Re: [PATCH 05/12] video/hdmi: Don't let the user of this API create invalid infoframes

Thierry Reding
2013-08-15T14:44:09Z

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On Wed, Aug 14, 2013 at 06:19:08PM +0100, Damien Lespiau wrote:
> To set the active aspect ratio value in the AVI infoframe today, you not
> only have to set the active_aspect field, but also the active_info_valid
> bit. Out of the 1 user of this API, we had 100% misuse, forgetting the
> _valid bit. This was fixed in:
>
> Author: Damien Lespiau <damien.lespiau@intel.com>
> Date: Tue Aug 6 20:32:17 2013 +0100
>
> drm: Don't generate invalid AVI infoframes for CEA modes
>
> We can do better and derive the _valid bit from the user wanting to set
> the active aspect ratio.
[...]
> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
[...]
> @@ -96,7 +96,9 @@ ssize_t hdmi_avi_infoframe_pack(struct hdmi_avi_infoframe *frame, void *buffer,
>
> ptr[0] = ((frame->colorspace & 0x3) << 5) | (frame->scan_mode & 0x3);
>
> - if (frame->active_info_valid)
> + /* Data byte 1, bit 4 has to be set if we provide the active format
> + * aspect ratio */

Nit: According to the coding style rules this should be:

/*
* Data byte 1, ...
* ... ratio.
*/

> + if (frame->active_aspect & 0xf)
> ptr[0] |= BIT(4);
>
> if (frame->horizontal_bar_valid)
> diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
> index bc6743e..931474c6 100644
> --- a/include/linux/hdmi.h
> +++ b/include/linux/hdmi.h
> @@ -109,7 +109,6 @@ struct hdmi_avi_infoframe {
> unsigned char version;
> unsigned char length;
> enum hdmi_colorspace colorspace;
> - bool active_info_valid;

When I initially came up with these data structure I wanted them to
explicitly expose all the fields that CEA/HDMI specifies. The idea was
that a user would actually be allowed to generate invalid infoframes if
they chose to by modifying the hdmi_avi_infoframe structure directly.

Instead I'd prefer to see this handled by some higher level function.

Thierry

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