Re: [PATCH 3/5] dvb_frontend: do not allow statistic IOCTLs when sleeping

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 15-08-2012 21:28, Antti Palosaari escreveu:
> Demodulator cannot perform statistic IOCTLs when it is not tuned.
> Return -EAGAIN in such case.
> 
> Signed-off-by: Antti Palosaari <crope@iki.fi>
> ---
>  drivers/media/dvb-core/dvb_frontend.c | 34 +++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
> index 2bc80b1..7d079fb 100644
> --- a/drivers/media/dvb-core/dvb_frontend.c
> +++ b/drivers/media/dvb-core/dvb_frontend.c
> @@ -2132,27 +2132,43 @@ static int dvb_frontend_ioctl_legacy(struct file *file,
>  			err = fe->ops.read_status(fe, status);
>  		break;
>  	}
> +
>  	case FE_READ_BER:
> -		if (fe->ops.read_ber)
> -			err = fe->ops.read_ber(fe, (__u32*) parg);
> +		if (fe->ops.read_ber) {
> +			if (fepriv->thread)
> +				err = fe->ops.read_ber(fe, (__u32 *) parg);
> +			else
> +				err = -EAGAIN;
> +		}
>  		break;
>  


>  	case FE_READ_SIGNAL_STRENGTH:
> -		if (fe->ops.read_signal_strength)
> -			err = fe->ops.read_signal_strength(fe, (__u16*) parg);
> +		if (fe->ops.read_signal_strength) {
> +			if (fepriv->thread)
> +				err = fe->ops.read_signal_strength(fe, (__u16 *) parg);
> +			else
> +				err = -EAGAIN;
> +		}
>  		break;

This one doesn't look right, as the frontend can be able to get the signal strength
at the analog part (afaik, most DVB-S frontends do that). Also, some drivers just
map it to the tuner RF strength.

The proper approach for it is to break signal strength into two different statistics:
	- analog RF strength;
	- signal strength at the demod, after having demod locked.

It makes sense to return -EAGAIN for the second case, but doing it for the first case
is bad, as the RF strength can be used on DVB-S devices, in order to fine-adjust the 
antenna position.

Regards,
Mauro.