1 files changed, 36 insertions, 0 deletions
diff --git a/drivers/video/screen_info_generic.c b/drivers/video/screen_info_generic.c
index 64117c6367ab..900e9386eceb 100644
--- a/drivers/video/screen_info_generic.c
+++ b/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);