Re: [PATCH 2/8] drm/i915: Stop encryption for repeater with no sink

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

On Friday 02 February 2018 08:18 PM, Sean Paul wrote:
> On Fri, Feb 02, 2018 at 07:42:47PM +0530, Ramalingam C wrote:
>>
>> On Friday 02 February 2018 07:43 PM, Sean Paul wrote:
>>> On Fri, Feb 02, 2018 at 04:15:14PM +0530, Ramalingam C wrote:
>>>> If a HDCP repeater is detected with zero hdcp authenticated
>>>> downstream devices, there are two option as below:
>>>>
>>>> 1. Dont continue on second stage authentication. Disable encryption.
>>>> 2. Continue with second stage authentication excluding the KSV list and
>>>>      continue encryption on success.
>>>>
>>>> This patch adopts the option 1.
>>> It doesn't seem that hard to adopt option 2 and avoid failure. That would result
>>> in a better experience.
>> True. Not too much effort for option 2. But I am not seeing any ROI out of
>> it at this point.
>> what is the benefit of encrypting if repeater cant use it, as it has 0 sinks
>> attached to it.
>> Still do we want option two?
> Is it possible the repeater itself has video output? I'm also worried about
> non-compliant displays which may report having a repeater. If these aren't
> possible, I agree. Just beef up the comment like "If there are no downstream
> devices, spec requires we disable all encryption. So fail here to ensure hdcp is
> disabled"
>
> Sean

When spec provide an option that we can disable the HDCP encryption incase
of repeater with device count 0, that means repeaters cant have display.

Display which claims to be a repeater, mostly wont pass the second stage
authentication meant for repeaters. So we need not worry about them.

Sure as you mentioned i will rephrase the commit message with these informations.

--Ram

>
>> -Ram
>>>> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
>>>> ---
>>>>    drivers/gpu/drm/i915/intel_hdcp.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/intel_hdcp.c b/drivers/gpu/drm/i915/intel_hdcp.c
>>>> index 0021511ae4d7..182a3c8a4e4a 100644
>>>> --- a/drivers/gpu/drm/i915/intel_hdcp.c
>>>> +++ b/drivers/gpu/drm/i915/intel_hdcp.c
>>>> @@ -175,10 +175,10 @@ int intel_hdcp_auth_downstream(struct intel_connector *connector)
>>>>    		return -EPERM;
>>>>    	}
>>>> -	/* If there are no downstream devices, we're all done. */
>>>> +	/* If there are no downstream devices, we're not encrypting. */
>>>>    	num_downstream = DRM_HDCP_NUM_DOWNSTREAM(bstatus[0]);
>>>>    	if (num_downstream == 0)
>>>> -		return 0;
>>>> +		return -EINVAL;
>>>>    	ksv_fifo = kzalloc(num_downstream * DRM_HDCP_KSV_LEN, GFP_KERNEL);
>>>>    	if (!ksv_fifo)
>>>> -- 
>>>> 2.7.4
>>>>

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