From: Alper Nebi Yasak alpernebiyasak@gmail.com
commit e6acaf25cba14661211bb72181c35dd13b24f5b3 upstream.
The coreboot framebuffer doesn't support transparency, its 'reserved' bit field is merely padding for byte/word alignment of pixel colors [1]. When trying to match the framebuffer to a simplefb format, the kernel driver unnecessarily requires the format's transparency bit field to exactly match this padding, even if the former is zero-width.
Due to a coreboot bug [2] (fixed upstream), some boards misreport the reserved field's size as equal to its position (0x18 for both on a 'Lick' Chromebook), and the driver fails to probe where it would have otherwise worked fine with e.g. the a8r8g8b8 or x8r8g8b8 formats.
Remove the transparency comparison with reserved bits. When the bits-per-pixel and other color components match, transparency will already be in a subset of the reserved field. Not forcing it to match reserved bits allows the driver to work on the boards which misreport the reserved field. It also enables using simplefb formats that don't have transparency bits, although this doesn't currently happen due to format support and ordering in linux/platform_data/simplefb.h.
[1] https://review.coreboot.org/plugins/gitiles/coreboot/+/4.19/src/commonlib/in... [2] https://review.coreboot.org/plugins/gitiles/coreboot/+/4.13/src/drivers/inte...
Signed-off-by: Alper Nebi Yasak alpernebiyasak@gmail.com Link: https://lore.kernel.org/r/20230122190433.195941-1-alpernebiyasak@gmail.com Cc: Salvatore Bonaccorso carnil@debian.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/firmware/google/framebuffer-coreboot.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/drivers/firmware/google/framebuffer-coreboot.c +++ b/drivers/firmware/google/framebuffer-coreboot.c @@ -51,9 +51,7 @@ static int framebuffer_probe(struct core fb->green_mask_pos == formats[i].green.offset && fb->green_mask_size == formats[i].green.length && fb->blue_mask_pos == formats[i].blue.offset && - fb->blue_mask_size == formats[i].blue.length && - fb->reserved_mask_pos == formats[i].transp.offset && - fb->reserved_mask_size == formats[i].transp.length) + fb->blue_mask_size == formats[i].blue.length) pdata.format = formats[i].name; } if (!pdata.format)