[Intel-gfx] [PATCH 1/5] drm/i915: Read HDCP R0 thrice in case of mismatch

[Sean Paul]

On Mon, Feb 26, 2018 at 10:42:35PM +0530, Ramalingam C wrote:
> As per DP spec when R0 mismatch is detected, HDCP source supported
> re-read the R0 atleast twice.
> 
> And For HDMI and DP minimum wait required for the R0 availability is
> 100mSec. So this patch changes the wait time to 100mSec but retries
> twice with the time interval of 100mSec for each attempt.

"R0' must be available for the HDCP Transmitter to read within 100
milliseconds from the time that the HDCP Transmitter finishes writing Aksv to
the video receiver."

100ms is a minimum, waiting for 300ms is quite generous.

The retry is to account for link errors, so there's no need to include the wait
in the retry loop.

Sean

> 
> DP CTS Test: 1A-06.
> 
> Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_hdcp.c | 34 ++++++++++++++++++++++------------
>  1 file changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hdcp.c b/drivers/gpu/drm/i915/intel_hdcp.c
> index 14ca5d3057a7..730681d2dbfb 100644
> --- a/drivers/gpu/drm/i915/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/intel_hdcp.c
> @@ -496,25 +496,35 @@ static int intel_hdcp_auth(struct intel_digital_port *intel_dig_port,
>  	}
>  
>  	/*
> -	 * Wait for R0' to become available. The spec says 100ms from Aksv, but
> -	 * some monitors can take longer than this. We'll set the timeout at
> -	 * 300ms just to be sure.
> +	 * Wait for R0' to become available. The spec says minimum 100ms from
> +	 * Aksv, but some monitors can take longer than this. So we are
> +	 * combinely waiting for 300mSec just to be sure in case of HDMI.
> +	 * DP HDCP Spec mandates the two more reattempt to read R0, incase
> +	 * of R0 mismatch.
>  	 *
>  	 * On DP, there's an R0_READY bit available but no such bit
>  	 * exists on HDMI. Since the upper-bound is the same, we'll just do
>  	 * the stupid thing instead of polling on one and not the other.
>  	 */
> -	wait_remaining_ms_from_jiffies(r0_prime_gen_start, 300);
>  
> -	ri.reg = 0;
> -	ret = shim->read_ri_prime(intel_dig_port, ri.shim);
> -	if (ret)
> -		return ret;
> -	I915_WRITE(PORT_HDCP_RPRIME(port), ri.reg);
> +	tries = 3;
> +	for (i = 0; i < tries; i++) {
> +		wait_remaining_ms_from_jiffies(r0_prime_gen_start,
> +					       100 * (i + 1));
>  
> -	/* Wait for Ri prime match */
> -	if (wait_for(I915_READ(PORT_HDCP_STATUS(port)) &
> -		     (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1)) {
> +		ri.reg = 0;
> +		ret = shim->read_ri_prime(intel_dig_port, ri.shim);
> +		if (ret)
> +			return ret;
> +		I915_WRITE(PORT_HDCP_RPRIME(port), ri.reg);
> +
> +		/* Wait for Ri prime match */
> +		if (!wait_for(I915_READ(PORT_HDCP_STATUS(port)) &
> +		    (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1))
> +			break;
> +	}
> +
> +	if (i == tries) {
>  		DRM_ERROR("Timed out waiting for Ri prime match (%x)\n",
>  			  I915_READ(PORT_HDCP_STATUS(port)));
>  		return -ETIMEDOUT;
> -- 
> 2.7.4
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS