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SubjectRe: [PATCH] staging/vc04_services/bcm2835-camera: distinct numeration and names for devices
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Hi Michael, Kay,

On 12/6/19 9:54 AM, Michael Kupfer wrote:
> Create a static atomic counter for numerating cameras.
> Use the Media Subsystem Kernel Internal API to create distinct
> device-names, so that the camera-number (given by the counter)
> matches the camera-name.
>
> Co-developed-by: Kay Friedrich <kay.friedrich@fau.de>
> Signed-off-by: Kay Friedrich <kay.friedrich@fau.de>
> Signed-off-by: Michael Kupfer <michael.kupfer@fau.de>
> ---
> .../vc04_services/bcm2835-camera/bcm2835-camera.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> index beb6a0063bb8..be5f90a8b49d 100644
> --- a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> +++ b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> @@ -60,6 +60,9 @@ MODULE_PARM_DESC(max_video_width, "Threshold for video mode");
> module_param(max_video_height, int, 0644);
> MODULE_PARM_DESC(max_video_height, "Threshold for video mode");
>
> +/* camera instance counter */
> +static atomic_t camera_instance = ATOMIC_INIT(0);
> +
> /* global device data array */
> static struct bm2835_mmal_dev *gdev[MAX_BCM2835_CAMERAS];
>
> @@ -1870,7 +1873,6 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
>
> /* v4l2 core mutex used to protect all fops and v4l2 ioctls. */
> mutex_init(&dev->mutex);
> - dev->camera_num = camera;
> dev->max_width = resolutions[camera][0];
> dev->max_height = resolutions[camera][1];
>
> @@ -1886,8 +1888,9 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
> dev->capture.fmt = &formats[3]; /* JPEG */
>
> /* v4l device registration */
> - snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
> - "%s", BM2835_MMAL_MODULE_NAME);
> + dev->camera_num = v4l2_device_set_name(&dev->v4l2_dev,
> + BM2835_MMAL_MODULE_NAME,
> + &camera_instance);
> ret = v4l2_device_register(NULL, &dev->v4l2_dev);
> if (ret) {
> dev_err(&pdev->dev, "%s: could not register V4L2 device: %d\n",
>

Actually, in this specific case I would not use v4l2_device_set_name().

Instead just use:

snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
"%s-%u", BM2835_MMAL_MODULE_NAME, camera);

It would be even better if there would be just one top-level v4l2_device used
for all the camera instances. After all, there really is just one platform
device for all of the cameras, and I would expect to see just a single
v4l2_device as well.

It doesn't hurt to have multiple v4l2_device structs, but it introduces a
slight memory overhead since one would have been sufficient.

v4l2_device_set_name() is meant for pci-like devices. And it really
is a bit overkill to have it as a helper function.

Regards,

Hans

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