Re: [PATCHv8 2/2] drm: tda998x: set the connector info

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Wed, Oct 16, 2019 at 03:39:16PM +0200, Hans Verkuil wrote:
> From: Dariusz Marcinkiewicz <darekm@google.com>
> 
> Fill in the cec_connector_info when calling cec_notifier_conn_register().
> 
> Signed-off-by: Dariusz Marcinkiewicz <darekm@google.com>
> Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  drivers/gpu/drm/i2c/tda998x_drv.c | 31 ++++++++++++++++++-------------
>  1 file changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
> index 8262b44b776e..b0620842fa3a 100644
> --- a/drivers/gpu/drm/i2c/tda998x_drv.c
> +++ b/drivers/gpu/drm/i2c/tda998x_drv.c
> @@ -1337,6 +1337,8 @@ static int tda998x_connector_init(struct tda998x_priv *priv,
>  				  struct drm_device *drm)
>  {
>  	struct drm_connector *connector = &priv->connector;
> +	struct cec_connector_info conn_info;
> +	struct cec_notifier *notifier;
>  	int ret;
>  
>  	connector->interlace_allowed = 1;
> @@ -1353,6 +1355,17 @@ static int tda998x_connector_init(struct tda998x_priv *priv,
>  	if (ret)
>  		return ret;
>  
> +	cec_fill_conn_info_from_drm(&conn_info, connector);
> +
> +	notifier = cec_notifier_conn_register(priv->cec_glue.parent,
> +					      NULL, &conn_info);
> +	if (!notifier)
> +		return -ENOMEM;
> +
> +	mutex_lock(&priv->cec_notify_mutex);
> +	priv->cec_notify = notifier;
> +	mutex_unlock(&priv->cec_notify_mutex);

As per my previous comments, this is a single-copy atomic operation.
Either priv->cec_notify is set or it isn't; there is no intermediate
value.  It can't be set to a value until cec_notifier_conn_register()
has completed.  So the lock doesn't help.

> +
>  	drm_connector_attach_encoder(&priv->connector,
>  				     priv->bridge.encoder);
>  
> @@ -1372,6 +1385,11 @@ static void tda998x_bridge_detach(struct drm_bridge *bridge)
>  {
>  	struct tda998x_priv *priv = bridge_to_tda998x_priv(bridge);
>  
> +	mutex_lock(&priv->cec_notify_mutex);
> +	cec_notifier_conn_unregister(priv->cec_notify);
> +	priv->cec_notify = NULL;
> +	mutex_unlock(&priv->cec_notify_mutex);

This is the only case where the lock makes sense - to ensure that any
of the cec_notifier_set_phys_addr*() functions aren't called
concurrently with it.  However, there's no locking around the instance
in tda998x_connector_get_modes(), so have you ensured that that
function can't be called concurrently?

Thanks.

-- 
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