Re: [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4

Rodrigo Vivi
2018-03-12T19:39:19Z

On Fri, Mar 09, 2018 at 11:49:44PM +0000, Atwood, Matthew S wrote:
> On Thu, 2018-03-08 at 09:22 +0200, Jani Nikula wrote:
> > On Wed, 07 Mar 2018, matthew.s.atwood@intel.com wrote:
> > >
> > > From: Matt Atwood <matthew.s.atwood@intel.com>
> > >
> > > DP_TRAINING_AUX_RD_INTERVAL with DP 1.3 spec changed bit scheeme
> > > from 8
> > > bits to 7 in DPCD 0x000e. The 8th bit is used to identify extended
> > > receiver capabilities. For panels that use this new feature wait
> > > interval
> > > would be increased by 512 ms, when spec is max 16 ms. This behavior
> > > is
> > > described in table 2-158 of DP 1.4 spec address 0000eh.
> > >
> > > With the introduction of DP 1.4 spec main link clock recovery was
> > > standardized to 100 us regardless of TRAINING_AUX_RD_INTERVAL
> > > value.
> > >
> > > To avoid breaking panels that are not spec compiant we now warn on
> > > invalid values.
> > >
> > > V2: commit title/message, masking all 7 bits, warn on out of spec
> > > values.
> > > V3: commit message, make link train clock recovery follow DP 1.4
> > > spec.
> > > V4: style changes
> > > V5: typo
> > >
> > > Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_dp_helper.c | 18 ++++++++++++++----
> > >  include/drm/drm_dp_helper.h     |  6 ++++++
> > >  2 files changed, 20 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > > b/drivers/gpu/drm/drm_dp_helper.c
> > > index adf79be..cdb04c9 100644
> > > --- a/drivers/gpu/drm/drm_dp_helper.c
> > > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > > @@ -119,18 +119,28 @@ u8
> > > drm_dp_get_adjust_request_pre_emphasis(const u8
> > > link_status[DP_LINK_STATUS_SI
> > >  EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
> > >
> > >  void drm_dp_link_train_clock_recovery_delay(const u8
> > > dpcd[DP_RECEIVER_CAP_SIZE]) {
> > > - if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> > > + int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > > DP_TRAINING_AUX_RD_MASK;
> > > +
> > > + if (rd_interval > 4)
> > > + DRM_DEBUG_KMS("AUX interval %d, out of range (max
> > > 4)", rd_interval);
> > \n missing.
> will do
> >
> > >
> > > +
> > > + if (rd_interval == 0 || (dpcd[DP_DPCD_REV] >= DP_REV_14))
> > >   udelay(100);
> > >   else
> > > - mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> > > + mdelay(rd_interval * 4);
> > >  }
> > >  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
> > >
> > >  void drm_dp_link_train_channel_eq_delay(const u8
> > > dpcd[DP_RECEIVER_CAP_SIZE]) {
> > > - if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> > > + int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > > DP_TRAINING_AUX_RD_MASK;
> > > +
> > > + if (rd_interval > 4)
> > > + DRM_DEBUG_KMS("AUX interval %d, out of range (max
> > > 4)", rd_interval);
> > \n missing.
> will do
> >
> > >
> > > +
> > > + if (rd_interval == 0)
> > >   udelay(400);
> > >   else
> > > - mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> > > + mdelay(rd_interval * 4);
> > >  }
> > >  EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
> > >
> > > diff --git a/include/drm/drm_dp_helper.h
> > > b/include/drm/drm_dp_helper.h
> > > index da58a42..1269ef8 100644
> > > --- a/include/drm/drm_dp_helper.h
> > > +++ b/include/drm/drm_dp_helper.h
> > > @@ -64,6 +64,11 @@
> > >  /* AUX CH addresses */
> > >  /* DPCD */
> > >  #define DP_DPCD_REV                         0x000
> > > +# define DP_REV_10                          0x10
> > > +# define DP_REV_11                          0x11
> > > +# define DP_REV_12                          0x12
> > > +# define DP_REV_13                          0x13
> > > +# define DP_REV_14                          0x14
> > I am not sure what good these buy us, but if people think they're the
> > way to go, then so be it. Just bear in mind that per spec, "The DPCD
> > revision number does not necessarily match the DisplayPort version
> > number." so "DP_REV" doesn't actually mean *DP* revision.
> >
> >
> > BR,
> > Jani.
> you're right likely a better name is DPCD_REV_XX. I think we sill want
> to base the main-link clock recovery on time on this value. Next
> revision will include this naming convention.

yep, I believe we need this anyways even without a necessarily match.
And DPCD_REV_ seems better indeed.

> >
> > >
> > >
> > >  #define DP_MAX_LINK_RATE                    0x001
> > >
> > > @@ -118,6 +123,7 @@
> > >  # define DP_DPCD_DISPLAY_CONTROL_CAPABLE     (1 << 3) /* edp v1.2
> > > or higher */
> > >
> > >  #define DP_TRAINING_AUX_RD_INTERVAL         0x00e   /* XXX 1.2? */
> > > +# define DP_TRAINING_AUX_RD_MASK            0x7F    /* 1.3 */
> Rodrigo has shown me a DP 1.2 spec that had this change and conflicts
> with my copy so I'll be changing to XXX 1.2

I thought you had convinced me otherwise that day. The other bit
on this range didn't exist on this so the mask wouldn't be needed,
but the max value there is anyways == 4 so it can apply anyways.

but up to you how you want to proceed here.

>
> Matt
> > >
> > >  #define DP_ADAPTER_CAP     0x00f   /* 1.2
> > > */
> > >  # define DP_FORCE_LOAD_SENSE_CAP     (1 << 0)
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