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Message-ID: <CAMj1kXFu4=L=ROVAaRORG5HMmYWHb6OXQf6pJ3yAZpeDmfmSeg@mail.gmail.com>
Date: Mon, 24 Nov 2025 18:01:43 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: javierm@...hat.com, arnd@...db.de, richard.lyu@...e.com, x86@...nel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-efi@...r.kernel.org, loongarch@...ts.linux.dev,
linux-riscv@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2 08/10] efi: Support EDID information
On Mon, 24 Nov 2025 at 17:52, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>
> Add LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID to the list of config-table
> UUIDs. Read sysfb_primary_display from the entry. The UUID has been
> generated with uuidgen.
>
> Still support LINUX_EFI_SCREEN_INFO_TABLE_GUID as fallback in case an
> older boot loader invokes the kernel.
>
> If CONFIG_FIRMWARE_EDID=n, EDID information is disabled.
>
> Make the Kconfig symbol CONFIG_FIRMWARE_EDID available with EFI. Setting
> the value to 'n' disables EDID support.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
Why are we adding a new config table again?
> ---
> arch/loongarch/kernel/efi.c | 14 +++++++++++++-
> drivers/firmware/efi/efi-init.c | 14 +++++++++++++-
> drivers/firmware/efi/efi.c | 2 ++
> drivers/video/Kconfig | 8 +++++---
> include/linux/efi.h | 8 +++++---
> 5 files changed, 38 insertions(+), 8 deletions(-)
>
> diff --git a/arch/loongarch/kernel/efi.c b/arch/loongarch/kernel/efi.c
> index 1ef38036e8ae..2d90758e5037 100644
> --- a/arch/loongarch/kernel/efi.c
> +++ b/arch/loongarch/kernel/efi.c
> @@ -72,6 +72,7 @@ bool efi_poweroff_required(void)
> (acpi_gbl_reduced_hardware || acpi_no_s5);
> }
>
> +unsigned long __initdata primary_display_table = EFI_INVALID_TABLE_ADDR;
> unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
>
> #if defined(CONFIG_SYSFB) || defined(CONFIG_EFI_EARLYCON)
> @@ -81,7 +82,18 @@ EXPORT_SYMBOL_GPL(sysfb_primary_display);
>
> static void __init init_primary_display(void)
> {
> - if (screen_info_table == EFI_INVALID_TABLE_ADDR) {
> + if (primary_display_table != EFI_INVALID_TABLE_ADDR) {
> + struct sysfb_display_info *dpy =
> + early_memremap(primary_display_table, sizeof(*dpy));
> +
> + if (!dpy) {
> + pr_err("Could not map primary_display config table\n");
> + return;
> + }
> + sysfb_primary_display = *dpy;
> + memset(dpy, 0, sizeof(*dpy));
> + early_memunmap(dpy, sizeof(*dpy));
> + } else if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
> struct screen_info *si = early_memremap(screen_info_table, sizeof(*si));
>
> if (!si) {
> diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
> index ca697d485116..0f167c0e058e 100644
> --- a/drivers/firmware/efi/efi-init.c
> +++ b/drivers/firmware/efi/efi-init.c
> @@ -23,6 +23,7 @@
>
> #include <asm/efi.h>
>
> +unsigned long __initdata primary_display_table = EFI_INVALID_TABLE_ADDR;
> unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
>
> static int __init is_memory(efi_memory_desc_t *md)
> @@ -67,7 +68,18 @@ EXPORT_SYMBOL_GPL(sysfb_primary_display);
>
> static void __init init_primary_display(void)
> {
> - if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
> + if (primary_display_table != EFI_INVALID_TABLE_ADDR) {
> + struct sysfb_display_info *dpy =
> + early_memremap(primary_display_table, sizeof(*dpy));
> +
> + if (!dpy) {
> + pr_err("Could not map primary_display config table\n");
> + return;
> + }
> + sysfb_primary_display = *dpy;
> + memset(dpy, 0, sizeof(*dpy));
> + early_memunmap(dpy, sizeof(*dpy));
> + } else if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
> struct screen_info *si = early_memremap(screen_info_table, sizeof(*si));
>
> if (!si) {
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index a9070d00b833..c07f0878a4d6 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -63,6 +63,7 @@ static unsigned long __initdata mem_reserve = EFI_INVALID_TABLE_ADDR;
> static unsigned long __initdata rt_prop = EFI_INVALID_TABLE_ADDR;
> static unsigned long __initdata initrd = EFI_INVALID_TABLE_ADDR;
>
> +extern unsigned long primary_display_table;
> extern unsigned long screen_info_table;
>
> struct mm_struct efi_mm = {
> @@ -641,6 +642,7 @@ static const efi_config_table_type_t common_tables[] __initconst = {
> {LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID, &efi.unaccepted, "Unaccepted" },
> #endif
> #ifdef CONFIG_EFI_GENERIC_STUB
> + {LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID, &primary_display_table },
> {LINUX_EFI_SCREEN_INFO_TABLE_GUID, &screen_info_table },
> #endif
> {},
> diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
> index d51777df12d1..f452fac90a9f 100644
> --- a/drivers/video/Kconfig
> +++ b/drivers/video/Kconfig
> @@ -63,11 +63,13 @@ endif # HAS_IOMEM
>
> config FIRMWARE_EDID
> bool "Enable firmware EDID"
> - depends on X86
> + depends on EFI || X86
> help
> This enables access to the EDID transferred from the firmware.
> - On x86, this is from the VESA BIOS. DRM display drivers will
> - be able to export the information to userspace.
> + On EFI systems, the EDID comes from the same device as the
> + primary GOP. On x86 with BIOS, it comes from the VESA BIOS.
> + DRM display drivers will be able to export the information
> + to userspace.
>
> Also enable this if DDC/I2C transfers do not work for your driver
> and if you are using nvidiafb, i810fb or savagefb.
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 2a43094e23f7..f645bcc66ee2 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -406,11 +406,13 @@ void efi_native_runtime_setup(void);
> #define EFI_CC_FINAL_EVENTS_TABLE_GUID EFI_GUID(0xdd4a4648, 0x2de7, 0x4665, 0x96, 0x4d, 0x21, 0xd9, 0xef, 0x5f, 0xb4, 0x46)
>
> /*
> - * This GUID is used to pass to the kernel proper the struct screen_info
> - * structure that was populated by the stub based on the GOP protocol instance
> - * associated with ConOut
> + * These GUIDs are used to pass to the kernel proper the info
> + * structures that were populated by the stub based on the GOP
> + * instance associated with ConOut.
> */
> +#define LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID EFI_GUID(0x8700a405, 0xcda4, 0x46d4, 0xb8, 0xc3, 0x04, 0xe5, 0xcd, 0xb4, 0x30, 0x21)
> #define LINUX_EFI_SCREEN_INFO_TABLE_GUID EFI_GUID(0xe03fc20a, 0x85dc, 0x406e, 0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
> +
> #define LINUX_EFI_ARM_CPU_STATE_TABLE_GUID EFI_GUID(0xef79e4aa, 0x3c3d, 0x4989, 0xb9, 0x02, 0x07, 0xa9, 0x43, 0xe5, 0x50, 0xd2)
> #define LINUX_EFI_LOADER_ENTRY_GUID EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf, 0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
> #define LINUX_EFI_RANDOM_SEED_TABLE_GUID EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2, 0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)
> --
> 2.51.1
>
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