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    SubjectRe: [PATCH 1/2] drm/edid: Add helper to detect whether EDID changed
    On Mon, Jul 24, 2017 at 05:54:46PM +0300, Paul Kocialkowski wrote:
    > This adds a common drm helper to detect whether the EDID changed from
    > the last known cached one. This is useful help detect that a monitor was
    > changed during a suspend/resume cycle.
    >
    > When that happens (a monitor is replaced by another one during suspend),
    > no hotplug event will be triggered so the change will not be caught at
    > resume time. Detecting that the EDID changed allows detecting it.
    >
    > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@linux.intel.com>

    I can't find the older mails I've typed about this, but the plan we've
    discussed a while back was:
    - Add a generational counter to each connector, maybe even expose it to
    userspace.

    - Increment that counter every time something changed, e.g.
    connector->status in the propbe helpers, or when attaching a new edid
    with the set_edid helper.

    - Tada, no changes needed to drivers, and easily extensible to other
    things than edid!

    Cheers, Daniel
    > ---
    > drivers/gpu/drm/drm_edid.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
    > include/drm/drm_edid.h | 3 +++
    > 2 files changed, 48 insertions(+)
    >
    > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
    > index 6bb6337be920..f6ce8bc2907a 100644
    > --- a/drivers/gpu/drm/drm_edid.c
    > +++ b/drivers/gpu/drm/drm_edid.c
    > @@ -5036,3 +5036,48 @@ static void drm_get_displayid(struct drm_connector *connector,
    > }
    > return;
    > }
    > +
    > +/**
    > + * drm_check_edid_changed - Check whether the EDID changed since the last update
    > + * @connector: connector we're probing
    > + * @adapter: I2C adapter to use for DDC
    > + *
    > + * Check whether the EDID changed since the last time it was updated in the
    > + * drm blob cache.
    > + *
    > + * Return: A boolean indicating whether a change happened or not.
    > + */
    > +bool drm_check_edid_changed(struct drm_connector *connector,
    > + struct i2c_adapter *adapter)
    > +{
    > + struct drm_property_blob *edid_blob;
    > + struct edid *edid_stored;
    > + struct edid *edid_read;
    > + int ret = 0;
    > +
    > + if (!connector->edid_blob_ptr)
    > + return false;
    > +
    > + edid_blob = drm_property_blob_get(connector->edid_blob_ptr);
    > + if (!edid_blob)
    > + return false;
    > +
    > + if (!edid_blob->data || edid_blob->length != sizeof(struct edid))
    > + goto out;
    > +
    > + edid_stored = (struct edid *) edid_blob->data;
    > +
    > + edid_read = drm_get_edid(connector, adapter);
    > + if (!edid_read)
    > + goto out;
    > +
    > + ret = memcmp(edid_stored, edid_read, sizeof(struct edid));
    > +
    > + kfree(edid_read);
    > +
    > +out:
    > + drm_property_blob_put(edid_blob);
    > +
    > + return ret != 0;
    > +}
    > +EXPORT_SYMBOL_GPL(drm_check_edid_changed);
    > diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
    > index 1e1908a6b1d6..593a97b269c3 100644
    > --- a/include/drm/drm_edid.h
    > +++ b/include/drm/drm_edid.h
    > @@ -485,4 +485,7 @@ void drm_edid_get_monitor_name(struct edid *edid, char *name,
    > struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
    > int hsize, int vsize, int fresh,
    > bool rb);
    > +bool drm_check_edid_changed(struct drm_connector *connector,
    > + struct i2c_adapter *adapter);
    > +
    > #endif /* __DRM_EDID_H__ */
    > --
    > 2.13.2
    >
    > _______________________________________________
    > dri-devel mailing list
    > dri-devel@lists.freedesktop.org
    > https://lists.freedesktop.org/mailman/listinfo/dri-devel

    --
    Daniel Vetter
    Software Engineer, Intel Corporation
    http://blog.ffwll.ch

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