linux-kernel - Re: [RFC 2/2] drm/dsi: Get DSI host by DT device node

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Message-id: <55D4425F.4050806@samsung.com>
Date:	Wed, 19 Aug 2015 10:46:23 +0200
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Archit Taneja <architt@...eaurora.org>,
	dri-devel@...ts.freedesktop.org
Cc:	linux-arm-msm@...r.kernel.org, treding@...dia.com,
	inki.dae@...sung.com, linux-kernel@...r.kernel.org,
	airlied@...ux.ie, daniel@...ll.ch, jani.nikula@...ux.intel.com
Subject: Re: [RFC 2/2] drm/dsi: Get DSI host by DT device node

On 06/30/2015 07:24 AM, Archit Taneja wrote:
> mipi_dsi_devices are inherently aware of their host because they
> share a parent-child hierarchy in the device tree.
>
> Non-dsi drivers that create a dummy dsi device don't have this data.
> In order to get this information, they require to a phandle to the dsi
> host in the device tree.
>
> Maintain a list of all the hosts DSI that are currently registered.
>
> This list will be used to find the mipi_dsi_host corresponding to the
> device_node passed in of_find_mipi_dsi_host_by_node.

The lock protects only the list, there is no guarantee that mipi_dsi_host
returned by of_find_mipi_dsi_host_by_node is still valid, or will be valid long
enough.

But this issue affects many kernel frameworks so I am not sure if it should
block this
particular patch.

Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>

Regards
Andrzej

>
> Signed-off-by: Archit Taneja <architt@...eaurora.org>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c | 30 ++++++++++++++++++++++++++++++
>  include/drm/drm_mipi_dsi.h     |  2 ++
>  2 files changed, 32 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 9bfe215..81ddb73 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -239,6 +239,28 @@ struct mipi_dsi_device *mipi_dsi_new_dummy(struct mipi_dsi_host *host, u32 reg)
>  	return dsi;
>  }
>  
> +static DEFINE_MUTEX(host_lock);
> +static LIST_HEAD(host_list);
> +
> +struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node)
> +{
> +	struct mipi_dsi_host *host;
> +
> +	mutex_lock(&host_lock);
> +
> +	list_for_each_entry(host, &host_list, list) {
> +		if (host->dev->of_node == node) {
> +			mutex_unlock(&host_lock);
> +			return host;
> +		}
> +	}
> +
> +	mutex_unlock(&host_lock);
> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(of_find_mipi_dsi_host_by_node);
> +
>  int mipi_dsi_host_register(struct mipi_dsi_host *host)
>  {
>  	struct device_node *node;
> @@ -250,6 +272,10 @@ int mipi_dsi_host_register(struct mipi_dsi_host *host)
>  		of_mipi_dsi_device_add(host, node);
>  	}
>  
> +	mutex_lock(&host_lock);
> +	list_add_tail(&host->list, &host_list);
> +	mutex_unlock(&host_lock);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(mipi_dsi_host_register);
> @@ -266,6 +292,10 @@ static int mipi_dsi_remove_device_fn(struct device *dev, void *priv)
>  void mipi_dsi_host_unregister(struct mipi_dsi_host *host)
>  {
>  	device_for_each_child(host->dev, NULL, mipi_dsi_remove_device_fn);
> +
> +	mutex_lock(&host_lock);
> +	list_del_init(&host->list);
> +	mutex_unlock(&host_lock);
>  }
>  EXPORT_SYMBOL(mipi_dsi_host_unregister);
>  
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index d06ba99..1684a0e 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -100,10 +100,12 @@ struct mipi_dsi_host_ops {
>  struct mipi_dsi_host {
>  	struct device *dev;
>  	const struct mipi_dsi_host_ops *ops;
> +	struct list_head list;
>  };
>  
>  int mipi_dsi_host_register(struct mipi_dsi_host *host);
>  void mipi_dsi_host_unregister(struct mipi_dsi_host *host);
> +struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node);
>  
>  /* DSI mode flags */
>  

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