Re: [PATCH 4/8] drm/i915: Retry HDCP BKSV read

Sean Paul
2018-02-02T14:16:22Z

On Fri, Feb 02, 2018 at 04:15:16PM +0530, Ramalingam C wrote:
> When BKSV is invalid, to mitigate any communication errors,
> BKSV is read once again.

Why is the Bksv read any more volatile than other reads? If the channel is
noisy, the retries should be done in the shim implementation (I think there are
already i2c retries).

Sean

>
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> ---
> drivers/gpu/drm/i915/intel_hdcp.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_hdcp.c b/drivers/gpu/drm/i915/intel_hdcp.c
> index b3f407cef8b0..fa2e7c727d00 100644
> --- a/drivers/gpu/drm/i915/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/intel_hdcp.c
> @@ -401,7 +401,7 @@ static int intel_hdcp_auth(struct intel_connector *connector)
> struct drm_i915_private *dev_priv;
> enum port port;
> unsigned long r0_prime_gen_start;
> - int ret, i;
> + int ret, i, retry = 1;
> union {
> u32 reg[2];
> u8 shim[DRM_HDCP_AN_LEN];
> @@ -443,11 +443,16 @@ static int intel_hdcp_auth(struct intel_connector *connector)
> r0_prime_gen_start = jiffies;
>
> memset(&bksv, 0, sizeof(bksv));
> - ret = shim->read_bksv(intel_dig_port, bksv.shim);
> +
> + do {
> + ret = shim->read_bksv(intel_dig_port, bksv.shim);
> + if (!ret)
> + if (!intel_hdcp_is_ksv_valid(bksv.shim))
> + ret = -ENODEV;
> + } while (ret && retry--);
> +
> if (ret)
> return ret;
> - else if (!intel_hdcp_is_ksv_valid(bksv.shim))
> - return -ENODEV;
>
> I915_WRITE(PORT_HDCP_BKSVLO(port), bksv.reg[0]);
> I915_WRITE(PORT_HDCP_BKSVHI(port), bksv.reg[1]);
> --
> 2.7.4
>

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