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

Ausmus, James
2017-09-20T22:54:01Z

On Wed, Sep 20, 2017 at 3:47 PM, Pandiyan, Dhinakaran
<dhinakaran.pandiyan@intel.com> wrote:
> On Wed, 2017-09-20 at 13:02 -0700, Ausmus, James wrote:
>> On Wed, Sep 20, 2017 at 12:55 PM, Pandiyan, Dhinakaran
>> <dhinakaran.pandiyan@intel.com> wrote:
>> > 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?
>>
>> D'oh! You're right - I completely glossed over the whole " ==
>> DP_DPRX_ESI_LEN" bit - sorry for the noise...
>>
>> >
>> >> 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.
>> >
>>
>> Certainly, but you aren't actually using ret for anything anymore, so
>> the variable can be dropped
>>
>>
>> >
>> >>
>> >> > + if (!handled)
>> >> > + return 0;
>> >> > +
> if (ret)
> DRM_DEBUG_KMS("MST irq_hpd handling failed %d\n", ret);
>
>
> I was thinking of adding something like this, but then the drm helper
> functions _handle_down_rep() and _handle_up_req() only ever return 0. I
> also don't want to get rid of 'ret' because that may make it seem like
> the underlying helpers don't return anything. So, we should either
> change the helpers to return something useful or modify their
> signatures. Both options need a bit more thought.
>
> For now, I guess we could add just the debug message. Let me know what
> you think.

A debug message is better than just ignoring the value - I think
that's a good option until the underlying helpers start returning
anything useful...

>
> -DK
>
>> >> > + 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
>> >> >
>> >>
>> >>
>> >>
>>
>>
>>

--

James Ausmus