Re: [PATCH] video: mxsfb: Fix framebuffer corruption on mx6sx

On 08/26/2016 04:38 PM, Lucas Stach wrote:

Am Freitag, den 26.08.2016, 16:30 +0200 schrieb Marek Vasut:

quoted

Allocate the framebuffer memory as coherent, otherwise the framebuffer
will suffer from artifacts when displaying scrolling text or video.
This can be replicated on i.MX6SX (armv7), which has more complex memory
architecture compared to the i.MX23/28 (armv5).

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tomi Valkeinen <redacted>
Cc: Fabio Estevam <redacted>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
---
 drivers/video/fbdev/mxsfb.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/mxsfb.c b/drivers/video/fbdev/mxsfb.c
index 4e6608c..bd1a310 100644
--- a/drivers/video/fbdev/mxsfb.c
+++ b/drivers/video/fbdev/mxsfb.c

@@ -800,6 +800,7 @@ static int mxsfb_init_fbinfo(struct mxsfb_info *host,
 			struct fb_videomode *vmode)
 {
 	int ret;
+	struct device *dev = &host->pdev->dev;
 	struct fb_info *fb_info = &host->fb_info;
 	struct fb_var_screeninfo *var = &fb_info->var;
 	dma_addr_t fb_phys;

@@ -825,12 +826,11 @@ static int mxsfb_init_fbinfo(struct mxsfb_info *host,
 
 	/* Memory allocation for framebuffer */
 	fb_size = SZ_2M;
-	fb_virt = alloc_pages_exact(fb_size, GFP_DMA);
+	fb_virt = dma_alloc_coherent(dev, PAGE_ALIGN(fb_size), &fb_phys,
+				     GFP_KERNEL);

You probably want writecombined memory here instead of coherent. Using
coherent memory for framebuffers sucks performance wise.

Ah, true. That'd be dma_{alloc,free}_wc() , right ?

-- 
Best regards,
Marek Vasut