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

[Ramalingam C <ramalingam.c@intel.com>]

On Friday 02 February 2018 07:46 PM, Sean Paul wrote:
> 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
True. But compliance spec says that when we determine that bksv is 
invalid (not with 20 1s), we should re-read and confirm.
CTS test 1A-05 test expect this behavior.

--Ram

>
>> 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
>>

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