Aw: Re: [PATCH 2/3] media: si2157: add support for 1.7MHz and 6.1 MHz

[Robert Schlabbach <robert_s@gmx.net>]

"Mauro Carvalho Chehab" <mchehab@kernel.org> wrote:

> As the DVB core already stores the bandwidth used to tune at props,
> since the introduction of DVBv5 API, any get calls will return the
> tuned bandwidth.

No, not the _tuned_ bandwidth, the "requested" bandwidth, that was
estimated. I see no value in that information, as the user app can
easily calculate that by itself. This is not information that the
kernel or driver needs to provide, as it is solely derived from
the information the application has given.

Whereas the _actually applied_ bandwidth filter is an information
that only the tuner driver can deliver. For example, there are 5MHz
DVB-T2 channels, but the si2157 only offers a 6MHz bandwidth filter.

What should get_frontend() return, the requested/nominal 5MHz, or
the actually used 6MHz?

Reading the include file, the answer seems clear to me:

https://git.linuxtv.org/media_tree.git/tree/include/media/dvb_frontend.h

> * @get_frontend:	callback function used to inform the parameters
> *			actuall in use.

So following that documentation, I would say the actually used 6MHz
should be put into the property cache by that callback.

> Thanks, patches look sane on my eyes.

Thanks for your quick review.

Best Regards,
-Robert Schlabbach