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    SubjectRe: [PATCH v4 8/8] drm/nouveau: Call pm_runtime_get_noresume() from hpd handlers
    On Wed, Aug 01, 2018 at 05:14:58PM -0400, Lyude Paul wrote:
    > We can't and don't need to try resuming the device from our hotplug
    > handlers, but hotplug events are generally something we'd like to keep
    > the device awake for whenever possible. So, grab a PM ref safely in our
    > hotplug handlers using pm_runtime_get_noresume() and mark the device as
    > busy once we're finished.

    Patch looks fine in principle, but doesn't seem to be sufficient to fix
    the following race:

    1. runtime_suspend commences
    2. user plugs in a display before the runtime_suspend worker disables
    hotplug interrupts in nouveau_display_fini()
    3. hotplug is handled, display is lit up
    4. runtime_suspend worker waits for hotplug handler to finish
    5. GPU is runtime suspended and the newly plugged in display goes black

    The call to pm_runtime_mark_last_busy() has no effect in this situation
    because rpm_suspend() doesn't look at the last_busy variable after the
    call to rpm_callback(). What's necessary here is that runtime_suspend is
    aborted and -EBUSY returned.

    Thanks,

    Lukas

    >
    > Signed-off-by: Lyude Paul <lyude@redhat.com>
    > Cc: stable@vger.kernel.org
    > Cc: Lukas Wunner <lukas@wunner.de>
    > Cc: Karol Herbst <karolherbst@gmail.com>
    > ---
    > drivers/gpu/drm/nouveau/nouveau_connector.c | 8 ++++++++
    > 1 file changed, 8 insertions(+)
    >
    > diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
    > index 8409c3f2c3a1..5a8e8c1ad647 100644
    > --- a/drivers/gpu/drm/nouveau/nouveau_connector.c
    > +++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
    > @@ -1152,6 +1152,11 @@ nouveau_connector_hotplug(struct nvif_notify *notify)
    > const char *name = connector->name;
    > struct nouveau_encoder *nv_encoder;
    >
    > + /* Resuming the device here isn't possible; but the suspend PM ops
    > + * will wait for us to finish our work before disabling us so this
    > + * should be enough
    > + */
    > + pm_runtime_get_noresume(drm->dev->dev);
    > nv_connector->hpd_task = current;
    >
    > if (rep->mask & NVIF_NOTIFY_CONN_V0_IRQ) {
    > @@ -1171,6 +1176,9 @@ nouveau_connector_hotplug(struct nvif_notify *notify)
    > }
    >
    > nv_connector->hpd_task = NULL;
    > +
    > + pm_runtime_mark_last_busy(drm->dev->dev);
    > + pm_runtime_put_autosuspend(drm->dev->dev);
    > return NVIF_NOTIFY_KEEP;
    > }
    >
    > --
    > 2.17.1
    >

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