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

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Message-ID: <YsE6mZanHLy9LpBd@ravnborg.org>
Date:   Sun, 3 Jul 2022 08:43:37 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        linux-mips@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, list@...ndingux.net,
        Christophe Branchereau <cbranchereau@...il.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] drm/ingenic: Use the highest possible DMA burst size

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.

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@...r.kernel.org>
> Fixes: 90b86fcc47b4 ("DRM: Add KMS driver for the Ingenic JZ47xx SoCs")
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
Acked-by: Sam Ravnborg <sam@...nborg.org>