linux-kernel - Re: [PATCH] drm/bridge: dw-hdmi: disable SCDC configuration for invalid setups

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Date:   Mon, 25 Mar 2019 12:37:01 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Neil Armstrong <narmstrong@...libre.com>,
        Laurent.pinchart@...asonboard.com, heiko@...ech.de, robh@...nel.org
Cc:     linux-amlogic@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        jernej.skrabec@...l.net
Subject: Re: [PATCH] drm/bridge: dw-hdmi: disable SCDC configuration for
 invalid setups

On 15.03.2019 10:54, Neil Armstrong wrote:
> This patch is an attempt to limit HDMI 2.0 SCDC setup when :
> - the SoC embeds an HDMI 1.4 only controller
> - the EDID supports SCDC but not scrambling
> - the EDID supports SCDC scrambling but not for low TMDS bit rates,
>   while only supporting low TMDS bit rates
>
> This to avoid communicating with the SCDC DDC slave uncessary, and
> setting the DW-HDMI TMDS Scrambler setup when not supported by the
> underlying hardware.
>
> Reported-by: Rob Herring <robh@...nel.org>
> Fixes: 264fce6cc2c1 ("drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support")
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> ---
>
> Rob,
>
> this patch should also solve your issue with your 11' display, could you
> test it ?
> If this works, I will focus on the underlying issue where the RK3399 SoC
> freezes in your setup.
>
> Thanks,
> Neil
>
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 34 ++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index a63e5f0dae56..db761329a1e3 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -1037,6 +1037,31 @@ void dw_hdmi_phy_i2c_write(struct dw_hdmi *hdmi, unsigned short data,
>  }
>  EXPORT_SYMBOL_GPL(dw_hdmi_phy_i2c_write);
>  
> +/* Filter out invalid setups to avoid configuring SCDC and scrambling */
> +static bool dw_hdmi_support_scdc(struct dw_hdmi *hdmi)
> +{
> +	struct drm_display_info *display = &hdmi->connector.display_info;
> +
> +	/* Completely disable SCDC support for older controllers */
> +	if (hdmi->version < 0x200a)
> +		return false;
> +
> +	/* Disable if SCDC is not supported, or if an HF-VSDB block is absent */
> +	if (!display->hdmi.scdc.supported ||
> +	    !display->hdmi.scdc.scrambling.supported)
> +		return false;
> +
> +	/*
> +	 * Disable if display only support low TMDS rates and scrambling
> +	 * for low rates is not supported either
> +	 */
> +	if (!display->hdmi.scdc.scrambling.low_rates &&
> +	    display->max_tmds_clock <= 340000)
> +		return false;
> +
> +	return true;
> +}
> +
>  /*
>   * HDMI2.0 Specifies the following procedure for High TMDS Bit Rates:
>   * - The Source shall suspend transmission of the TMDS clock and data
> @@ -1055,7 +1080,7 @@ void dw_hdmi_set_high_tmds_clock_ratio(struct dw_hdmi *hdmi)
>  	unsigned long mtmdsclock = hdmi->hdmi_data.video_mode.mtmdsclock;
>  
>  	/* Control for TMDS Bit Period/TMDS Clock-Period Ratio */
> -	if (hdmi->connector.display_info.hdmi.scdc.supported) {
> +	if (dw_hdmi_support_scdc(hdmi)) {
>  		if (mtmdsclock > HDMI14_MAX_TMDSCLK)
>  			drm_scdc_set_high_tmds_clock_ratio(hdmi->ddc, 1);
>  		else
> @@ -1579,8 +1604,9 @@ static void hdmi_av_composer(struct dw_hdmi *hdmi,
>  
>  	/* Set up HDMI_FC_INVIDCONF */
>  	inv_val = (hdmi->hdmi_data.hdcp_enable ||
> -		   vmode->mtmdsclock > HDMI14_MAX_TMDSCLK ||
> -		   hdmi_info->scdc.scrambling.low_rates ?
> +		   (dw_hdmi_support_scdc(hdmi) &&
> +		    (vmode->mtmdsclock > HDMI14_MAX_TMDSCLK ||
> +		     hdmi_info->scdc.scrambling.low_rates)) ?
>  		HDMI_FC_INVIDCONF_HDCP_KEEPOUT_ACTIVE :
>  		HDMI_FC_INVIDCONF_HDCP_KEEPOUT_INACTIVE);


The condition is hard to read, but I have no idea atm how make it
compact and pretty :)

Anyway:

Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>


As I remember you can queue it to drm-misc, if not I can do it, just let
me know.


 --
Regards
Andrzej



>  
> @@ -1646,7 +1672,7 @@ static void hdmi_av_composer(struct dw_hdmi *hdmi,
>  	}
>  
>  	/* Scrambling Control */
> -	if (hdmi_info->scdc.supported) {
> +	if (dw_hdmi_support_scdc(hdmi)) {
>  		if (vmode->mtmdsclock > HDMI14_MAX_TMDSCLK ||
>  		    hdmi_info->scdc.scrambling.low_rates) {
>  			/*