[PATCH v6 08/10] drm/i915: Check pixel rate for DP to VGA dongle

[Daniel Vetter]

On Wed, Jul 06, 2016 at 02:04:52PM +0300, Mika Kahola wrote:
> Filter out a mode that exceeds the max pixel rate setting
> for DP to VGA dongle. This is defined in DPCD register 0x81
> if detailed cap info i.e. info field is 4 bytes long and
> it is available for DP downstream port.
> 
> The register defines the pixel rate divided by 8 in MP/s.
> 
> v2: DPCD read outs and computation moved to drm (Ville, Daniel)
> v3: Sink pixel rate computation moved to drm_dp_max_sink_dotclock()
>     function (Daniel)
> v4: Use of drm_dp_helper.c routines to compute max pixel clock (Ville)
> v5: Use of intel_dp->downstream_ports to read out port capabilities.
>     Code restructuring (Ville)
> 
> Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index ffa43ec..76a654e 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -190,6 +190,20 @@ intel_dp_max_data_rate(int max_link_clock, int max_lanes)
>  	return (max_link_clock * max_lanes * 8) / 10;
>  }
>  
> +static int
> +intel_dp_downstream_max_clock(struct intel_dp *intel_dp, int clock)
> +{
> +	int dp_ds_clk;
> +
> +	dp_ds_clk = drm_dp_downstream_max_clock(intel_dp->dpcd,
> +						intel_dp->downstream_ports);
> +
> +	if (dp_ds_clk == 0)
> +		return clock;
> +
> +	return min(clock, dp_ds_clk);
> +}
> +
>  static enum drm_mode_status
>  intel_dp_mode_valid(struct drm_connector *connector,
>  		    struct drm_display_mode *mode)
> @@ -201,6 +215,18 @@ intel_dp_mode_valid(struct drm_connector *connector,
>  	int max_rate, mode_rate, max_lanes, max_link_clock;
>  	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
>  
> +	bool is_branch_device = intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> +		DP_DWN_STRM_PORT_PRESENT;
> +	int type;
> +
> +	if (is_branch_device) {

Shouldn't we move this check into the drm dp helper? It can always return
0 for "no downstream port restrictions".

> +		type = intel_dp->downstream_ports[0] & DP_DS_PORT_TYPE_MASK;
> +
> +		if (type == DP_DS_PORT_TYPE_VGA)

Same here.
-Daniel

> +			max_dotclk = intel_dp_downstream_max_clock(intel_dp,
> +								   max_dotclk);
> +	}
> +
>  	if (is_edp(intel_dp) && fixed_mode) {
>  		if (mode->hdisplay > fixed_mode->hdisplay)
>  			return MODE_PANEL;
> -- 
> 1.9.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch