[PATCH] drm/i915/hdcp: Fix IS_METEORLAKE usage for HDCP line rekeying

[Matt Roper]

I'm not terribly familiar with HDCP, but from reading the spec my
understanding is that in general we need to enable rekeying for HDCP 1.4
and disable it for higher HDCP versions, right?  That would be the
expected "normal" programming for all platforms if we didn't have any
workarounds.  However the issue here is that we have a workaround
(Wa_16021352814) which affects the early steppings of certain platforms
and instructs us to "Prune timings with hblank below 138" instead of
disabling rekeying.

In that case, I'd expect the logic for this function to be something
like the following pseudocode:

    needs_wa_16021352814() {
        return IS_DISPLAY_STEP(IP_VER(14, 0), STEP_A0, STEP_D0) ||
               IS_DISPLAY_STEP(IP_VER(14, 1), STEP_A0, STEP_B0) ||
               IS_DISPLAY_STEP(IP_VER(20, 0), STEP_A0, STEP_B0);
    }

    intel_hdcp_disable_hdcp_line_rekeying() {
        assert(output is HDMI);
        assert(HDCP > 1.4);

        /*
         * Wa_16021352814: Rather than disabling rekeying, we need
         * to prune timings with hblank below 138 pixels, which is
         * taken care of in xxxxxx().
         */
        if (needs_wa_16021352814())
            return;

        if (DISPLAY_VER_FULL() >= IP_VER(14, 1))
                intel_de_rmw(TRANS_DDI_FUNC_CTL, ...);
        else
                intel_de_rmw(MTL_CHICKEN_TRANS, ...);
    }

And the logic to prune modes according to hblank for this workaround
would need to be programmed somewhere as well...has that already
happened?


Matt

On Mon, May 27, 2024 at 10:51:19AM +0530, Suraj Kandpal wrote:
> Replace IS_METEORLAKE usage with a more appropriate macro. While
> we are at it also add the stepping restrictions for other platforms.
> 
> Fixes: 6a3691ca4799 ("drm/i915/hdcp: Disable HDCP Line Rekeying for HDCP2.2 on HDMI")
> Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdcp.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index 02cbbbfd8e25..5767070248bb 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -42,10 +42,11 @@ intel_hdcp_disable_hdcp_line_rekeying(struct intel_encoder *encoder,
>  		return;
>  
>  	if (DISPLAY_VER(dev_priv) >= 14) {
> -		if (IS_METEORLAKE(dev_priv))
> +		if (IS_DISPLAY_IP_STEP(dev_priv, IP_VER(14, 0), STEP_D0, STEP_FOREVER))
>  			intel_de_rmw(dev_priv, MTL_CHICKEN_TRANS(hdcp->cpu_transcoder),
>  				     0, HDCP_LINE_REKEY_DISABLE);
> -		else
> +		else if (IS_DISPLAY_IP_STEP(dev_priv, IP_VER(14, 1), STEP_B0, STEP_FOREVER) ||
> +			 IS_DISPLAY_IP_STEP(dev_priv, IP_VER(20, 0), STEP_B0, STEP_FOREVER))
>  			intel_de_rmw(dev_priv, TRANS_DDI_FUNC_CTL(hdcp->cpu_transcoder),
>  				     0, TRANS_DDI_HDCP_LINE_REKEY_DISABLE);
>  	}
> -- 
> 2.43.2
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation