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

[Paul Cercueil]

Hi Sam,

Le dim., juil. 3 2022 at 08:43:37 +0200, Sam Ravnborg 
<sam@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> >  Fixes: 90b86fcc47b4 ("DRM: Add KMS driver for the Ingenic JZ47xx 
> > SoCs")
> >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>