[Intel-gfx] [PATCHv2] drm/i915/display/dp: On AUX xfer timeout restart freshly
Murthy, Arun R
arun.r.murthy at intel.com
Mon Jun 12 14:15:59 UTC 2023
> -----Original Message-----
> From: Deak, Imre <imre.deak at intel.com>
> Sent: Monday, June 12, 2023 6:28 PM
> To: Murthy, Arun R <arun.r.murthy at intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCHv2] drm/i915/display/dp: On AUX xfer timeout
> restart freshly
>
> On Mon, Jun 12, 2023 at 02:47:37PM +0300, Murthy, Arun R wrote:
> > > -----Original Message-----
> > > From: Deak, Imre <imre.deak at intel.com>
> > > Sent: Monday, June 12, 2023 5:07 PM
> > > To: Murthy, Arun R <arun.r.murthy at intel.com>
> > > Cc: intel-gfx at lists.freedesktop.org
> > > Subject: Re: [Intel-gfx] [PATCHv2] drm/i915/display/dp: On AUX xfer
> > > timeout restart freshly
> > >
> > > On Thu, Jun 08, 2023 at 03:02:18PM +0530, Arun R Murthy wrote:
> > > > At the begining of the aux transfer a check for aux control busy
> > > > bit is done. Then as per the spec on aux transfer timeout, need to
> > > > retry freshly for 3 times with a delay which is taken care by the
> > > > control register.
> > > > On each of these 3 trials a check for busy has to be done so as to
> > > > start freshly.
> > > >
> > > > v2: updated the commit message
> > > >
> > > > Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> > > > ---
> > > > drivers/gpu/drm/i915/display/intel_dp_aux.c | 50
> > > > +++++++++------------
> > > > 1 file changed, 22 insertions(+), 28 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > > > b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > > > index 197c6e81db14..25090542dd9f 100644
> > > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > > > @@ -273,30 +273,6 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
> > > > * it using the same AUX CH simultaneously
> > > > */
> > > >
> > > > - /* Try to wait for any previous AUX channel activity */
> > > > - for (try = 0; try < 3; try++) {
> > > > - status = intel_de_read_notrace(i915, ch_ctl);
> > > > - if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
> > > > - break;
> > > > - msleep(1);
> > > > - }
> > > > - /* just trace the final value */
> > > > - trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> > > > -
> > > > - if (try == 3) {
> > > > - const u32 status = intel_de_read(i915, ch_ctl);
> > > > -
> > > > - if (status != intel_dp->aux_busy_last_status) {
> > > > - drm_WARN(&i915->drm, 1,
> > > > - "%s: not started (status 0x%08x)\n",
> > > > - intel_dp->aux.name, status);
> > > > - intel_dp->aux_busy_last_status = status;
> > > > - }
> > > > -
> > > > - ret = -EBUSY;
> > > > - goto out;
> > > > - }
> > > > -
> > > > /* Only 5 data registers! */
> > > > if (drm_WARN_ON(&i915->drm, send_bytes > 20 || recv_size > 20)) {
> > > > ret = -E2BIG;
> > > > @@ -304,14 +280,31 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
> > > > }
> > > >
> > > > while ((aux_clock_divider = intel_dp-
> > > >get_aux_clock_divider(intel_dp, clock++))) {
> > > > - u32 send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
> > > > + /* Must try at least 3 times according to DP spec */
> > > > + for (try = 0; try < 5; try++) {
> > > > + u32 send_ctl =
> > > > + intel_dp->get_aux_send_ctl(intel_dp,
> > > > send_bytes,
> > > >
> > > > aux_clock_divider);
> > > >
> > > > - send_ctl |= aux_send_ctl_flags;
> > > > + send_ctl |= aux_send_ctl_flags;
> > >
> > > Why is send_ctl recomputed in each iteration?
> >
> > This can be moved outside the loop, since the value doesn't tend to
> change.
> >
> > >
> > > > +
> > > > + /* Try to wait for any previous AUX channel
> > > > + activity
> > > */
> > > > + status = intel_dp_aux_wait_done(intel_dp);
> > >
> > > How does it help to wait here for the same condition that was
> > > already waited for at the end of the loop?
> >
> > Here we are checking for busy bit so as to ensure that the previous
> > transfer is complete and only then the new transfer is initiated.
> >
> > In the latter case, we sent the data and then wait to get the
> > acknowledgement(busy/error/timeout).
> >
> > Check for busy is to be done before sending the data. Here it was done
> > before this loop. The spec limits the trials for sending data to 3 in
> > case of failure and in each of this iteration it has to be started
> > freshly. So we need to ensure that the previous transfer is completed
> > before sending the new data.
>
> Not sure what you mean by "freshly". One potential problem in the current
> code I can see is that if BUSY is still set after
> intel_dp_aux_wait_done() returns none of the control register fields should
> be changed, so I think at that point the transfer should be aborted.
Good Catch! I missed that. Will surely take care of this in the next version.
>
> Also since a while back intel_dp_aux_wait_done() was changed to poll for
> the transfer completion instead of waiting for an interrupt, the
> corresponding interrupt should not be enabled either in the control register.
Yes this is in my TODO list, most likely in my next patch.
Thanks and Regards,
Arun R Murthy
--------------------
>
> > Thanks and Regards,
> > Arun R Murthy
> > --------------------
> > >
> > > > + /* just trace the final value */
> > > > + trace_i915_reg_rw(false, ch_ctl, status,
> > > > + sizeof(status),
> > > true);
> > > > +
> > > > + if (status & DP_AUX_CH_CTL_SEND_BUSY) {
> > > > + drm_WARN(&i915->drm, 1,
> > > > + "%s: not started, previous Tx
> > > > + still in
> > > process (status 0x%08x)\n",
> > > > + intel_dp->aux.name, status);
> > > > + intel_dp->aux_busy_last_status = status;
> > > > + if (try > 3) {
> > > > + ret = -EBUSY;
> > > > + goto out;
> > > > + } else
> > > > + continue;
> > > > + }
> > > >
> > > > - /* Must try at least 3 times according to DP spec */
> > > > - for (try = 0; try < 5; try++) {
> > > > /* Load the send data into the aux channel
> > > > data
> > > registers */
> > > > for (i = 0; i < send_bytes; i += 4)
> > > > intel_de_write(i915, ch_data[i >> 2],
> > > > @@ -
> > > 321,6 +314,7 @@
> > > > intel_dp_aux_xfer(struct intel_dp *intel_dp,
> > > > /* Send the command and wait for it to complete */
> > > > intel_de_write(i915, ch_ctl, send_ctl);
> > > >
> > > > + /* TODO: if typeC then 4.2ms else 800us. For
> > > > + DG2
> > > add 1.5ms for
> > > > +both cases */
> > > > status = intel_dp_aux_wait_done(intel_dp);
> > > >
> > > > /* Clear done status and any errors */
> > > > --
> > > > 2.25.1
> > > >
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