linux-kernel - Re: [PATCH v2 6/8] drm/imx: support handling bridge timings bus flags

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Date:   Fri, 14 Sep 2018 13:00:29 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     linus.walleij@...aro.org, airlied@...ux.ie, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, s.hauer@...gutronix.de,
        p.zabel@...gutronix.de, kernel@...gutronix.de,
        fabio.estevam@....com, linux-imx@....com, architt@...eaurora.org,
        a.hajda@...sung.com, gustavo@...ovan.org,
        maarten.lankhorst@...ux.intel.com, sean@...rly.run,
        marcel.ziswiler@...adex.com, max.krummenacher@...adex.com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/8] drm/imx: support handling bridge timings bus flags

Hi Stefan,

Thank you for the patch.

On Wednesday, 12 September 2018 21:32:20 EEST Stefan Agner wrote:
> A bridge might require specific settings for the pixel data on
> the bus. Copy the bus flags from the bridge timings if a bridge
> is in use.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
>  drivers/gpu/drm/imx/parallel-display.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/imx/parallel-display.c
> b/drivers/gpu/drm/imx/parallel-display.c index aefd04e18f93..7798a0621df7
> 100644
> --- a/drivers/gpu/drm/imx/parallel-display.c
> +++ b/drivers/gpu/drm/imx/parallel-display.c
> @@ -239,6 +239,9 @@ static int imx_pd_bind(struct device *dev, struct device
> *master, void *data) if (ret && ret != -ENODEV)
>  		return ret;
> 
> +	if (imxpd->bridge && imxpd->bridge->timings)
> +		imxpd->bus_flags = imxpd->bridge->timings->input_bus_flags;

As explained in different replies in this mail thread (and in v1), we need 
something more complex than this.

How about creating a helper function that would take a sampling edge, setup 
and hold times, clock frequency and internal delay on the driving side, and 
return which edge to drive the data on ? I agree with you that the logic is 
complex, so we shouldn't duplicate it in multiple drivers. If you submit such 
a patch I'll implement support for configuring the clock edge in the R-Car DU 
driver and test it with the ADV7123.

>  	imxpd->dev = dev;
> 
>  	ret = imx_pd_register(drm, imxpd);

-- 
Regards,

Laurent Pinchart