linux-kernel - Re: [PATCH v2] drm: mxsfb: check framebuffer pitch

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Date:   Tue, 8 Sep 2020 15:58:55 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     marex@...x.de, airlied@...ux.ie, daniel@...ll.ch,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, tomi.valkeinen@...com, linux-imx@....com,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: mxsfb: check framebuffer pitch

Hi Stefan,

Thank you for the patch.

On Tue, Sep 08, 2020 at 02:55:58PM +0200, Stefan Agner wrote:
> The lcdif IP does not support a framebuffer pitch (stride) other than
> framebuffer width. Check for equality and reject the framebuffer
> otherwise.
> 
> This prevents a distorted picture when using 640x800 and running the
> Mesa graphics stack. Mesa tires to use a cache aligned stride, which

Still s/tires/tries/ :-)

> leads at that particular resolution to width != stride. Currently
> Mesa has no fallback behavior, but rejecting this configuration allows
> userspace to handle the issue correctly.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index 8c549c3931af..fa6798d21029 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -21,6 +21,7 @@
>  #include <drm/drm_connector.h>
>  #include <drm/drm_drv.h>
>  #include <drm/drm_fb_helper.h>
> +#include <drm/drm_fourcc.h>
>  #include <drm/drm_gem_cma_helper.h>
>  #include <drm/drm_gem_framebuffer_helper.h>
>  #include <drm/drm_irq.h>
> @@ -81,8 +82,26 @@ void mxsfb_disable_axi_clk(struct mxsfb_drm_private *mxsfb)
>  		clk_disable_unprepare(mxsfb->clk_axi);
>  }
>  
> +static struct drm_framebuffer *
> +mxsfb_fb_create(struct drm_device *dev, struct drm_file *file_priv,
> +		  const struct drm_mode_fb_cmd2 *mode_cmd)
> +{
> +	const struct drm_format_info *info;
> +
> +	info = drm_get_format_info(dev, mode_cmd);
> +	if (!info)
> +		return ERR_PTR(-EINVAL);
> +
> +	if (mode_cmd->width * info->cpp[0] != mode_cmd->pitches[0]) {
> +		dev_dbg(dev->dev, "Invalid pitch: fb width must match pitch\n");
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	return drm_gem_fb_create(dev, file_priv, mode_cmd);
> +}
> +
>  static const struct drm_mode_config_funcs mxsfb_mode_config_funcs = {
> -	.fb_create		= drm_gem_fb_create,
> +	.fb_create		= mxsfb_fb_create,
>  	.atomic_check		= drm_atomic_helper_check,
>  	.atomic_commit		= drm_atomic_helper_commit,
>  };

-- 
Regards,

Laurent Pinchart