Re: [PATCH] drm/ingenic: Use the highest possible DMA burst size

Paul Cercueil
2022-07-04T10:11:49Z

Hi Sam,

Le dim., juil. 3 2022 at 08:43:37 +0200, Sam Ravnborg
<sam@ravnborg.org> a écrit :
> Hi Paul,
>
> On Sun, Jul 03, 2022 at 12:07:27AM +0100, Paul Cercueil wrote:
>> Until now, when running at the maximum resolution of 1280x720 at
>> 32bpp
>> on the JZ4770 SoC the output was garbled, the X/Y position of the
>> top-left corner of the framebuffer warping to a random position with
>> the whole image being offset accordingly, every time a new frame was
>> being submitted.
>>
>> This problem can be eliminated by using a bigger burst size for the
>> DMA.
>
> Are there any alignment constraints of the framebuffer that depends on
> the burst size? I am hit by this with some atmel IP - which is why I
> ask.

I verified this, and everything behaves correctly when the source
address is not aligned to the burst size. So I believe in our case the
DMA is smart enough to auto-select the best burst size, up to the
configured value.

Cheers,
-Paul

>
> Patch looks good and is a-b.
>
>>
>> Set in each soc_info structure the maximum burst size supported by
>> the
>> corresponding SoC, and use it in the driver.
>>
>> Set the new value using regmap_update_bits() instead of
>> regmap_set_bits(), since we do want to override the old value of the
>> burst size. (Note that regmap_set_bits() wasn't really valid before
>> for
>> the same reason, but it never seemed to be a problem).
>>
>> Cc: <stable@vger.kernel.org>
>> Fixes: 90b86fcc47b4 ("DRM: Add KMS driver for the Ingenic JZ47xx
>> SoCs")
>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Acked-by: Sam Ravnborg <sam@ravnborg.org>