Re: [PATCH] [media] hdpvr: update picture controls to support firmware versions > 0.15

[Janne Grunau <j@jannau.net>]

On Thu, Oct 20, 2011 at 12:35:40PM -0400, Devin Heitmueller wrote:
> On Thu, Oct 20, 2011 at 12:23 PM, Janne Grunau <janne@jannau.net> wrote:
> >
> > I've looked at them only at very beginning and if I recall correctly
> > they had no visible effects. The values in the linux driver were taken
> > from sniffing the windows driver. I remember that I've verified the
> > default brightness value since 0x86 looked odd. I'm not sure that I
> > verified all controls. I might have assumed all controls shared the
> > same value range.
> >
> > There were previous reports of the picture controls not working at all.
> 
> Thanks for taking the time to chime in.

no problem, sorry for ignoring the other mails, I had no time to look
at the problem immediately and then forgot about it.

> If the controls really were broken all along under Linux, then that's
> good to know.  That said, I'm not confident the changes Taylor
> proposed should really be run against older firmwares.  There probably
> needs to be a check to have the values in question only applied if
> firmware >= 16.  If the controls were broken entirely, then we should
> probably not advertise them in ENUM_CTRL and S_CTRL should return
> -EINVAL if running the old firmware (perhaps put a warning in the
> dmesg output saying the controls are unavailable because the user is
> not running firmware >= 16).
> 
> My immediate concern is about ensuring we don't cause breakage in
> older firmware.  For example, we don't know if there are some older
> firmware revisions that *did* work with the driver.  The controls
> might have worked up to firmware revision 10, then been broken from
> 11-15, then work again in 16 (with the new hue value needed).  The
> safe approach is to only use these new settings if they're running
> firmware >= 16.

I think such scenario is unlikely but I don't know it for sure and
I don't want to force anyone to test every firmware version.
Ignoring them for firmware version < 16 should be safe since we assume
they had no effect. Returning -EINVAL might break API-ignoring
applications written with the HD PVR in mind but I think it's a better
approach than silently ignoring those controls.

Janne