[PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT

[PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT

[Christoph Hellwig]

au1200fb allocates DMA memory using DMA_ATTR_NON_CONSISTENT, but never
calls dma_cache_sync to synchronize the memory between the CPU and the
device.  If it was use on a not cache coherent bus that would be fatal,
but as far as I can tell from the naming and the mips platform
implementation it always is used in cache coherent systems.  Remove
the DMA_ATTR_NON_CONSISTENT flag, which is a no-op in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/video/fbdev/au1200fb.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/au1200fb.c b/drivers/video/fbdev/au1200fb.c
index 26caffb02b7e..265d3b45efd0 100644
--- a/drivers/video/fbdev/au1200fb.c
+++ b/drivers/video/fbdev/au1200fb.c
@@ -1234,7 +1234,7 @@ static int au1200fb_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	struct au1200fb_device *fbdev = info->par;
 
 	return dma_mmap_attrs(fbdev->dev, vma, fbdev->fb_mem, fbdev->fb_phys,
-			fbdev->fb_len, DMA_ATTR_NON_CONSISTENT);
+			fbdev->fb_len, 0);
 }
 
 static void set_global(u_int cmd, struct au1200_lcd_global_regs_t *pdata)
@@ -1692,8 +1692,7 @@ static int au1200fb_drv_probe(struct platform_device *dev)
 
 		fbdev->fb_mem = dmam_alloc_attrs(&dev->dev,
 				PAGE_ALIGN(fbdev->fb_len),
-				&fbdev->fb_phys, GFP_KERNEL,
-				DMA_ATTR_NON_CONSISTENT);
+				&fbdev->fb_phys, GFP_KERNEL, 0);
 		if (!fbdev->fb_mem) {
 			print_err("fail to allocate framebuffer (size: %dK))",
 				  fbdev->fb_len / 1024);
-- 
2.20.1

Re: [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT

[Manuel Lauss]

On Tue, Jun 25, 2019 at 2:13 PM Christoph Hellwig <hch@lst.de> wrote:
>
> au1200fb allocates DMA memory using DMA_ATTR_NON_CONSISTENT, but never
> calls dma_cache_sync to synchronize the memory between the CPU and the
> device.  If it was use on a not cache coherent bus that would be fatal,
> but as far as I can tell from the naming and the mips platform
> implementation it always is used in cache coherent systems.  Remove
> the DMA_ATTR_NON_CONSISTENT flag, which is a no-op in that case.

Very early au1200 chips, on which this driver apparently was developed on,
had issues with cache coherency, but this was fixed in a later step,
none of the 3 steppings I have access to exhibit any problems
with this patch applied.

> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-By: Manuel Lauss <manuel.lauss@gmail.com>

Re: [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT

[Bartlomiej Zolnierkiewicz]

On 6/26/19 9:16 AM, Manuel Lauss wrote:
> On Tue, Jun 25, 2019 at 2:13 PM Christoph Hellwig <hch@lst.de> wrote:
>>
>> au1200fb allocates DMA memory using DMA_ATTR_NON_CONSISTENT, but never
>> calls dma_cache_sync to synchronize the memory between the CPU and the
>> device.  If it was use on a not cache coherent bus that would be fatal,
>> but as far as I can tell from the naming and the mips platform
>> implementation it always is used in cache coherent systems.  Remove
>> the DMA_ATTR_NON_CONSISTENT flag, which is a no-op in that case.
> 
> Very early au1200 chips, on which this driver apparently was developed on,
> had issues with cache coherency, but this was fixed in a later step,
> none of the 3 steppings I have access to exhibit any problems
> with this patch applied.
> 
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Acked-By: Manuel Lauss <manuel.lauss@gmail.com>

Patch queued for v5.4, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics