[PATCHv2] drm/sun4i: validate modes for HDMI

[Maxime Ripard]

Hi Hans,

On Fri, Dec 08, 2017 at 04:48:47PM +0100, Hans Verkuil wrote:
> When I connected my cubieboard running 4.15-rc1 to my 4k display I got no picture. Some
> digging found that there is no check against the upper pixelclock limit of the HDMI
> output, so X selects a 4kp60 format at 594 MHz, which obviously won't work.
> 
> The patch below adds a check for the upper bound of what this hardware can do, and
> it checks if the requested tmds clock can be obtained.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
> ---
>  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> index dda904ec0534..c10400a19b33 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> @@ -208,8 +208,27 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector)
>  	return ret;
>  }
> 
> +static int sun4i_hdmi_mode_valid(struct drm_connector *connector,
> +				 struct drm_display_mode *mode)
> +{
> +	struct sun4i_hdmi *hdmi = drm_connector_to_sun4i_hdmi(connector);
> +	unsigned long rate = mode->clock * 1000;
> +	long rounded_rate;
> +
> +	/* 165 MHz is the typical max pixelclock frequency for HDMI <= 1.2 */
> +	if (rate > 165000000)
> +		return MODE_CLOCK_HIGH;
> +	rounded_rate = clk_round_rate(hdmi->tmds_clk, rate);
> +	if (rounded_rate < rate)
> +		return MODE_CLOCK_LOW;
> +	if (rounded_rate > rate)
> +		return MODE_CLOCK_HIGH;
> +	return MODE_OK;
> +}

This looks much better, thanks!

One thing that I was mentionning in my other mail is that our rate
rounding might not provide the exact TMDS clock rate advertised by the
EDID, while staying in the tolerancy.

We've raised this issue before, without coming to a conclusion. Would
you happen to know what that tolerancy would be on an HDMI link?

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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