On Thu, Jul 04, 2019 at 03:05:12PM -0400, sunpeng.li@xxxxxxx wrote:
> From: Leo Li <sunpeng.li@xxxxxxx>
>
> This can be used to create more descriptive symlinks for MST aux
> devices. Consider the following udev rule:
>
> SUBSYSTEM=="drm_dp_aux_dev", SUBSYSTEMS=="drm", ATTRS{mstpath}=="?*",
> SYMLINK+="drm_dp_aux/by-path/$attr{mstpath}"
>
> The following symlinks will be created (depending on your MST topology):
>
> $ ls /dev/drm_dp_aux/by-path/
> card0-mst:0-1 card0-mst:0-1-1 card0-mst:0-1-8 card0-mst:0-8
>
> Signed-off-by: Leo Li <sunpeng.li@xxxxxxx>
> ---
> drivers/gpu/drm/drm_sysfs.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> index ad10810bc972..53fd1f71e900 100644
> --- a/drivers/gpu/drm/drm_sysfs.c
> +++ b/drivers/gpu/drm/drm_sysfs.c
> @@ -236,16 +236,39 @@ static ssize_t modes_show(struct device *device,
> return written;
> }
>
> +static ssize_t mstpath_show(struct device *device,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct drm_connector *connector = to_drm_connector(device);
> + ssize_t ret = 0;
> + char *path;
> +
> + mutex_lock(&connector->dev->mode_config.mutex);
The blob is populated when the connector is created so I don't think
this lock is actually doing anything for us.
One would also hope that device_unregister() protects us from racing
with the removal of the attribute. Eg. if you hold a file descriptor
open to the sysfs file does device_unregister() block until the fd is
closed?
> + if (!connector->path_blob_ptr)
> + goto unlock;
> +
> + path = connector->path_blob_ptr->data;
> + ret = snprintf(buf, PAGE_SIZE, "card%d-%s\n",
> + connector->dev->primary->index, path);
> +
> +unlock:
> + mutex_unlock(&connector->dev->mode_config.mutex);
> + return ret;
> +}
> +
> static DEVICE_ATTR_RW(status);
> static DEVICE_ATTR_RO(enabled);
> static DEVICE_ATTR_RO(dpms);
> static DEVICE_ATTR_RO(modes);
> +static DEVICE_ATTR_RO(mstpath);
>
> static struct attribute *connector_dev_attrs[] = {
> &dev_attr_status.attr,
> &dev_attr_enabled.attr,
> &dev_attr_dpms.attr,
> &dev_attr_modes.attr,
> + &dev_attr_mstpath.attr,
> NULL
> };
>
> --
> 2.22.0
--
Ville Syrjälä
Intel
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