Re: [PATCH 2/5] drm/i915: read Vprime thrice incase of mismatch

[Sean Paul <seanpaul@chromium.org>]

On Mon, Feb 26, 2018 at 10:42:36PM +0530, Ramalingam C wrote:
> In case of V prime mismatch, DP HDCP spec mandates the re-read of
> Vprime atleast twice.
> 
> DP HDCP CTS Test: 1B-05
> 
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_hdcp.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hdcp.c b/drivers/gpu/drm/i915/intel_hdcp.c
> index 730681d2dbfb..7ea55fa46f41 100644
> --- a/drivers/gpu/drm/i915/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/intel_hdcp.c
> @@ -150,7 +150,7 @@ int intel_hdcp_auth_downstream(struct intel_digital_port *intel_dig_port,
>  	struct drm_i915_private *dev_priv;
>  	u32 vprime, sha_text, sha_leftovers, rep_ctl;
>  	u8 bstatus[2], num_downstream, *ksv_fifo;
> -	int ret, i, j, sha_idx;
> +	int ret, i, j, sha_idx, tries = 3;
>  
>  	dev_priv = intel_dig_port->base.base.dev->dev_private;
>  
> @@ -189,6 +189,7 @@ int intel_hdcp_auth_downstream(struct intel_digital_port *intel_dig_port,
>  	if (ret)
>  		return ret;
>  
> +read_v_prime:

Instead of using the label for retry, please break it out into a function that's
enclosed in a retry loop.

Sean

>  	/* Process V' values from the receiver */
>  	for (i = 0; i < DRM_HDCP_V_PRIME_NUM_PARTS; i++) {
>  		ret = shim->read_v_prime_part(intel_dig_port, i, &vprime);
> @@ -385,6 +386,13 @@ int intel_hdcp_auth_downstream(struct intel_digital_port *intel_dig_port,
>  		return -ETIMEDOUT;
>  	}
>  	if (!(I915_READ(HDCP_REP_CTL) & HDCP_SHA1_V_MATCH)) {
> +
> +		/*
> +		 * When V prime mismatches, DP Spec mandates re-read of
> +		 * V prime atleast twice.
> +		 */
> +		if (--tries)
> +			goto read_v_prime;
>  		DRM_ERROR("SHA-1 mismatch, HDCP failed\n");
>  		return -ENXIO;
>  	}
> -- 
> 2.7.4
> 

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