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

[Rob Herring]

On Fri, Mar 15, 2019 at 4:54 AM Neil Armstrong <narmstrong at baylibre.com> 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 at kernel.org>
> Fixes: 264fce6cc2c1 ("drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support")
> Signed-off-by: Neil Armstrong <narmstrong at baylibre.com>
> ---
>
> Rob,
>
> this patch should also solve your issue with your 11' display, could you
> test it ?

That works for me.

Tested-by: Rob Herring <robh at kernel.org>

Too answer your question on the other thread, there's not really any
model name for the panel I have. Probably what's in the EDID is the
best thing to go on.

Here's the panel on Amazon:

https://www.amazon.com/gp/product/B07GDDG3WJ/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1

> 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);
>
> @@ -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) {
>                         /*
> --
> 2.20.1
>