[libcamera-devel] [PATCH] libcamera: v4l2device: Obtain device capabilities

[Niklas Söderlund]

Hi Kieran,

Thanks for your work.

On 2019-01-22 19:20:40 +0000, Kieran Bingham wrote:
> The capabilities structure from the kernel can return capabilities of the
> device, or potentially more specific device capabilities.
> 
> Handle this with an inline function to return the correct value.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
> Jacopo,
> 
> Sending this now to see what you think, as it might be useful to consider this
> while you're making adjustments in the area.
> 
> Because this code will be inlined, I expect the compiler to optimise sequential
> uses of this operation where the underlying capabilities is not modified.
> 
> Kieran 
> 
> 
>  src/libcamera/include/v4l2_device.h | 10 +++++++---
>  src/libcamera/v4l2_device.cpp       |  7 +++++++
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h
> index b92e1f1c96c3..90d18b9f2260 100644
> --- a/src/libcamera/include/v4l2_device.h
> +++ b/src/libcamera/include/v4l2_device.h
> @@ -26,10 +26,14 @@ struct V4L2Capability final : v4l2_capability {
>  	{
>  		return reinterpret_cast<const char *>(v4l2_capability::bus_info);
>  	}
> +	unsigned int caps() const
> +	{
> +		return capabilities & V4L2_CAP_DEVICE_CAPS ? device_caps : capabilities;
> +	}

I can't make up my mind if I like this or not :-)

I do see the need for it, something in my thinks this should be handled 
by a macro as to not make it part of the class itself, but maybe that is 
just a force of habit :-)

If you also have considered these things and still feel this is the way 
to go I won't object. I do however think the name is somewhat lacking if 
it's to be part of the class, how about spelling it out capabilities() ?  

>  
> -	bool isCapture() const { return capabilities & V4L2_CAP_VIDEO_CAPTURE; }
> -	bool isOutput() const { return capabilities & V4L2_CAP_VIDEO_OUTPUT; }
> -	bool hasStreaming() const { return capabilities & V4L2_CAP_STREAMING; }
> +	bool isCapture() const { return caps() & V4L2_CAP_VIDEO_CAPTURE; }
> +	bool isOutput() const { return caps() & V4L2_CAP_VIDEO_OUTPUT; }
> +	bool hasStreaming() const { return caps() & V4L2_CAP_STREAMING; }
>  };
>  
>  class MediaEntity;
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index 2b17fa1eb0e8..4d1cc5b6070f 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -49,6 +49,13 @@ LOG_DEFINE_CATEGORY(V4L2)
>   * \return The string containing the device location
>   */
>  
> +/**
> + * \fn unsigned int V4L2Capability::caps()
> + * \brief Retrieve the capabilities of the device
> + * \return The device specific capabilities if V4L2_CAP_DEVICE_CAPS is set or
> + * 	   driver capabilities otherwise
> + */
> +
>  /**
>   * \fn bool V4L2Capability::isCapture()
>   * \brief Identify if the device is capable of capturing video
> -- 
> 2.17.1
> 
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-- 
Regards,
Niklas Söderlund