[PATCHv4] drm/sun4i: validate modes for HDMI

[Daniel Vetter]

On Fri, Dec 15, 2017 at 05:46:19PM +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.
> 
> It also allows for the ± 0.5% pixel clock variation that the HDMI spec permits.
> 
> That code is based on commit 22d0be2a557e53a22feb484e8fce255fe09e6ad5 from
> Jose Abreu for drm/arc.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
> ---
> Changes since v3:
> - Move the mode_valid callback to struct drm_encoder_helper_funcs.
>   I'm assuming this is the correct struct, since this check is specific to the
>   hdmi encoder.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

I think sun4i is in drm-misc, so feel free to push.

Cheers, Daniel


> Changes since v2:
> - Allow for the 0.5% variation.
> ---
>  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> index dda904ec0534..500b6fb3e028 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> @@ -175,11 +175,31 @@ static void sun4i_hdmi_mode_set(struct drm_encoder *encoder,
>  	writel(val, hdmi->base + SUN4I_HDMI_VID_TIMING_POL_REG);
>  }
> 
> +static enum drm_mode_status sun4i_hdmi_mode_valid(struct drm_encoder *encoder,
> +					const struct drm_display_mode *mode)
> +{
> +	struct sun4i_hdmi *hdmi = drm_encoder_to_sun4i_hdmi(encoder);
> +	unsigned long rate = mode->clock * 1000;
> +	unsigned long diff = rate / 200; /* +-0.5% allowed by HDMI spec */
> +	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 > 0 &&
> +	    max_t(unsigned long, rounded_rate, rate) -
> +	    min_t(unsigned long, rounded_rate, rate) < diff)
> +		return MODE_OK;
> +	return MODE_NOCLOCK;
> +}
> +
>  static const struct drm_encoder_helper_funcs sun4i_hdmi_helper_funcs = {
>  	.atomic_check	= sun4i_hdmi_atomic_check,
>  	.disable	= sun4i_hdmi_disable,
>  	.enable		= sun4i_hdmi_enable,
>  	.mode_set	= sun4i_hdmi_mode_set,
> +	.mode_valid	= sun4i_hdmi_mode_valid,
>  };
> 
>  static const struct drm_encoder_funcs sun4i_hdmi_funcs = {
> -- 
> 2.15.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch