Re: [PATCH v4] drm/msm/dp: add logs across DP driver for ease of debugging

[Stephen Boyd <swboyd@chromium.org>]

Quoting maitreye@codeaurora.org (2021-07-22 20:53:37)
> On 2021-07-22 15:09, Stephen Boyd wrote:
> Thank you for the comments .
> > Quoting maitreye@codeaurora.org (2021-07-22 14:33:43)
> >> Thank you Stephen.
> >>
> >> On 2021-07-22 13:31, Stephen Boyd wrote:
> >> > Quoting maitreye (2021-07-21 16:19:40)
> >> >> From: Maitreyee Rao <maitreye@codeaurora.org>
> >> >>
> >> >> Add trace points across the MSM DP driver to help debug
> >> >> interop issues.
> >> >>
> >> >> Changes in v4:
> >> >>  - Changed goto statement and used if else-if
> >> >
> >> > I think drm likes to see all the changelog here to see patch evolution.
> >> >
> >> Yes, I will fix this
> >> >>
> >> >> Signed-off-by: Maitreyee Rao <maitreye@codeaurora.org>
> >> >> ---
> >> >> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c
> >> >> b/drivers/gpu/drm/msm/dp/dp_link.c
> >> >> index be986da..8c98ab7 100644
> >> >> --- a/drivers/gpu/drm/msm/dp/dp_link.c
> >> >> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> >> >> @@ -1036,43 +1036,28 @@ int dp_link_process_request(struct dp_link
> >> >> *dp_link)
> >> >>
> >> >>         if (link->request.test_requested == DP_TEST_LINK_EDID_READ) {
> >> >>                 dp_link->sink_request |= DP_TEST_LINK_EDID_READ;
> >> >> -               return ret;
> >> >>         }
> >> >> -
> >> >> -       ret = dp_link_process_ds_port_status_change(link);
> >> >> -       if (!ret) {
> >> >> +       else if (!(ret = dp_link_process_ds_port_status_change(link)))
> >> >> {
> >> >>                 dp_link->sink_request |= DS_PORT_STATUS_CHANGED;
> >> >> -               return ret;
> >> >>         }
> >> >> -
> >> >> -       ret = dp_link_process_link_training_request(link);
> >> >> -       if (!ret) {
> >> >> +       else if (!(ret = dp_link_process_link_training_request(link)))
> >> >> {
> >> >>                 dp_link->sink_request |= DP_TEST_LINK_TRAINING;
> >> >> -               return ret;
> >> >>         }
> >> >> -
> >> >> -       ret = dp_link_process_phy_test_pattern_request(link);
> >> >> -       if (!ret) {
> >> >> +       else if (!(ret =
> >> >> dp_link_process_phy_test_pattern_request(link))) {
> >> >>                 dp_link->sink_request |=
> >> >> DP_TEST_LINK_PHY_TEST_PATTERN;
> >> >> -               return ret;
> >> >> -       }
> >> >> -
> >> >> -       ret = dp_link_process_link_status_update(link);
> >> >> -       if (!ret) {
> >> >> +       }
> >> >> +       else if (!(ret = dp_link_process_link_status_update(link))) {
> >> >
> >> > The kernel coding style is to leave the brackets on the same line
> >> >
> >> >       if (condition) {
> >> >
> >> >       } else if (conditon) {
> >> >
> >> >       }
> >> >
> >> > See Documentation/process/coding-style.rst
> >> >
> >> Yes, I will fix this
> >>
> >> > Also, the if (!(ret = dp_link_...)) style is really hard to read. Maybe
> >> > apply this patch before?
> >> >
> >> > ----8<----
> >> > diff --git a/drivers/gpu/drm/msm/dp/dp_link.c
> >> > b/drivers/gpu/drm/msm/dp/dp_link.c
> >> > index 1195044a7a3b..408cddd90f0f 100644
> >> > --- a/drivers/gpu/drm/msm/dp/dp_link.c
> >> > +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> >> > @@ -1027,41 +1027,22 @@ int dp_link_process_request(struct dp_link
> >> > *dp_link)
> >> >
> >> >       if (link->request.test_requested == DP_TEST_LINK_EDID_READ) {
> >> >               dp_link->sink_request |= DP_TEST_LINK_EDID_READ;
> >> > -             return ret;
> >> > -     }
> >> > -
> >> > -     ret = dp_link_process_ds_port_status_change(link);
> >> > -     if (!ret) {
> >> > +     } else if (!dp_link_process_ds_port_status_change(link)) {
> >> >               dp_link->sink_request |= DS_PORT_STATUS_CHANGED;
> >> > -             return ret;
> >> > -     }
> >> > -
> >> > -     ret = dp_link_process_link_training_request(link);
> >> > -     if (!ret) {
> >> > +     } else if (!dp_link_process_link_training_request(link)) {
> >> >               dp_link->sink_request |= DP_TEST_LINK_TRAINING;
> >> > -             return ret;
> >> > -     }
> >> > -
> >> > -     ret = dp_link_process_phy_test_pattern_request(link);
> >> > -     if (!ret) {
> >> > +     } else if (!dp_link_process_phy_test_pattern_request(link)) {
> >> >               dp_link->sink_request |= DP_TEST_LINK_PHY_TEST_PATTERN;
> >> > -             return ret;
> >> > -     }
> >> > -
> >> > -     ret = dp_link_process_link_status_update(link);
> >> > -     if (!ret) {
> >> > +     } else if (!dp_link_process_link_status_update(link)) {
> >> >               dp_link->sink_request |= DP_LINK_STATUS_UPDATED;
> >> > -             return ret;
> >> > -     }
> >> > -
> >> > -     if (dp_link_is_video_pattern_requested(link)) {
> >> > -             ret = 0;
> >> > -             dp_link->sink_request |= DP_TEST_LINK_VIDEO_PATTERN;
> >> > -     }
> >> > +     } else {
> >> > +             if (dp_link_is_video_pattern_requested(link))
> >> > +                     dp_link->sink_request |= DP_TEST_LINK_VIDEO_PATTERN;
> >> >
> >> > -     if (dp_link_is_audio_pattern_requested(link)) {
> >> > -             dp_link->sink_request |= DP_TEST_LINK_AUDIO_PATTERN;
> >> > -             return -EINVAL;
> >> > +             if (dp_link_is_audio_pattern_requested(link)) {
> >> > +                     dp_link->sink_request |= DP_TEST_LINK_AUDIO_PATTERN;
> >> > +                     ret = -EINVAL;
> >> > +             }
> >> >       }
> >> >
> >> >       return ret;
> >> The reason I did this was to preserve the value of ret as the caller
> >> of
> >> the function checks it. Some functions return -EINVAl like in here:
> >> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/msm/dp/dp_link.c#L972
> >> , so to check that it would be necessary to get the ret value.
> >
> > ret is overwritten multiple times. The logic seems to be if ret is
> > not-zero, reassign it, until we get to the end. How about this
> >
> > ----8<----
> > diff --git a/drivers/gpu/drm/msm/dp/dp_link.c
> > b/drivers/gpu/drm/msm/dp/dp_link.c
> > index 1195044a7a3b..e59138566c0a 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_link.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> > @@ -1027,41 +1027,27 @@ int dp_link_process_request(struct dp_link
> > *dp_link)
> >
> >       if (link->request.test_requested == DP_TEST_LINK_EDID_READ) {
> >               dp_link->sink_request |= DP_TEST_LINK_EDID_READ;
> > -             return ret;
> > -     }
> > -
> > -     ret = dp_link_process_ds_port_status_change(link);
> > -     if (!ret) {
> > +     } else if (!dp_link_process_ds_port_status_change(link)) {
> >               dp_link->sink_request |= DS_PORT_STATUS_CHANGED;
> > -             return ret;
> > -     }
> > -
> > -     ret = dp_link_process_link_training_request(link);
> > -     if (!ret) {
> > +     } else if (!dp_link_process_link_training_request(link)) {
> >               dp_link->sink_request |= DP_TEST_LINK_TRAINING;
> > -             return ret;
> > -     }
> > -
> > -     ret = dp_link_process_phy_test_pattern_request(link);
> > -     if (!ret) {
> > +     } else if (!dp_link_process_phy_test_pattern_request(link)) {
> >               dp_link->sink_request |= DP_TEST_LINK_PHY_TEST_PATTERN;
> > -             return ret;
> > -     }
> > -
> > -     ret = dp_link_process_link_status_update(link);
> > -     if (!ret) {
> > -             dp_link->sink_request |= DP_LINK_STATUS_UPDATED;
> > -             return ret;
> > -     }
> > -
> > -     if (dp_link_is_video_pattern_requested(link)) {
> > -             ret = 0;
> > -             dp_link->sink_request |= DP_TEST_LINK_VIDEO_PATTERN;
> > -     }
> > -
> > -     if (dp_link_is_audio_pattern_requested(link)) {
> > -             dp_link->sink_request |= DP_TEST_LINK_AUDIO_PATTERN;
> > -             return -EINVAL;
> > +     } else {
> > +             ret = dp_link_process_link_status_update(link);
> > +             if (!ret) {
> > +                     dp_link->sink_request |= DP_LINK_STATUS_UPDATED;
> > +             } else {
> > +                     if (dp_link_is_video_pattern_requested(link)) {
> > +                             ret = 0;
> > +                             dp_link->sink_request |= DP_TEST_LINK_VIDEO_PATTERN;
> > +                     }
> > +
> > +                     if (dp_link_is_audio_pattern_requested(link)) {
> > +                             dp_link->sink_request |= DP_TEST_LINK_AUDIO_PATTERN;
> > +                             ret = -EINVAL;
> > +                     }
> > +             }
> >       }
> >
> >       return ret;
> I do agree, this will solve the issue for over writing ret variable. But
> I can see two potential problems with this, if we get two events at the
> same time or one of the other we might end up processing the two events,
> which won't be the expected behavior.

The code isn't written to handle this. Does it need to handle it? If so,
please update it for that new feature in a different patch than this one
that adds logging.

>For example, if we get
> dp_link_process_link_status_update and it gives a non zero result and we
> go to the else statement, and get the event for video pattern request,
> we will  end up processing two events.


> The second problem, is currently
> we only have APIs that return 0 or EINVAL as return values, but if we
> ever in future add an API with a different return value it wont be easy
> to add the behavior.

Agreed. Fortunately it's just code and it can easily be rewritten in the
future when it changes.

> But if these issues seem like they can be ignored ,
> then we can go ahead with your suggestions.

I think they can be ignored if we're not supposed to handle two events
at the same time.