Re: [PATCH] si2157: Fix DVB-C bandwidth.

[Mauro Carvalho Chehab <m.chehab@samsung.com>]

Em Tue, 22 Jul 2014 12:09:48 +0100
Luis Alves <ljalvs@gmail.com> escreveu:

> This patch fixes DVB-C reception.
> Without setting the bandwidth to 8MHz the received stream gets corrupted.
> 
> Regards,
> Luis
> 
> Signed-off-by: Luis Alves <ljalvs@gmail.com>
> ---
>  drivers/media/tuners/si2157.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/tuners/si2157.c b/drivers/media/tuners/si2157.c
> index 6c53edb..e2de428 100644
> --- a/drivers/media/tuners/si2157.c
> +++ b/drivers/media/tuners/si2157.c
> @@ -245,6 +245,7 @@ static int si2157_set_params(struct dvb_frontend *fe)
>  			break;
>  	case SYS_DVBC_ANNEX_A:
>  			delivery_system = 0x30;
> +			bandwidth = 0x08;

Hmm... this patch looks wrong, as it will break DVB-C support where
the bandwidth is lower than 6MHz.

The DVB core sets c->bandwidth_hz for DVB-C based on the rolloff and
the symbol rate. If this is not working for you, then something else
is likely wrong.

I suggest you to add a printk() there to show what's the value set
at c->bandwidth_hz and what's the symbol rate that you're using.

On DVB-C, the rolloff is fixed (1.15 for annex A and 1.13 for Annex C).
Not sure if DVB-C2 allows selecting a different rolloff factor, nor
if si2157 works with DVB-C2.

>  			break;
>  	default:
>  			ret = -EINVAL;