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

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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>






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