[PATCH 1/2] drm/edid: Add helper to detect whether EDID changed

[Daniel Vetter]

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