[PATCH v6 02/15] efi: bgrt: add accessors for the boot graphics

["Màxim Pedraza Padilla" <maximpedraza@gmail.com>]

The DRM splash client shows the boot graphics the firmware left behind,
and needs the image address and size, its offsets and the status bits.
Reading them from bgrt_tab and bgrt_image_size works with drm_client_lib
built in, but it can be a module, and neither is exported:

  ERROR: modpost: drivers/gpu/drm/clients/drm_client_lib.ko: symbol 'bgrt_tab' undefined!
  ERROR: modpost: drivers/gpu/drm/clients/drm_client_lib.ko: symbol 'bgrt_image_size' undefined!

Rather than export the data, add an accessor for each of them, exported
GPL only, with stubs in efi-bgrt.h for CONFIG_ACPI_BGRT=n so that users
need no #ifdef of their own. The variables stay global for
drivers/acpi/bgrt.c, and are only written by efi_bgrt_init(): mark them
__ro_after_init.

The table gives the image address as a u64. efi_bgrt_has_image() only
says yes when phys_addr_t can hold it, so that it never disagrees with
efi_bgrt_image_address() on kernels with 32-bit physical addresses.

Reported-by: Mario Limonciello <mario.limonciello@amd.com>
Closes: https://lore.kernel.org/dri-devel/5d7067de-97b7-4232-9cf6-e4b978696482@amd.com/
Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Assisted-by: Claude:claude-opus-5-5
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Màxim Pedraza Padilla <maximpedraza@gmail.com>
---
 drivers/firmware/efi/efi-bgrt.c | 75 ++++++++++++++++++++++++++++++++-
 include/linux/efi-bgrt.h        | 39 ++++++++++++++++-
 2 files changed, 111 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/efi-bgrt.c b/drivers/firmware/efi/efi-bgrt.c
index 1da451582812..1affe5528139 100644
--- a/drivers/firmware/efi/efi-bgrt.c
+++ b/drivers/firmware/efi/efi-bgrt.c
@@ -16,8 +16,8 @@
 #include <linux/efi.h>
 #include <linux/efi-bgrt.h>
 
-struct acpi_table_bgrt bgrt_tab;
-size_t bgrt_image_size;
+struct acpi_table_bgrt bgrt_tab __ro_after_init;
+size_t bgrt_image_size __ro_after_init;
 
 struct bmp_header {
 	u16 id;
@@ -89,3 +89,74 @@ void __init efi_bgrt_init(struct acpi_table_header *table)
 out:
 	memset(bgrt, 0, sizeof(bgrt_tab));
 }
+
+/**
+ * efi_bgrt_has_image() - Whether the firmware left a boot graphic
+ *
+ * Return: true if the BGRT points at a BMP image, which efi_bgrt_init()
+ * checked and reserved, at an address that phys_addr_t can hold.
+ */
+bool efi_bgrt_has_image(void)
+{
+	return bgrt_tab.image_address &&
+	       bgrt_tab.image_address == (phys_addr_t)bgrt_tab.image_address;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_has_image);
+
+/**
+ * efi_bgrt_image_address() - Physical address of the boot graphic
+ *
+ * Return: the address of the BMP image, or 0 if there is none.
+ */
+phys_addr_t efi_bgrt_image_address(void)
+{
+	return bgrt_tab.image_address;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_image_address);
+
+/**
+ * efi_bgrt_image_size() - Size of the boot graphic
+ *
+ * Return: the size of the BMP image, as its header gives it, or 0 if there
+ * is none.
+ */
+size_t efi_bgrt_image_size(void)
+{
+	return bgrt_image_size;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_image_size);
+
+/**
+ * efi_bgrt_status() - Status field of the BGRT
+ *
+ * Return: the status byte. Bit 0 tells whether the image is still on
+ * screen and, since ACPI 6.2, bits 1-2 how far it has to be turned to show
+ * upright (ACPI_BGRT_ORIENTATION_OFFSET).
+ */
+u8 efi_bgrt_status(void)
+{
+	return bgrt_tab.status;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_status);
+
+/**
+ * efi_bgrt_image_offset_x() - Horizontal position of the boot graphic
+ *
+ * Return: the X offset, in pixels, at which the firmware drew the image.
+ */
+u32 efi_bgrt_image_offset_x(void)
+{
+	return bgrt_tab.image_offset_x;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_image_offset_x);
+
+/**
+ * efi_bgrt_image_offset_y() - Vertical position of the boot graphic
+ *
+ * Return: the Y offset, in pixels, at which the firmware drew the image.
+ */
+u32 efi_bgrt_image_offset_y(void)
+{
+	return bgrt_tab.image_offset_y;
+}
+EXPORT_SYMBOL_GPL(efi_bgrt_image_offset_y);
diff --git a/include/linux/efi-bgrt.h b/include/linux/efi-bgrt.h
index e6cd51005633..1c287e5fd388 100644
--- a/include/linux/efi-bgrt.h
+++ b/include/linux/efi-bgrt.h
@@ -9,7 +9,14 @@
 void efi_bgrt_init(struct acpi_table_header *table);
 int __init acpi_parse_bgrt(struct acpi_table_header *table);
 
-/* The BGRT data itself; only valid if bgrt_image != NULL. */
+bool efi_bgrt_has_image(void);
+phys_addr_t efi_bgrt_image_address(void);
+size_t efi_bgrt_image_size(void);
+u8 efi_bgrt_status(void);
+u32 efi_bgrt_image_offset_x(void);
+u32 efi_bgrt_image_offset_y(void);
+
+/* The BGRT data itself; only valid if efi_bgrt_has_image(). */
 extern size_t bgrt_image_size;
 extern struct acpi_table_bgrt bgrt_tab;
 
@@ -21,6 +28,36 @@ static inline int __init acpi_parse_bgrt(struct acpi_table_header *table)
 	return 0;
 }
 
+static inline bool efi_bgrt_has_image(void)
+{
+	return false;
+}
+
+static inline phys_addr_t efi_bgrt_image_address(void)
+{
+	return 0;
+}
+
+static inline size_t efi_bgrt_image_size(void)
+{
+	return 0;
+}
+
+static inline u8 efi_bgrt_status(void)
+{
+	return 0;
+}
+
+static inline u32 efi_bgrt_image_offset_x(void)
+{
+	return 0;
+}
+
+static inline u32 efi_bgrt_image_offset_y(void)
+{
+	return 0;
+}
+
 #endif /* !CONFIG_ACPI_BGRT */
 
 #endif /* _LINUX_EFI_BGRT_H */
-- 
2.39.5