On Wed, Nov 28, 2018 at 11:09:46AM +0200, Jani Nikula wrote:
> On Tue, 27 Nov 2018, Manasi Navare <manasi.d.navare@xxxxxxxxx> wrote:
> > From: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
> >
> > According to DP spec (2.9.3.1 of DP 1.4) if
> > EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT is set the addresses in DPCD
> > 02200h through 0220Fh shall contain the DPRX's true capability. These
> > values will match 00000h through 0000Fh, except for DPCD_REV,
> > MAX_LINK_RATE, DOWN_STREAM_PORT_PRESENT.
> >
> > Read from DPCD once for all 3 values as this is an expensive operation.
> > Spec mentions that all of address space 02200h through 0220Fh should
> > contain the right information however currently only 3 values can
> > differ.
> >
> > There is no address space in the intel_dp->dpcd struct for addresses
> > 02200h through 0220Fh, and since so much of the data is a identical,
> > simply overwrite the values stored in 00000h through 0000Fh with the
> > values that can be overwritten from addresses 02200h through 0220Fh.
> >
> > This patch helps with backward compatibility for devices pre DP1.3.
> >
> > v2: read only dpcd values which can be affected, remove incorrect check,
> > split into drm include changes into separate patch, commit message,
> > verbose debugging statements during overwrite.
> > v3: white space fixes
> > v4: make path dependent on DPCD revision > 1.2
> > v5: split into function, removed DPCD rev check
> > v6: add debugging prints for early exit conditions
> > v7 (From Manasi):
> > * Memcpy, memcmp and debig logging based on sizeof(dpcd_ext) (Jani N)
> > * Exit early (Jani N)
> >
> > Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> > Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> > Signed-off-by: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
> > Tested-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> > Acked-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/intel_dp.c | 41 +++++++++++++++++++++++++++++++++
> > 1 file changed, 41 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 70ae3d57316b..a9eb14a4ab27 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3802,6 +3802,45 @@ intel_dp_link_down(struct intel_encoder *encoder,
> > }
> > }
> >
> > +static void
> > +intel_dp_extended_receiver_capabilities(struct intel_dp *intel_dp)
> > +{
> > + u8 dpcd_ext[6];
> > +
> > + /*
> > + * Prior to DP1.3 the bit represented by
> > + * DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT was reserved.
> > + * if it is set DP_DPCD_REV at 0000h could be at a value less than
> > + * the true capability of the panel. The only way to check is to
> > + * then compare 0000h and 2200h.
> > + */
> > + if (!(intel_dp->dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > + DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
> > + return;
> > +
> > + DRM_DEBUG_KMS("DPCD: Reading extended receiver capabilities\n");
>
> Superfluous debug logging.
Will get rid of this
>
> > +
> > + if (drm_dp_dpcd_read(&intel_dp->aux, DP_DP13_DPCD_REV,
> > + &dpcd_ext, sizeof(dpcd_ext)) != sizeof(dpcd_ext)) {
> > + DRM_ERROR("DPCD failed read at extended capabilities\n");
>
> Most of our dpcd failures are logged using DRM_DEBUG_KMS. The ones that
> log DRM_ERROR seem to be very recent additions deviating from the debug
> loggin practice. There isn't much the user can do, really.
Here this change from DEBUG_KMS to DRM_ERROR was as per Rodrigo's comment
on the initial patch. (https://patchwork.freedesktop.org/patch/240452/)
Also IMO it should be an error since it will give unexpected results as we were
unable to get the true extended capabilities.
>
> > + return;
> > + }
> > + if (intel_dp->dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> > + DRM_DEBUG_KMS("DPCD extended DPCD rev less than base DPCD rev\n");
>
> Okay, seems like a rare event.
Again this check and logging comes from Rodrigo's review comments on the initial patch.
https://patchwork.freedesktop.org/patch/240452/
>
> > + return;
> > + }
> > + if (!memcmp(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext))) {
> > + DRM_DEBUG_KMS("Extended Receiver Cap DPCD match the base DPCD\n");
>
> I don't think this debug logging is needed.
Sure will get rid of this.
>
> > + return;
> > + }
> > +
> > + DRM_DEBUG_KMS("Base DPCD: %*ph\n", (int)sizeof(dpcd_ext), intel_dp->dpcd);
>
> Using sizeof(dpcd_ext) when printing something else is a red flag. You
> could log the whole dpcd here.
>
> DRM_DEBUG_KMS("DPCD: %*ph (base)\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
Yes will do this.
>
> > + DRM_DEBUG_KMS("Extended Receiver Cap DPCD: %*ph\n",
> > + (int)sizeof(dpcd_ext), dpcd_ext);
>
> The caller will log the *updated* DPCD right after this returns, you
> don't need to log dpcd_ext.
Okay agreed, I will get rid of this debug print since the caller already prints it.
>
> > + memcpy(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext));
> > +}
> > +
> > +
>
> Superfluous newline.
Will remove.
>
> > bool
> > intel_dp_read_dpcd(struct intel_dp *intel_dp)
> > {
> > @@ -3809,6 +3848,8 @@ intel_dp_read_dpcd(struct intel_dp *intel_dp)
> > sizeof(intel_dp->dpcd)) < 0)
> > return false; /* aux transfer failed */
> >
> > + intel_dp_extended_receiver_capabilities(intel_dp);
> > +
> > DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
>
> One other alternative is to have
> intel_dp_extended_receiver_capabilities() return true if the cap exists
> and is different from current DPCD, and *all* DPCD logging would be done
> here. Both the old and the new. Like so:
>
> DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
> if (intel_dp_extended_receiver_capabilities(intel_dp))
> DRM_DEBUG_KMS("DPCD: %*ph\n (ext)", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
>
I like the firts idea better where we print the old DPCD before memcpy and caller prints the DPCD (new/old)
anyways after return so will stick to that.
Manasi
> BR,
> Jani.
>
> >
> > return intel_dp->dpcd[DP_DPCD_REV] != 0;
>
> --
> Jani Nikula, Intel Open Source Graphics Center
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