* [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT
@ 2019-06-25 12:13 Christoph Hellwig
2019-06-26 7:16 ` Manuel Lauss
0 siblings, 1 reply; 3+ messages in thread
From: Christoph Hellwig @ 2019-06-25 12:13 UTC (permalink / raw)
To: Bartlomiej Zolnierkiewicz
Cc: Manuel Lauss, linux-mips, linux-fbdev, linux-kernel
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT
2019-06-25 12:13 [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT Christoph Hellwig
@ 2019-06-26 7:16 ` Manuel Lauss
2019-07-23 15:35 ` Bartlomiej Zolnierkiewicz
0 siblings, 1 reply; 3+ messages in thread
From: Manuel Lauss @ 2019-06-26 7:16 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Bartlomiej Zolnierkiewicz, Linux-MIPS, linux-fbdev, LKML
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>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] au1200fb: don't use DMA_ATTR_NON_CONSISTENT
2019-06-26 7:16 ` Manuel Lauss
@ 2019-07-23 15:35 ` Bartlomiej Zolnierkiewicz
0 siblings, 0 replies; 3+ messages in thread
From: Bartlomiej Zolnierkiewicz @ 2019-07-23 15:35 UTC (permalink / raw)
To: Manuel Lauss, Christoph Hellwig; +Cc: Linux-MIPS, linux-fbdev, LKML
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
^ permalink raw reply [flat|nested] 3+ messages in thread
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