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

Ausmus, James
2017-09-20T20:02:56Z

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;
>> > +
>> > + 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