[PATCH] drm/sun4i: validate modes for HDMI

[Hans Verkuil]

Please ignore, this patch was on top of my old hack instead of being a proper patch.
I'll resend.

	Hans

On 12/08/2017 04:45 PM, 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>
> ---
> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> index 6d19d2ac68d1..62d52102d0f7 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> @@ -211,7 +211,17 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector)
>  static int sun4i_hdmi_mode_valid(struct drm_connector *connector,
>  				 struct drm_display_mode *mode)
>  {
> -	if (mode->clock > 170000)
> +	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;
>  }
>