From: Thomas Haemmerle <[email protected]> The framebuffer is allocated Normal Non-Cacheable (write-combine). After the splash command's memcpy() from a cached shadow buffer into the hardware framebuffer (see gu_screen_blit()), stores may still reside in the CPU write-combine buffer when scanout next fetches -- visible as partial / corrupted rendering at the bottom of the image.
dsb() alone is not sufficient: it orders subsequent instructions against the outstanding writes but doesn't actively drain the WC buffer to memory. A readback of any byte inside the WC region does, since the load cannot complete until prior stores to the buffer have been retired. Wire lcdif_fb_damage to do that readback after each blit. Keep fb_flush bound to lcdif_crtc_atomic_flush so the SHADOW_LOAD_EN re-latch still fires on fb_close / fbtest paths. Suggested-by: Lucas Stach <[email protected]> Signed-off-by: Thomas Haemmerle <[email protected]> --- drivers/video/lcdif_kms.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/video/lcdif_kms.c b/drivers/video/lcdif_kms.c index e3d1985dc9..57ca92b4be 100644 --- a/drivers/video/lcdif_kms.c +++ b/drivers/video/lcdif_kms.c @@ -396,10 +396,17 @@ static void lcdif_disable_fb_controller(struct fb_info *info) lcdif_disable_controller(lcdif); } +static void lcdif_fb_damage(struct fb_info *info, const struct fb_rect *rect) +{ + /* readback drains the write-combine buffer (dsb() doesn't) */ + (void)*(volatile u8 *)info->screen_base; +} + static struct fb_ops lcdif_fb_ops = { .fb_enable = lcdif_enable_fb_controller, .fb_disable = lcdif_disable_fb_controller, .fb_flush = lcdif_crtc_atomic_flush, + .fb_damage = lcdif_fb_damage, }; /* ----------------------------------------------------------------------------- -- 2.43.0
