efi/gop: Allow specifying mode number on command line

Add the ability to choose a video mode for the selected gop by using a
command-line argument of the form
	video=efifb:mode=<n>
Signed-off-by: NArvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-12-nivedita@alum.mit.eduSigned-off-by: NArd Biesheuvel <ardb@kernel.org>

Documentation/fb/efifb.rst

@@ -2,8 +2,10 @@
 What is efifb?
 ==============
 
-This is a generic EFI platform driver for Intel based Apple computers.
-efifb is only for EFI booted Intel Macs.
+This is a generic EFI platform driver for systems with UEFI firmware. The
+system must be booted via the EFI stub for this to be usable. efifb supports
+both firmware with Graphics Output Protocol (GOP) displays as well as older
+systems with only Universal Graphics Adapter (UGA) displays.
 
 Supported Hardware
 ==================
@@ -12,11 +14,14 @@ Supported Hardware
 - Macbook
 - Macbook Pro 15"/17"
 - MacMini
+- ARM/ARM64/X86 systems with UEFI firmware
 
 How to use it?
 ==============
 
-efifb does not have any kind of autodetection of your machine.
+For UGA displays, efifb does not have any kind of autodetection of your
+machine.
+
 You have to add the following kernel parameters in your elilo.conf::
 
 	Macbook :
@@ -28,6 +33,9 @@ You have to add the following kernel parameters in your elilo.conf::
 	Macbook Pro 17", iMac 20" :
 		video=efifb:i20
 
+For GOP displays, efifb can autodetect the display's resolution and framebuffer
+address, so these should work out of the box without any special parameters.
+
 Accepted options:
 
 ======= ===========================================================
@@ -36,4 +44,10 @@ nowc	Don't map the framebuffer write combined. This can be used
 	when large amounts of console data are written.
 ======= ===========================================================
 
+Options for GOP displays:
+
+mode=n
+        The EFI stub will set the mode of the display to mode number n if
+        possible.
+
 Edgar Hucek <gimli@dark-green.com>

drivers/firmware/efi/libstub/efi-stub-helper.c

@@ -105,6 +105,9 @@ efi_status_t efi_parse_options(char const *cmdline)
 				efi_disable_pci_dma = true;
 			if (parse_option_str(val, "no_disable_early_pci_dma"))
 				efi_disable_pci_dma = false;
+		} else if (!strcmp(param, "video") &&
+			   val && strstarts(val, "efifb:")) {
+			efi_parse_option_graphics(val + strlen("efifb:"));
 		}
 	}
 	efi_bs_call(free_pool, buf);

drivers/firmware/efi/libstub/efistub.h

@@ -666,6 +666,8 @@ efi_status_t efi_relocate_kernel(unsigned long *image_addr,
 
 efi_status_t efi_parse_options(char const *cmdline);
 
+void efi_parse_option_graphics(char *option);
+
 efi_status_t efi_setup_gop(struct screen_info *si, efi_guid_t *proto,
 			   unsigned long size);
 

drivers/firmware/efi/libstub/gop.c

@@ -8,11 +8,115 @@
 #include <linux/bitops.h>
 #include <linux/efi.h>
 #include <linux/screen_info.h>
+#include <linux/string.h>
 #include <asm/efi.h>
 #include <asm/setup.h>
 
 #include "efistub.h"
 
+enum efi_cmdline_option {
+	EFI_CMDLINE_NONE,
+	EFI_CMDLINE_MODE_NUM,
+};
+
+static struct {
+	enum efi_cmdline_option option;
+	u32 mode;
+} cmdline __efistub_global = { .option = EFI_CMDLINE_NONE };
+
+static bool parse_modenum(char *option, char **next)
+{
+	u32 m;
+
+	if (!strstarts(option, "mode="))
+		return false;
+	option += strlen("mode=");
+	m = simple_strtoull(option, &option, 0);
+	if (*option && *option++ != ',')
+		return false;
+	cmdline.option = EFI_CMDLINE_MODE_NUM;
+	cmdline.mode   = m;
+
+	*next = option;
+	return true;
+}
+
+void efi_parse_option_graphics(char *option)
+{
+	while (*option) {
+		if (parse_modenum(option, &option))
+			continue;
+
+		while (*option && *option++ != ',')
+			;
+	}
+}
+
+static u32 choose_mode_modenum(efi_graphics_output_protocol_t *gop)
+{
+	efi_status_t status;
+
+	efi_graphics_output_protocol_mode_t *mode;
+	efi_graphics_output_mode_info_t *info;
+	unsigned long info_size;
+
+	u32 max_mode, cur_mode;
+	int pf;
+
+	mode = efi_table_attr(gop, mode);
+
+	cur_mode = efi_table_attr(mode, mode);
+	if (cmdline.mode == cur_mode)
+		return cur_mode;
+
+	max_mode = efi_table_attr(mode, max_mode);
+	if (cmdline.mode >= max_mode) {
+		efi_printk("Requested mode is invalid\n");
+		return cur_mode;
+	}
+
+	status = efi_call_proto(gop, query_mode, cmdline.mode,
+				&info_size, &info);
+	if (status != EFI_SUCCESS) {
+		efi_printk("Couldn't get mode information\n");
+		return cur_mode;
+	}
+
+	pf = info->pixel_format;
+
+	efi_bs_call(free_pool, info);
+
+	if (pf == PIXEL_BLT_ONLY || pf >= PIXEL_FORMAT_MAX) {
+		efi_printk("Invalid PixelFormat\n");
+		return cur_mode;
+	}
+
+	return cmdline.mode;
+}
+
+static void set_mode(efi_graphics_output_protocol_t *gop)
+{
+	efi_graphics_output_protocol_mode_t *mode;
+	u32 cur_mode, new_mode;
+
+	switch (cmdline.option) {
+	case EFI_CMDLINE_MODE_NUM:
+		new_mode = choose_mode_modenum(gop);
+		break;
+	default:
+		return;
+	}
+
+	mode = efi_table_attr(gop, mode);
+	cur_mode = efi_table_attr(mode, mode);
+
+	if (new_mode == cur_mode)
+		return;
+
+	if (efi_call_proto(gop, set_mode, new_mode) != EFI_SUCCESS)
+		efi_printk("Failed to set requested mode\n");
+}
+
 static void find_bits(u32 mask, u8 *pos, u8 *size)
 {
 	if (!mask) {
@@ -124,6 +228,9 @@ static efi_status_t setup_gop(struct screen_info *si, efi_guid_t *proto,
 	if (!gop)
 		return EFI_NOT_FOUND;
 
+	/* Change mode if requested */
+	set_mode(gop);
+
 	/* EFI framebuffer */
 	mode = efi_table_attr(gop, mode);
 	info = efi_table_attr(mode, info);