firmware: sysfb: Move bpp-depth calculation into screen_info helper

Move the calculation of the bits per pixels for screen_info into a
helper function. This will make it available to other callers besides
the firmware code.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250401094056.32904-14-tzimmermann@suse.de

drivers/firmware/sysfb_simplefb.c

@@ -35,36 +35,7 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
 	if (type != VIDEO_TYPE_VLFB && type != VIDEO_TYPE_EFI)
 		return false;
 
-	/*
+	bits_per_pixel = __screen_info_lfb_bits_per_pixel(si);
-	 * The meaning of depth and bpp for direct-color formats is
-	 * inconsistent:
-	 *
-	 *  - DRM format info specifies depth as the number of color
-	 *    bits; including alpha, but not including filler bits.
-	 *  - Linux' EFI platform code computes lfb_depth from the
-	 *    individual color channels, including the reserved bits.
-	 *  - VBE 1.1 defines lfb_depth for XRGB1555 as 16, but later
-	 *    versions use 15.
-	 *  - On the kernel command line, 'bpp' of 32 is usually
-	 *    XRGB8888 including the filler bits, but 15 is XRGB1555
-	 *    not including the filler bit.
-	 *
-	 * It's not easily possible to fix this in struct screen_info,
-	 * as this could break UAPI. The best solution is to compute
-	 * bits_per_pixel from the color bits, reserved bits and
-	 * reported lfb_depth, whichever is highest.  In the loop below,
-	 * ignore simplefb formats with alpha bits, as EFI and VESA
-	 * don't specify alpha channels.
-	 */
-	if (si->lfb_depth > 8) {
-		bits_per_pixel = max(max3(si->red_size + si->red_pos,
-					  si->green_size + si->green_pos,
-					  si->blue_size + si->blue_pos),
-				     si->rsvd_size + si->rsvd_pos);
-		bits_per_pixel = max_t(u32, bits_per_pixel, si->lfb_depth);
-	} else {
-		bits_per_pixel = si->lfb_depth;
-	}
 
 	for (i = 0; i < ARRAY_SIZE(formats); ++i) {
 		const struct simplefb_format *f = &formats[i];

drivers/video/screen_info_generic.c

@@ -144,3 +144,39 @@ ssize_t screen_info_resources(const struct screen_info *si, struct resource *r,
 	return pos - r;
 }
 EXPORT_SYMBOL(screen_info_resources);
+
+/*
+ * The meaning of depth and bpp for direct-color formats is
+ * inconsistent:
+ *
+ *  - DRM format info specifies depth as the number of color
+ *    bits; including alpha, but not including filler bits.
+ *  - Linux' EFI platform code computes lfb_depth from the
+ *    individual color channels, including the reserved bits.
+ *  - VBE 1.1 defines lfb_depth for XRGB1555 as 16, but later
+ *    versions use 15.
+ *  - On the kernel command line, 'bpp' of 32 is usually
+ *    XRGB8888 including the filler bits, but 15 is XRGB1555
+ *    not including the filler bit.
+ *
+ * It is not easily possible to fix this in struct screen_info,
+ * as this could break UAPI. The best solution is to compute
+ * bits_per_pixel from the color bits, reserved bits and
+ * reported lfb_depth, whichever is highest.
+ */
+
+u32 __screen_info_lfb_bits_per_pixel(const struct screen_info *si)
+{
+	u32 bits_per_pixel = si->lfb_depth;
+
+	if (bits_per_pixel > 8) {
+		bits_per_pixel = max(max3(si->red_size + si->red_pos,
+					  si->green_size + si->green_pos,
+					  si->blue_size + si->blue_pos),
+				     si->rsvd_size + si->rsvd_pos);
+		bits_per_pixel = max_t(u32, bits_per_pixel, si->lfb_depth);
+	}
+
+	return bits_per_pixel;
+}
+EXPORT_SYMBOL(__screen_info_lfb_bits_per_pixel);

include/linux/screen_info.h

@@ -128,6 +128,8 @@ static inline unsigned int screen_info_video_type(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);
+
 #if defined(CONFIG_PCI)
 void screen_info_apply_fixups(void);
 struct pci_dev *screen_info_pci_dev(const struct screen_info *si);