligned-address + 2.
...	...	@@ -41,6 +41,12 @@
41	41	#define SILENT_CALLBACK
42	42	#endif
43	43
	44	+#ifdef CONFIG_SPLASHIMAGE_GUARD
	45	+#define SPLASHIMAGE_CALLBACK "splashimage:splashimage,"
	46	+#else
	47	+#define SPLASHIMAGE_CALLBACK
	48	+#endif
	49	+
44	50	/*
45	51	* This list of callback bindings is static, but may be overridden by defining
46	52	* a new association in the ".callbacks" environment variable.
...	...	@@ -51,6 +57,7 @@
51	57	"bootfile:bootfile," \
52	58	"loadaddr:loadaddr," \
53	59	SILENT_CALLBACK \
	60	+ SPLASHIMAGE_CALLBACK \
54	61	"stdin:console,stdout:console,stderr:console," \
55	62	CONFIG_ENV_CALLBACK_LIST_STATIC
56	63