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

[Neil Armstrong <narmstrong@baylibre.com>]

On 25/03/2019 12:37, Andrzej Hajda wrote:
> 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@kernel.org>
>> Fixes: 264fce6cc2c1 ("drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support")
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.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 :)

I made my best to make it barely readable...

We may need to reword this condition since on the DW-HMI in the Allwinner
H6, this is no more needed for scrambling !

> 
> Anyway:
> 
> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
> 
> 
> As I remember you can queue it to drm-misc, if not I can do it, just let
> me know.

I can and I'm queuing it right now, thanks for the review !

Neil

> 
> 
>  --
> 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) {
>>  			/*
> 
>