linux-kernel - Re: [PATCH v4 3/6] drm/dsi: Try to match non-DT dsi devices

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Message-ID: <20160121160514.GC647@ulmo.nvidia.com>
Date:	Thu, 21 Jan 2016 17:05:15 +0100
From:	Thierry Reding <treding@...dia.com>
To:	Archit Taneja <architt@...eaurora.org>
CC:	<dri-devel@...ts.freedesktop.org>, <a.hajda@...sung.com>,
	<jani.nikula@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<airlied@...ux.ie>, <daniel@...ll.ch>, <l.stach@...gutronix.de>,
	<robh@...nel.org>, <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] drm/dsi: Try to match non-DT dsi devices

On Thu, Dec 10, 2015 at 06:11:37PM +0530, Archit Taneja wrote:
> Add a device name field in mipi_dsi_device. This name is different from
> the actual dev name (which is of the format "hostname.reg"). When the
> device is created via DT, this name is set to the modalias string.

Why? What's the use of setting this to the modalias string?

> In the non-DT case, the driver creating the DSI device provides the
> name by populating a filed in mipi_dsi_device_info.
> 
> Matching for DT case would be as it was before. For the non-DT case,
> we compare the device and driver names. Other buses (like i2c/spi)

"I2C" and "SPI", please.

> perform a non-DT match by comparing the device name and entries in the
> driver's id_table. Such a mechanism isn't used for the dsi bus.

"DSI", please.

> 
> Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> Signed-off-by: Archit Taneja <architt@...eaurora.org>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c | 25 ++++++++++++++++++++++++-
>  include/drm/drm_mipi_dsi.h     |  6 ++++++
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 9434585..5a46802 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -45,9 +45,26 @@
>   * subset of the MIPI DCS command set.
>   */
>  
> +static const struct device_type mipi_dsi_device_type;
> +
>  static int mipi_dsi_device_match(struct device *dev, struct device_driver *drv)
>  {
> -	return of_driver_match_device(dev, drv);
> +	struct mipi_dsi_device *dsi;
> +
> +	if (dev->type == &mipi_dsi_device_type)
> +		dsi = to_mipi_dsi_device(dev);
> +	else
> +		return 0;

I think this check is redundant. I'm not aware of any case where the bus
->match() callback is called on a device that isn't on said bus.

> +	/* attempt OF style match */
> +	if (of_driver_match_device(dev, drv))
> +		return 1;
> +
> +	/* compare dsi device and driver names */

"DSI", please.

> +	if (!strcmp(dsi->name, drv->name))
> +		return 1;
> +
> +	return 0;
>  }
>  
>  static const struct dev_pm_ops mipi_dsi_device_pm_ops = {
> @@ -125,6 +142,7 @@ struct mipi_dsi_device *mipi_dsi_device_new(struct mipi_dsi_host *host,
>  	dsi->dev.type = &mipi_dsi_device_type;
>  	dsi->dev.of_node = info->node;
>  	dsi->channel = info->reg;
> +	strlcpy(dsi->name, info->type, sizeof(dsi->name));

Don't you need to check info->type != NULL before doing this?

>  
>  	dev_set_name(&dsi->dev, "%s.%d", dev_name(host->dev), info->reg);
>  
> @@ -148,6 +166,11 @@ of_mipi_dsi_device_add(struct mipi_dsi_host *host, struct device_node *node)
>  	int ret;
>  	u32 reg;
>  
> +	if (of_modalias_node(node, info.type, sizeof(info.type)) < 0) {
> +		dev_err(dev, "modalias failure on %s\n", node->full_name);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
>  	ret = of_property_read_u32(node, "reg", &reg);
>  	if (ret) {
>  		dev_err(dev, "device node %s has no valid reg property: %d\n",
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 90f4f3c..cb084af 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -139,8 +139,11 @@ enum mipi_dsi_pixel_format {
>  	MIPI_DSI_FMT_RGB565,
>  };
>  
> +#define DSI_DEV_NAME_SIZE		20
> +
>  /**
>   * struct mipi_dsi_device_info - template for creating a mipi_dsi_device
> + * @type: dsi peripheral chip type
>   * @reg: DSI virtual channel assigned to peripheral
>   * @node: pointer to OF device node
>   *
> @@ -148,6 +151,7 @@ enum mipi_dsi_pixel_format {
>   * DSI device
>   */
>  struct mipi_dsi_device_info {
> +	char type[DSI_DEV_NAME_SIZE];

Why limit ourselves to 20 characters? And why even so complicated? Isn't
the type always static when someone specifies this? Couldn't we simply
use a const char *name here instead?

Thierry

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