video: screen_info: Add pixel-format helper for linear framebuffers

Add screen_info_pixel_format(), which converts a screen_info's
information about the color format to struct pixel_format. The encoding
within the screen_info structure is complex and therefore prone to
errors. Later patches will convert callers to use the pixel format.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250714151513.309475-3-tzimmermann@suse.de

diff --git a/drivers/video/screen_info_generic.c b/drivers/video/screen_info_generic.c
index 900e9386ecebdb92a5a8dd9190156529fa68f9c2..763adbba71cb3914409d529ed9eaaade2e86c390 100644 (file)
--- a/drivers/video/screen_info_generic.c
+++ b/drivers/video/screen_info_generic.c
@@ -5,6 +5,8 @@
 #include <linux/screen_info.h>
 #include <linux/string.h>
 
+#include <video/pixel_format.h>
+
 static void resource_init_named(struct resource *r,
                                resource_size_t start, resource_size_t size,
                                const char *name, unsigned int flags)
@@ -180,3 +182,56 @@ u32 __screen_info_lfb_bits_per_pixel(const struct screen_info *si)
        return bits_per_pixel;
 }
 EXPORT_SYMBOL(__screen_info_lfb_bits_per_pixel);
+
+static int __screen_info_lfb_pixel_format(const struct screen_info *si, struct pixel_format *f)
+{
+       u32 bits_per_pixel = __screen_info_lfb_bits_per_pixel(si);
+
+       if (bits_per_pixel > U8_MAX)
+               return -EINVAL;
+
+       f->bits_per_pixel = bits_per_pixel;
+
+       if (si->lfb_depth > 8) {
+               f->indexed = false;
+               f->alpha.offset = 0;
+               f->alpha.length = 0;
+               f->red.offset = si->red_pos;
+               f->red.length = si->red_size;
+               f->green.offset = si->green_pos;
+               f->green.length = si->green_size;
+               f->blue.offset = si->blue_pos;
+               f->blue.length = si->blue_size;
+       } else {
+               f->indexed = true;
+               f->index.offset = 0;
+               f->index.length = si->lfb_depth;
+       }
+
+       return 0;
+}
+
+/**
+ * screen_info_pixel_format - Returns the screen-info format as pixel-format description
+ *
+ * @si: the screen_info
+ * @f: pointer to return pixel-format description
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise.
+ */
+int screen_info_pixel_format(const struct screen_info *si, struct pixel_format *f)
+{
+       unsigned int type = screen_info_video_type(si);
+
+       /* TODO: Add support for additional types as needed. */
+       switch (type) {
+       case VIDEO_TYPE_VLFB:
+       case VIDEO_TYPE_EFI:
+               return __screen_info_lfb_pixel_format(si, f);
+       }
+
+       /* not supported */
+       return -EINVAL;
+}
+EXPORT_SYMBOL(screen_info_pixel_format);

diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h
index 923d68e0767971b355e2db1c6a6ae9bf5b51b605..1690706206e822cc54dc49ead1ee3d19da7d5dfc 100644 (file)
--- a/include/linux/screen_info.h
+++ b/include/linux/screen_info.h
@@ -12,6 +12,7 @@
 #define SCREEN_INFO_MAX_RESOURCES      3
 
 struct pci_dev;
+struct pixel_format;
 struct resource;
 
 static inline bool __screen_info_has_lfb(unsigned int type)
@@ -136,6 +137,7 @@ static inline u32 __screen_info_vesapm_info_base(const struct screen_info *si)
 ssize_t screen_info_resources(const struct screen_info *si, struct resource *r, size_t num);
 
 u32 __screen_info_lfb_bits_per_pixel(const struct screen_info *si);
+int screen_info_pixel_format(const struct screen_info *si, struct pixel_format *f);
 
 #if defined(CONFIG_PCI)
 void screen_info_apply_fixups(void);