firmware/sysfb: Fix VESA format selection

Some legacy BIOSes report no reserved bits in their 32-bit rgb mode,
breaking the calculation of bits_per_pixel in  commit f35cd3fa7729
("firmware/sysfb: Fix EFI/VESA format selection").  However they report
lfb_depth correctly for those modes.  Keep the computation but
set bits_per_pixel to lfb_depth if the latter is larger.

v2 fixes the warnings from a max3() macro with arguments of different
types;  split the bits_per_pixel assignment to avoid uglyfing the code
with too many typecasts.

v3 fixes space and formatting blips pointed out by Javier, and change
the bit_per_pixel assignment back to a single statement using two casts.

v4 go back to v2 and use max_t()

Signed-off-by: Pierre Asselin <pa@panix.com>
Fixes: f35cd3fa7729 ("firmware/sysfb: Fix EFI/VESA format selection")
Link: https://lore.kernel.org/r/4Psm6B6Lqkz1QXM@panix3.panix.com
Link: https://lore.kernel.org/r/20230412150225.3757223-1-javierm@redhat.com
Tested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230419044834.10816-1-pa@panix.com

diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c
index 82c64cb..74363ed 100644 (file)
--- a/drivers/firmware/sysfb_simplefb.c
+++ b/drivers/firmware/sysfb_simplefb.c
@@ -51,7 +51,8 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
         *
         * 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 here and ignore lfb_depth. In the loop below,
+        * 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.
         */
@@ -60,6 +61,7 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
                                          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;
        }