Re: [PATCH] drm/i915/hdcp: Disable HDCP Line Rekeying for HDCP2.2 on HDMI

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 16 Apr 2024, Suraj Kandpal <suraj.kandpal@intel.com> wrote:
> Disable HDCP Line Rekeying when HDCP ver > 1.4 and when we are
> on HDMI TMDS operation for DISPLAY_VEY >= 14.
> WA: 16022217614
> Bspec: 49273
> Bspec: 69964
>
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdcp.c | 16 ++++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h           |  1 +
>  2 files changed, 17 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index d5ed4c7dfbc0..15af6e184ef8 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -30,6 +30,20 @@
>  #define KEY_LOAD_TRIES	5
>  #define HDCP2_LC_RETRY_CNT			3
>  
> +static void
> +intel_hdcp_disable_hdcp_line_rekeying(struct intel_encoder *encoder,
> +				      struct intel_hdcp *hdcp)
> +{
> +	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> +
> +	if (encoder->type != INTEL_OUTPUT_HDMI)
> +		return;

Reading code, I came across this line, originating from commit
6a3691ca4799 ("drm/i915/hdcp: Disable HDCP Line Rekeying for HDCP2.2 on
HDMI") i.e. this patch here. The function has been expanded since, but
this remains at the top of the function.

encoder->type == INTEL_OUTPUT_HDMI is only true for pre-DDI platforms,
but they don't have HDCP.

The entire function is a big NOP, and always has been.


BR,
Jani.


> +
> +	if (DISPLAY_VER(dev_priv) >= 14)
> +		intel_de_rmw(dev_priv, TRANS_DDI_FUNC_CTL(hdcp->cpu_transcoder),
> +			     TRANS_DDI_HDCP_LINE_REKEY_DISABLE, 1);
> +}
> +
>  static int intel_conn_to_vcpi(struct intel_atomic_state *state,
>  			      struct intel_connector *connector)
>  {
> @@ -2005,6 +2019,8 @@ static int _intel_hdcp2_enable(struct intel_atomic_state *state,
>  		    connector->base.base.id, connector->base.name,
>  		    hdcp->content_type);
>  
> +	intel_hdcp_disable_hdcp_line_rekeying(connector->encoder, hdcp);
> +
>  	ret = hdcp2_authenticate_and_encrypt(state, connector);
>  	if (ret) {
>  		drm_dbg_kms(&i915->drm, "HDCP2 Type%d  Enabling Failed. (%d)\n",
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 3f34efcd7d6c..fbf4623cd536 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -5630,6 +5630,7 @@ enum skl_power_gate {
>  #define  TRANS_DDI_EDP_INPUT_B_ONOFF	(5 << 12)
>  #define  TRANS_DDI_EDP_INPUT_C_ONOFF	(6 << 12)
>  #define  TRANS_DDI_EDP_INPUT_D_ONOFF	(7 << 12)
> +#define  TRANS_DDI_HDCP_LINE_REKEY_DISABLE	REG_BIT(12)
>  #define  TRANS_DDI_MST_TRANSPORT_SELECT_MASK	REG_GENMASK(11, 10)
>  #define  TRANS_DDI_MST_TRANSPORT_SELECT(trans)	\
>  	REG_FIELD_PREP(TRANS_DDI_MST_TRANSPORT_SELECT_MASK, trans)

-- 
Jani Nikula, Intel