On 09.06.2010 20:13, Dave P wrote:
> On Tuesday 08 Jun 2010, VDR User wrote:
>> I'm not sure what FE_CAN_QAM_AUTO is supposed to represent exactly so
>> the problem may not be in VDR, but rather your cards driver not
>> accurately reporting it's capabilities. In which case, the driver
>> needs to be fixed of course.
>
> The card is a Twinhan DST DVB-T using the bttv driver. I'm not an expert at
> reading kernel source, but in drivers/media/dvb/bt8xx/dst.c it does seem
> that FE_CAN_QAM_AUTO is unconditionally set. The card documentation
> doesn't specify whether the device can in fact handle all possible QAM
> settings.
My understanding of the FE_CAN_QAM_... flags is that the driver must
tell the application which modulations it can handle. If FE_CAN_QAM_AUTO
is set, the application doesn't need to tell the driver which modulation
to use, because the driver (or better: the device) can detect it automatically.
If a driver only sets FE_CAN_QAM_AUTO, the applications can't know which of the
various modulations the device can actually handle. I don't think that
FE_CAN_QAM_AUTO is a synonym for "can handle *all* modulations".
The simplest fix (if it is unknown which modulations the device can actually
handle) is probably to set all FE_CAN_QAM_... flags in the driver.
Your patch is not a solution, only a workaround. It would prevent drivers
that can actually handle only a subset of modulations, but do have "auto"
capability, from being properly handled by the application.
Klaus
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