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SubjectRe: [PATCH] drm/bridge: dw-hdmi: disable SCDC configuration for invalid setups
On Fri, Mar 15, 2019 at 4:54 AM Neil Armstrong <narmstrong@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@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 ?

That works for me.

Tested-by: Rob Herring <robh@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
>

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