On Fri, Feb 02, 2018 at 08:33:38PM +0530, Ramalingam C wrote:
> 
> 
> 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.

Not just the commit message. Please also update the comment in the code so it's
clear.

Sean

> 
> --Ram
> 
> > 
> > > -Ram
> > > > > Signed-off-by: Ramalingam C <ramalinga...@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
> > > > > 
> 

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