Re: [PATCH v2 2/2] s5p-fimc: Add support for alpha component configuration

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

On 11/28/2011 12:42 PM, Hans Verkuil wrote:
> On Friday 25 November 2011 16:39:32 Sylwester Nawrocki wrote:
>> On Exynos SoCs the FIMC IP allows to configure globally the alpha
>> component of all pixels for V4L2_PIX_FMT_RGB32, V4L2_PIX_FMT_RGB555
>> and V4L2_PIX_FMT_RGB444 image formats. This patch adds a v4l2 control
>> in order to let the applications control the alpha component value.
>>
>> The alpha value range depends on the pixel format, for RGB32 it's
>> 0..255 (8-bits), for RGB555 - 0..1 (1-bit) and for RGB444 - 0..15
>> (4-bits). The v4l2 control range is always 0..255 and the alpha
>> component data width is determined by currently set format on the
>> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE buffer queue. The applications
>> need to match the alpha channel data width and the pixel format
>> since the driver will ignore the alpha component bits that are not
>> applicable to the configured pixel format.
> 
> Will the driver ignore the least significant bits or the most significant 
> bits?

Most significant bits will be ignored, i.e. depending on fourcc the valid
alpha bits are:

V4L2_PIX_FMT_RGB555 - [0]
V4L2_PIX_FMT_RGB444 - [3:0]
V4L2_PIX_FMT_RGB32  - [7:0]

--

Regards,
Sylwester