[PATCH] drm/sysfs: Expose DRM connector id in each connector sysfs

[Manasi Navare]

Hi Won,

Thanks for the patch, I have now merged to drm-misc-next

Regards
Manasi

On Mon, Apr 17, 2023 at 3:52 PM Manasi Navare <navaremanasi at google.com> wrote:
>
> On Tue, Mar 28, 2023 at 6:45 PM Won Chung <wonchung at google.com> wrote:
> >
> > Expose DRM connector id in device sysfs so that we can map the connector
> > id to the connector syspath. Currently, even if we can derive the
> > connector id from modeset, we do not have a way to find the
> > corresponding connector's syspath.
> >
> > This is helpful when determining the root connector of MST tree. When a
> > tree of multiple MST hub is connected to the system, modeset describes
> > the tree in the PATH blob. For example, consider the following scenario.
> >
> > +-------------+
> > | Source      |    +-------------+
> > | (Device)    |    | BranchX     |
> > |             |    | (MST)       |
> > |       [conn6]--->|       [port1]--->DisplayA
> > +-------------+    |             |
> >                    |             |    +-------------+
> >                    |             |    | BranchY     |
> >                    |             |    | (MST)       |
> >                    |       [port2]--->|       [port1]----->DisplayB
> >                    +-------------+    |             |
> >                                       |       [port2]----->DisplayC
> >                                       +-------------+
> >
> > DPMST connector of DisplayA would have "mst:6-1" PATH.
> > DPMST connector of DisplayB would have "mst:6-2-1" PATH.
> > DPMST connector of DisplayC would have "mst:6-2-2" PATH.
> >
> > Given that connector id of 6 is the root of the MST connector tree, we
> > can utilize this patch to parse through DRM connectors sysfs and find
> > which connector syspath corresponds to the root connector (id == 6).
> >
> > ChromeOS intend to use this information for metrics collection. For
> > example, we want to tell which port is deriving which displays even with
> > a MST hub. Chromium patch for parsing DRM connector id from the kernel
> > is at http://crrev.com/c/4317207.
> >
> > Signed-off-by: Won Chung <wonchung at google.com>
>
> Exposing connector id in device sysfs looks good to me.
>
> Reviewed-by: Manasi Navare <navaremanasi at chromium.org>
>
> Manasi
>
> > ---
> >  drivers/gpu/drm/drm_sysfs.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> > index 183130355997..11f98c5d6103 100644
> > --- a/drivers/gpu/drm/drm_sysfs.c
> > +++ b/drivers/gpu/drm/drm_sysfs.c
> > @@ -282,16 +282,27 @@ static ssize_t modes_show(struct device *device,
> >         return written;
> >  }
> >
> > +static ssize_t connector_id_show(struct device *device,
> > +                                struct device_attribute *attr,
> > +                                char *buf)
> > +{
> > +       struct drm_connector *connector = to_drm_connector(device);
> > +
> > +       return sysfs_emit(buf, "%d\n", connector->base.id);
> > +}
> > +
> >  static DEVICE_ATTR_RW(status);
> >  static DEVICE_ATTR_RO(enabled);
> >  static DEVICE_ATTR_RO(dpms);
> >  static DEVICE_ATTR_RO(modes);
> > +static DEVICE_ATTR_RO(connector_id);
> >
> >  static struct attribute *connector_dev_attrs[] = {
> >         &dev_attr_status.attr,
> >         &dev_attr_enabled.attr,
> >         &dev_attr_dpms.attr,
> >         &dev_attr_modes.attr,
> > +       &dev_attr_connector_id.attr,
> >         NULL
> >  };
> >
> > --
> > 2.40.0.348.gf938b09366-goog
> >