device/oprom/realmode: Add vbe return status support as per VBE spec 3.0

Existing coreboot oprom implementation relies on user selected
vesa mode through CONFIG_FRAMEBUFFER_VESA_MODE Kconfig option
and expects that all oprom might support user selected vesa mode.

Take an example:
Enabling AMD external radeon PCIE graphics card on ICLRVP with
default vesa mode 0x118. Unable to get valid X and Y resolution
after executing vbe_get_mode_info() with 0x4118, return data
buffer shows 0x0 resolution. It causes further hang while trying
to draw bmpblk image at depthcharge.

This patch checks for output register AH in all vbe function
(0x3 and 0x4f00/1/2) and die() if returns error.

Change-Id: Iacd2ce468e038a14424f029df3a0adec3e5fa15c
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33737
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/device/oprom/realmode/x86.c

@@ -50,11 +50,11 @@ extern unsigned char __realmode_buffer;
 /* to have a common register file for interrupt handlers */
 X86EMU_sysEnv _X86EMU_env;
 
-void (*realmode_call)(u32 addr, u32 eax, u32 ebx, u32 ecx, u32 edx,
+unsigned int (*realmode_call)(u32 addr, u32 eax, u32 ebx, u32 ecx, u32 edx,
 		u32 esi, u32 edi) asmlinkage;
 
-void (*realmode_interrupt)(u32 intno, u32 eax, u32 ebx, u32 ecx, u32 edx,
+unsigned int (*realmode_interrupt)(u32 intno, u32 eax, u32 ebx, u32 ecx,
-		u32 esi, u32 edi) asmlinkage;
+		u32 edx, u32 esi, u32 edi) asmlinkage;
 
 static void setup_realmode_code(void)
 {
@@ -221,6 +221,46 @@ static int vbe_mode_info_valid(void)
 	return mode_info_valid;
 }
 
+/*
+ * EAX register is used to indicate the completion status upon return from
+ * VBE function in real mode.
+ *
+ * If the VBE function completed successfully then 0x0 is returned in the AH
+ * register. Otherwise the AH register is set with the nature of the failure:
+ *
+ * AH == 0x00: Function call successful
+ * AH == 0x01: Function call failed
+ * AH == 0x02: Function is not supported in the current HW configuration
+ * AH == 0x03: Function call invalid in current video mode
+ *
+ * Return 0 on success else -1 for failure
+ */
+static int vbe_check_for_failure(int ah)
+{
+	int status;
+
+	switch (ah) {
+	case 0x0:
+		status = 0;
+		break;
+	case 1:
+		printk(BIOS_DEBUG, "VBE: Function call failed!\n");
+		status = -1;
+		break;
+	case 2:
+		printk(BIOS_DEBUG, "VBE: Function is not supported!\n");
+		status = -1;
+		break;
+	case 3:
+	default:
+		printk(BIOS_DEBUG, "VBE: Unsupported video mode %x!\n",
+			CONFIG_FRAMEBUFFER_VESA_MODE);
+		status = -1;
+		break;
+	}
+
+	return status;
+}
 static u8 vbe_get_mode_info(vbe_mode_info_t * mi)
 {
 	printk(BIOS_DEBUG, "VBE: Getting information about VESA mode %04x\n",
@@ -228,8 +268,10 @@ static u8 vbe_get_mode_info(vbe_mode_info_t * mi)
 	char *buffer = PTR_TO_REAL_MODE(__realmode_buffer);
 	u16 buffer_seg = (((unsigned long)buffer) >> 4) & 0xff00;
 	u16 buffer_adr = ((unsigned long)buffer) & 0xffff;
-	realmode_interrupt(0x10, VESA_GET_MODE_INFO, 0x0000,
+	X86_EAX = realmode_interrupt(0x10, VESA_GET_MODE_INFO, 0x0000,
 			mi->video_mode, 0x0000, buffer_seg, buffer_adr);
+	if (vbe_check_for_failure(X86_AH))
+		die("\nError: In %s function\n", __func__);
 	memcpy(mi->mode_info_block, buffer, sizeof(mi->mode_info_block));
 	mode_info_valid = 1;
 	return 0;
@@ -242,8 +284,10 @@ static u8 vbe_set_mode(vbe_mode_info_t * mi)
 	mi->video_mode |= (1 << 14);
 	// request clearing of framebuffer
 	mi->video_mode &= ~(1 << 15);
-	realmode_interrupt(0x10, VESA_SET_MODE, mi->video_mode,
+	X86_EAX = realmode_interrupt(0x10, VESA_SET_MODE, mi->video_mode,
 			0x0000, 0x0000, 0x0000, 0x0000);
+	if (vbe_check_for_failure(X86_AH))
+		die("\nError: In %s function\n", __func__);
 	return 0;
 }
 
@@ -286,8 +330,10 @@ void vbe_set_graphics(void)
 void vbe_textmode_console(void)
 {
 	delay(2);
-	realmode_interrupt(0x10, 0x0003, 0x0000, 0x0000,
+	X86_EAX = realmode_interrupt(0x10, 0x0003, 0x0000, 0x0000,
 				0x0000, 0x0000, 0x0000);
+	if (vbe_check_for_failure(X86_AH))
+		die("\nError: In %s function\n", __func__);
 }
 
 int fill_lb_framebuffer(struct lb_framebuffer *framebuffer)

src/device/oprom/realmode/x86.h

@@ -33,11 +33,11 @@ extern unsigned int __idt_handler_size;
 extern unsigned char __realmode_code;
 extern unsigned int __realmode_code_size;
 
-extern void (*realmode_call)(u32 addr, u32 eax, u32 ebx, u32 ecx, u32 edx,
+extern unsigned int (*realmode_call)(u32 addr, u32 eax, u32 ebx, u32 ecx,
-		u32 esi, u32 edi) asmlinkage;
+		u32 edx, u32 esi, u32 edi) asmlinkage;
 
-extern void (*realmode_interrupt)(u32 intno, u32 eax, u32 ebx, u32 ecx, u32 edx,
+extern unsigned int (*realmode_interrupt)(u32 intno, u32 eax, u32 ebx, u32 ecx,
-		u32 esi, u32 edi) asmlinkage;
+		u32 edx, u32 esi, u32 edi) asmlinkage;
 
 #define FAKE_MEMORY_SIZE (1024*1024) // only 1MB
 #define INITIAL_EBDA_SEGMENT 0xF600

src/device/oprom/realmode/x86_asm.S

@@ -43,6 +43,10 @@ __idt_handler_size:
 	.globl __realmode_code
 __realmode_code:
 
+/* Realmode function return. */
+__realmode_ret = RELOCATED(.)
+	.long 0
+
 /* Realmode IDT pointer structure. */
 __realmode_idt = RELOCATED(.)
 	.word 1023	/* 16 bit limit */
@@ -167,6 +171,13 @@ __lcall_instr = RELOCATED(.)
 	.word 0x0000, 0x0000
 	/* ************************************ */
 
+	/*
+	 * Here is end of real mode call and time to go back to protected mode.
+	 * Before that its better to store current eax into some memory address
+	 * so that context persist in protected mode too.
+	*/
+	mov	%eax, __realmode_ret
+
 	/* If we got here, we are just about done.
 	 * Need to get back to protected mode.
 	 */
@@ -196,7 +207,8 @@ __lcall_instr = RELOCATED(.)
 	popa
 
 	/* and exit */
-	// TODO return AX from OPROM call
+	/* return AX from OPROM call */
+	mov	__realmode_ret, %eax
 	ret
 
 	.globl __realmode_interrupt
@@ -291,6 +303,13 @@ __realmode_interrupt:
 __intXX_instr = RELOCATED(.)
 	.byte 0xcd, 0x00 /* This becomes intXX */
 
+	/*
+	 * Here is end of real mode call and time to go back to protected mode.
+	 * Before that its better to store current eax into some memory address
+	 * so that context persist in protected mode too.
+	*/
+	mov	%eax, __realmode_ret
+
 	/* Ok, the job is done, now go back to protected mode coreboot */
 	movl	%cr0, %eax
 	orl	$PE, %eax
@@ -314,6 +333,8 @@ __intXX_instr = RELOCATED(.)
 	movl	__stack, %esp
 	popf
 	popa
+	/* return AX from OPROM call */
+	mov	__realmode_ret, %eax
 	ret
 
 /* This is the 16-bit interrupt entry point called by the IDT stub code.