Re: [PATCH v4 9/9] media: uvcvideo: Implement UVC_QUIRK_PRIVACY_DURING_STREAM

[Laurent Pinchart]

Hi Ricardo,

Thank you for the patch.

On Tue, Dec 15, 2020 at 04:44:39PM +0100, Ricardo Ribalda wrote:
> Some devices, can only read the privacy_pin if the device is
> streaming.

:-(

> This patch implement a quirk for such devices, in order to avoid invalid
> reads and/or spurious events.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 97 ++++++++++++++++++++++++++----
>  drivers/media/usb/uvc/uvc_queue.c  |  3 +
>  drivers/media/usb/uvc/uvcvideo.h   |  6 ++
>  3 files changed, 94 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index e49491250e87..61313019e226 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -7,6 +7,7 @@
>   */
>  
>  #include <linux/atomic.h>
> +#include <linux/dmi.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> @@ -1471,13 +1472,39 @@ static int uvc_parse_control(struct uvc_device *dev)
>  	return 0;
>  }
>  
> +static bool uvc_ext_gpio_is_streaming(struct uvc_device *dev)
> +{
> +	struct uvc_streaming *streaming;
> +
> +	list_for_each_entry(streaming, &dev->streams, list) {
> +		if (uvc_queue_streaming(&streaming->queue))
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
> +/* Update the cached value and return true if it has changed */
> +static bool uvc_gpio_update_value(struct uvc_entity *unit, u8 *new_val)
> +{
> +	*new_val = gpiod_get_value(unit->gpio.gpio_privacy);
> +
> +	return atomic_xchg(&unit->gpio.gpio_privacy_value, *new_val) !=
> +								      *new_val;

That's a weird indentation. Also, as the left hand side modifies
*new_val, does C guarantee the order in which the two operands to != are
evaluated ? Could the code be written in an easier to read way ?

> +}
> +
>  static int uvc_gpio_get_cur(struct uvc_device *dev, struct uvc_entity *entity,
>  			    u8 cs, void *data, u16 size)
>  {
>  	if (cs != UVC_CT_PRIVACY_CONTROL || size < 1)
>  		return -EINVAL;
>  
> -	*(uint8_t *)data = gpiod_get_value(entity->gpio.gpio_privacy);
> +	if ((dev->quirks & UVC_QUIRK_PRIVACY_DURING_STREAM) &&
> +	    !uvc_ext_gpio_is_streaming(dev))
> +		return -EBUSY;
> +
> +	uvc_gpio_update_value(entity, (uint8_t *)data);
> +
>  	return 0;
>  }
>  
> @@ -1491,26 +1518,69 @@ static int uvc_gpio_get_info(struct uvc_device *dev, struct uvc_entity *entity,
>  	return 0;
>  }
>  
> -static irqreturn_t uvc_privacy_gpio_irq(int irq, void *data)
> +static struct uvc_entity *uvc_find_ext_gpio_unit(struct uvc_device *dev)
>  {
> -	struct uvc_device *dev = data;
> -	struct uvc_video_chain *chain;
>  	struct uvc_entity *unit;
> -	u8 value;
>  
> -	/* GPIO entities are always on the first chain */
> -	chain = list_first_entry(&dev->chains, struct uvc_video_chain, list);
>  	list_for_each_entry(unit, &dev->entities, list) {
> -		if (UVC_ENTITY_TYPE(unit) != UVC_EXT_GPIO_UNIT)
> -			continue;
> -		value = gpiod_get_value(unit->gpio.gpio_privacy);
> -		uvc_ctrl_status_event(NULL, chain, unit->controls, &value);
> -		return IRQ_HANDLED;
> +		if (UVC_ENTITY_TYPE(unit) == UVC_EXT_GPIO_UNIT)
> +			return unit;
>  	}
>  
> +	return unit;
> +}
> +
> +void uvc_privacy_gpio_event(struct uvc_device *dev)
> +{
> +	struct uvc_entity *unit;
> +	struct uvc_video_chain *chain;
> +	u8 new_value;
> +
> +	unit = uvc_find_ext_gpio_unit(dev);
> +	if (WARN_ONCE(!unit, "Unable to find entity ext_gpio_unit"))
> +		return;
> +
> +	if (!uvc_gpio_update_value(unit, &new_value))
> +		return;

If VIDIOC_G_CTRL() is called before the IRQ is processed, this
uvc_gpio_update_value() call will return false, and no event will be
generated. I don't think that's right, and even should be generated
every time the control changes.

> +
> +	/* GPIO entities are always on the first chain */
> +	chain = list_first_entry(&dev->chains, struct uvc_video_chain, list);
> +	uvc_ctrl_status_event(NULL, chain, unit->controls, &new_value);
> +}
> +
> +static irqreturn_t uvc_privacy_gpio_irq(int irq, void *data)
> +{
> +	struct uvc_device *dev = data;
> +
> +	/* Ignore privacy events during streamoff */
> +	if (dev->quirks & UVC_QUIRK_PRIVACY_DURING_STREAM)
> +		if (!uvc_ext_gpio_is_streaming(dev))
> +			return IRQ_HANDLED;

	if (dev->quirks & UVC_QUIRK_PRIVACY_DURING_STREAM) {
		if (!uvc_ext_gpio_is_streaming(dev))
			return IRQ_HANDLED;
	}

There's a potential race condition with VIDIOC_STREAMON and
VIDIOC_STREAMOFF. Could you explain what the device does exactly when
not streaming ? As the GPIO isn't tied to the UVC controller, how comes
the streaming state influences it ? Any hope the firmware could be fixed
instead ?

> +
> +	uvc_privacy_gpio_event(dev);
> +
>  	return IRQ_HANDLED;
>  }
>  
> +static const struct dmi_system_id privacy_valid_during_streamon[] = {
> +	{
> +		.ident = "HP Elite c1030 Chromebook",
> +		.matches = {
> +			DMI_MATCH(DMI_SYS_VENDOR, "HP"),
> +			DMI_MATCH(DMI_PRODUCT_NAME, "Jinlon"),
> +		},
> +	},
> +	{
> +		.ident = "HP Pro c640 Chromebook",
> +		.matches = {
> +			DMI_MATCH(DMI_SYS_VENDOR, "HP"),
> +			DMI_MATCH(DMI_PRODUCT_NAME, "Dratini"),
> +		},
> +	},
> +	{ } /* terminate list */
> +};
> +
> +
>  static int uvc_parse_gpio(struct uvc_device *dev)
>  {
>  	struct uvc_entity *unit;
> @@ -1545,6 +1615,9 @@ static int uvc_parse_gpio(struct uvc_device *dev)
>  	if (irq == -EPROBE_DEFER)
>  		return -EPROBE_DEFER;
>  
> +	if (dmi_check_system(privacy_valid_during_streamon))
> +		dev->quirks |= UVC_QUIRK_PRIVACY_DURING_STREAM;
> +
>  	if (irq < 0)
>  		return 0;
>  
> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> index cd60c6c1749e..e800d491303f 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -337,9 +337,12 @@ int uvc_dequeue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *buf,
>  int uvc_queue_streamon(struct uvc_video_queue *queue, enum v4l2_buf_type type)
>  {
>  	int ret;
> +	struct uvc_streaming *stream = uvc_queue_to_stream(queue);
>  
>  	mutex_lock(&queue->mutex);
>  	ret = vb2_streamon(&queue->queue, type);
> +	if (stream->dev->quirks & UVC_QUIRK_PRIVACY_DURING_STREAM)
> +		uvc_privacy_gpio_event(stream->dev);
>  	mutex_unlock(&queue->mutex);
>  
>  	return ret;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 2b5ba4b02d3a..2a95b3ed3ea8 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -6,6 +6,7 @@
>  #error "The uvcvideo.h header is deprecated, use linux/uvcvideo.h instead."
>  #endif /* __KERNEL__ */
>  
> +#include <linux/atomic.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/kernel.h>
>  #include <linux/poll.h>
> @@ -209,6 +210,7 @@
>  #define UVC_QUIRK_RESTORE_CTRLS_ON_INIT	0x00000400
>  #define UVC_QUIRK_FORCE_Y8		0x00000800
>  #define UVC_QUIRK_FORCE_BPP		0x00001000
> +#define UVC_QUIRK_PRIVACY_DURING_STREAM	0x00002000
>  
>  /* Format flags */
>  #define UVC_FMT_FLAG_COMPRESSED		0x00000001
> @@ -359,6 +361,7 @@ struct uvc_entity {
>  			u8  bControlSize;
>  			u8  *bmControls;
>  			struct gpio_desc *gpio_privacy;
> +			atomic_t  gpio_privacy_value;
>  		} gpio;
>  	};
>  
> @@ -815,6 +818,9 @@ extern const struct v4l2_file_operations uvc_fops;
>  int uvc_mc_register_entities(struct uvc_video_chain *chain);
>  void uvc_mc_cleanup_entity(struct uvc_entity *entity);
>  
> +/* Privacy gpio */
> +void uvc_privacy_gpio_event(struct uvc_device *dev);
> +
>  /* Video */
>  int uvc_video_init(struct uvc_streaming *stream);
>  int uvc_video_suspend(struct uvc_streaming *stream);

-- 
Regards,

Laurent Pinchart