[PATCH v4] drm/msm/dpu1: don't choke on disabling the writeback connector

[Dmitry Baryshkov]

On Mon, 9 Dec 2024 at 21:54, Abhinav Kumar <quic_abhinavk at quicinc.com> wrote:
>
>
>
> On 12/9/2024 2:04 AM, Dmitry Baryshkov wrote:
> > During suspend/resume process all connectors are explicitly disabled and
> > then reenabled. However resume fails because of the connector_status check:
> >
> > [dpu error]connector not connected 3
> > [drm:drm_mode_config_helper_resume [drm_kms_helper]] *ERROR* Failed to resume (-22)
> >
> > It doesn't make sense to check for the Writeback connected status (and
> > other drivers don't perform such check), so drop the check.
> >
> > It wasn't a problem before the commit 71174f362d67 ("drm/msm/dpu: move
> > writeback's atomic_check to dpu_writeback.c"), since encoder's
> > atomic_check() is called under a different conditions that the
> > connector's atomic_check() (e.g. it is not called if there is no
> > connected CRTC or if the corresponding connector is not a part of the
> > new state).
> >
> > Fixes: 71174f362d67 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
> > Cc: stable at vger.kernel.org
> > Reported-by: Leonard Lausen <leonard at lausen.nl>
> > Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/57
> > Tested-by: Leonard Lausen <leonard at lausen.nl> # on sc7180 lazor
> > Reported-by: György Kurucz <me at kuruczgy.com>
> > Link: https://lore.kernel.org/all/b70a4d1d-f98f-4169-942c-cb9006a42b40@kuruczgy.com/
> > Reported-by: Johan Hovold <johan+linaro at kernel.org>
> > Link: https://lore.kernel.org/all/ZzyYI8KkWK36FfXf@hovoldconsulting.com/
> > Tested-by: György Kurucz <me at kuruczgy.com>
> > Reviewed-by: Johan Hovold <johan+linaro at kernel.org>
> > Tested-by: Johan Hovold <johan+linaro at kernel.org>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> > ---
> > Leonard Lausen reported an issue with suspend/resume of the sc7180
> > devices. Fix the WB atomic check, which caused the issue.
> > ---
> > Changes in v4:
> > - Epanded commit message (Johan)
> > - Link to v3: https://lore.kernel.org/r/20241208-dpu-fix-wb-v3-1-a1de69ce4a1b@linaro.org
> >
> > Changes in v3:
> > - Rebased on top of msm-fixes
> > - Link to v2: https://lore.kernel.org/r/20240802-dpu-fix-wb-v2-0-7eac9eb8e895@linaro.org
> >
> > Changes in v2:
> > - Reworked the writeback to just drop the connector->status check.
> > - Expanded commit message for the debugging patch.
> > - Link to v1: https://lore.kernel.org/r/20240709-dpu-fix-wb-v1-0-448348bfd4cb@linaro.org
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > index 16f144cbc0c986ee266412223d9e605b01f9fb8c..8ff496082902b1ee713e806140f39b4730ed256a 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > @@ -42,9 +42,6 @@ static int dpu_wb_conn_atomic_check(struct drm_connector *connector,
> >       if (!conn_state || !conn_state->connector) {
> >               DPU_ERROR("invalid connector state\n");
> >               return -EINVAL;
> > -     } else if (conn_state->connector->status != connector_status_connected) {
> > -             DPU_ERROR("connector not connected %d\n", conn_state->connector->status);
> > -             return -EINVAL;
> >       }
>
> Can you please explain me about why the status was not already connected?
>
> In all the places I checked (unless I missed something), if the detect()
> callback is not registered, the connector is assumed connected like below:
>
> 404     if (funcs->detect_ctx)
> 405             ret = funcs->detect_ctx(connector, ctx, force);
> 406     else if (connector->funcs->detect)
> 407             ret = connector->funcs->detect(connector, force);
> 408     else
> 409             ret = connector_status_connected;
>
> We do not register .detect for WB as WB connector should be always
> connected.
>
> What scenario or use-case is making the connector status to something
> other than connected?
>
> The places which mark the connector as unknown seem to be covered by
> warnings in drm_probe_helper.c but the bug report doesnt seem to be
> hitting those.

Because nobody asks for the getconnector on that connector. For
example,drm_client_for_each_connector_iter() explicitly skips
WRITEBACK connectors. So, drm_client_modeset_probe() also doesn't
request ->fill_modes() on that connector.

I'm almost sure that if somebody runs a `modetest -ac` on the
unpatched kernel after boot, there will be no suspend-related issues.
In fact, I've just checked on RB5.
/sys/class/drm/card0-Writeback-1/status reports 'unknown' before and
'connected' afterwards. You can easily replicate that on your
hardware.

>
> I am wondering if there is some case in fwk resetting this to unknown
> silently (which is incorrect) and perhaps other drivers dont hit this as
> there is a .detect registered which always returns connected and MSM
> should follow that.
>
> 111 static enum drm_connector_status
> 112 komeda_wb_connector_detect(struct drm_connector *connector, bool force)
> 113 {
> 114     return connector_status_connected;
> 115 }
> 116

No, that won't help. You can add a detect() callback and verify that
simply isn't getting called. It's not resetting the connector->status,
it's nobody setting it for the first time.

> >
> >       crtc = conn_state->crtc;
> >
> > ---
> > base-commit: 86313a9cd152330c634b25d826a281c6a002eb77
> > change-id: 20240709-dpu-fix-wb-6cd57e3eb182
> >
> > Best regards,



-- 
With best wishes
Dmitry