Re: [PATCH 4/5] drm/i915/dp: Clean up intel_dp_check_mst_status

Pandiyan, Dhinakaran
2017-09-20T19:55:56Z

On Wed, 2017-09-20 at 12:11 -0700, Ausmus, James wrote:
> On Mon, Sep 18, 2017 at 3:21 PM, Dhinakaran Pandiyan
> <dhinakaran.pandiyan@intel.com> wrote:
> > Rewriting this code without the goto, I believe, makes it more readable.
> > One functional change that has been included is the handling of failed ESI
> > register reads. Instead of disabling MST only for the first failed read, we
> > now disable MST on subsequent failed reads too. A failed ESI read is
> > problematic irrespective of whether it is the first or not.
> >
> > Cc: James Ausmus <james.ausmus@intel.com>
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > ---
> > drivers/gpu/drm/i915/intel_dp.c | 75 +++++++++++++++++------------------------
> > 1 file changed, 31 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 98e7b96ca826..cc129aa444ac 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4191,57 +4191,44 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
> > static int
> > intel_dp_check_mst_status(struct intel_dp *intel_dp)
> > {
> > - bool bret;
> > + u8 esi[DP_DPRX_ESI_LEN] = { 0 };
> > + struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> >
> > - if (intel_dp->is_mst) {
> > - u8 esi[DP_DPRX_ESI_LEN] = { 0 };
> > - int ret = 0;
> > - int retry;
> > + if (!intel_dp->is_mst)
> > + return -EINVAL;
> > +
> > + while (intel_dp_get_sink_irq_esi(intel_dp, esi)) {
>
> It looks like if the underlying drm_dp_dpcd_read fails and returns
> -EIO, for instance, you'll get true back from
> intel_dp_get_sink_irq_esi,

Wait, anything other than 14 from that dpcd read is a false, isn't it?

> and you'll still go in to the while, but
> with a potentially invalid esi. Granted, this is a problem in the
> original code as well, but it seems like something that should be
> fixed during the refactoring.
>
>
> > + int ret, retry;
> > bool handled;
> > - bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
> > -go_again:
> > - if (bret == true) {
> > -
> > - /* check link status - esi[10] = 0x200c */
> > - if (intel_dp->active_mst_links &&
> > - !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> > - DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
> > - intel_dp_start_link_train(intel_dp);
> > - intel_dp_stop_link_train(intel_dp);
> > - }
> >
> > - DRM_DEBUG_KMS("got esi %3ph\n", esi);
> > - ret = drm_dp_mst_hpd_irq(&intel_dp->mst_mgr, esi, &handled);
> > -
> > - if (handled) {
> > - for (retry = 0; retry < 3; retry++) {
> > - int wret;
> > - wret = drm_dp_dpcd_write(&intel_dp->aux,
> > - DP_SINK_COUNT_ESI+1,
> > - &esi[1], 3);
> > - if (wret == 3) {
> > - break;
> > - }
> > - }
> > + DRM_DEBUG_KMS("ESI %3ph\n", esi);
> >
> > - bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
> > - if (bret == true) {
> > - DRM_DEBUG_KMS("got esi2 %3ph\n", esi);
> > - goto go_again;
> > - }
> > - } else
> > - ret = 0;
> > + /* check link status - esi[10] = 0x200c */
> > + if (intel_dp->active_mst_links &&
> > + !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> > + intel_dp_start_link_train(intel_dp);
> > + intel_dp_stop_link_train(intel_dp);
> > + }
> >
> > - return ret;
> > - } else {
> > - struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> > - DRM_DEBUG_KMS("failed to get ESI - device may have failed\n");
> > - intel_dp->is_mst = false;
> > - drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp->is_mst);
> > - /* send a hotplug event */
> > - drm_kms_helper_hotplug_event(intel_dig_port->base.base.dev);
> > + ret = drm_dp_mst_hpd_irq(&intel_dp->mst_mgr, esi, &handled);
>
> You're no longer using the value returned by drm_dp_mst_hpd_irq

The way the code was originally written, the return from
drm_dp_mst_hpd_irq() was
a) changed to 0 when handled == false
b) discarded and a new return value was obtained if handled == true and
intel_dp_get_sink_irq_esi() is true the second time.

So the only case when the return value was returned back to the caller
is when handled == true and the second intel_dp_get_sink_irq_esi()
returned false.

But this does not make sense. If the second intel_dp_get_sink_irq_esi()
is false, then we should still have to disable MST. This is the
functional change I noted in the commit message.

>
> > + if (!handled)
> > + return 0;
> > +
> > + for (retry = 0; retry < 3; retry++) {
> > + int wret;
> > +
> > + wret = drm_dp_dpcd_write(&intel_dp->aux,
> > + DP_SINK_COUNT_ESI + 1, &esi[1],
> > + 3);
> > + if (wret == 3)
> > + break;
> > }
> > }
> > +
> > + DRM_DEBUG_KMS("failed to get ESI - device may have failed\n");
> > + intel_dp->is_mst = false;
> > + drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp->is_mst);
> > + drm_kms_helper_hotplug_event(intel_dig_port->base.base.dev);
> > return -EINVAL;
> > }
> >
> > --
> > 2.11.0
> >
>
>
>