Re: [Freedreno] [RFC PATCH v1 01/12] Revert "drm/sysfs: Link DRM connectors to corresponding Type-C connectors"

[Rob Clark]

On Mon, Sep 11, 2023 at 2:15 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
>
> On 06/09/2023 16:38, Heikki Krogerus wrote:
> > On Wed, Sep 06, 2023 at 03:48:35PM +0300, Dmitry Baryshkov wrote:
> >> On Wed, 6 Sept 2023 at 15:44, Heikki Krogerus
> >> <heikki.krogerus@xxxxxxxxxxxxxxx> wrote:
> >>>
> >>> On Tue, Sep 05, 2023 at 01:56:59PM +0300, Dmitry Baryshkov wrote:
> >>>> Hi Heikki,
> >>>>
> >>>> On Tue, 5 Sept 2023 at 11:50, Heikki Krogerus
> >>>> <heikki.krogerus@xxxxxxxxxxxxxxx> wrote:
> >>>>>
> >>>>> Hi Dmitry,
> >>>>>
> >>>>> On Mon, Sep 04, 2023 at 12:41:39AM +0300, Dmitry Baryshkov wrote:
> >>>>>> The kdev->fwnode pointer is never set in drm_sysfs_connector_add(), so
> >>>>>> dev_fwnode() checks never succeed, making the respective commit NOP.
> >>>>>
> >>>>> That's not true. The dev->fwnode is assigned when the device is
> >>>>> created on ACPI platforms automatically. If the drm_connector fwnode
> >>>>> member is assigned before the device is registered, then that fwnode
> >>>>> is assigned also to the device - see drm_connector_acpi_find_companion().
> >>>>>
> >>>>> But please note that even if drm_connector does not have anything in
> >>>>> its fwnode member, the device may still be assigned fwnode, just based
> >>>>> on some other logic (maybe in drivers/acpi/acpi_video.c?).
> >>>>>
> >>>>>> And if drm_sysfs_connector_add() is modified to set kdev->fwnode, it
> >>>>>> breaks drivers already using components (as it was pointed at [1]),
> >>>>>> resulting in a deadlock. Lockdep trace is provided below.
> >>>>>>
> >>>>>> Granted these two issues, it seems impractical to fix this commit in any
> >>>>>> sane way. Revert it instead.
> >>>>>
> >>>>> I think there is already user space stuff that relies on these links,
> >>>>> so I'm not sure you can just remove them like that. If the component
> >>>>> framework is not the correct tool here, then I think you need to
> >>>>> suggest some other way of creating them.
> >>>>
> >>>> The issue (that was pointed out during review) is that having a
> >>>> component code in the framework code can lead to lockups. With the
> >>>> patch #2 in place (which is the only logical way to set kdev->fwnode
> >>>> for non-ACPI systems) probing of drivers which use components and set
> >>>> drm_connector::fwnode breaks immediately.
> >>>>
> >>>> Can we move the component part to the respective drivers? With the
> >>>> patch 2 in place, connector->fwnode will be copied to the created
> >>>> kdev's fwnode pointer.
> >>>>
> >>>> Another option might be to make this drm_sysfs component registration optional.
> >>>
> >>> You don't need to use the component framework at all if there is
> >>> a better way of determining the connection between the DP and its
> >>> Type-C connector (I'm assuming that that's what this series is about).
> >>> You just need the symlinks, not the component.
> >>
> >> The problem is that right now this component registration has become
> >> mandatory. And if I set the kdev->fwnode manually (like in the patch
> >> 2), the kernel hangs inside the component code.
> >> That's why I proposed to move the components to the place where they
> >> are really necessary, e.g. i915 and amd drivers.
> >
> > So why can't we replace the component with the method you are
> > proposing in this series of finding out the Type-C port also with
> > i915, AMD, or whatever driver and platform (that's the only thing that
> > component is used for)?
>
> The drm/msm driver uses drm_bridge for the pipeline (including the last
> DP entry) and the drm_bridge_connector to create the connector. I think
> that enabling i915 and AMD drivers to use drm_bridge fells out of scope
> for this series.
>
>
> > Determining the connection between a DP and its Type-C connector is
> > starting to get really important, so ideally we have a common solution
> > for that.
>
> Yes. This is what we have been discussing with Simon for quite some time
> on #dri-devel.
>
> Unfortunately I think the solution that got merged was pretty much
> hastened in instead of being well-thought. For example, it is also not
> always possible to provide the drm_connector / typec_connector links (as
> you can see from the patch7. Sometimes we can only express that this is
> a Type-C DP connector, but we can not easily point it to the particular
> USB-C port.
>
> So, I'm not sure, how can we proceed here. Currently merged patch breaks
> drm/msm if we even try to use it by setting kdef->fwnode to
> drm_connector->fwnode. The pointed out `drivers/usb/typec/port-mapper.c`
> is an ACPI-only thing, which is not expected to work in a non-ACPI cases.

In these cases we revert and try again next cycle

BR,
-R

>
> --
> With best wishes
> Dmitry
>