linux-kernel - Re: [RFC 1/3] saa7115: Set saa7113 init to values from datasheet

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Date:	Fri, 31 May 2013 17:08:02 +0300
From:	Timo Teras <timo.teras@....fi>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Jon Arne Jørgensen <jonarne@...arne.no>,
	Andy Walls <awalls@...metrocast.net>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	hans.verkuil@...co.com, prabhakar.csengg@...il.com,
	g.liakhovetski@....de, ezequiel.garcia@...e-electrons.com
Subject: Re: [RFC 1/3] saa7115: Set saa7113 init to values from datasheet

On Fri, 31 May 2013 10:08:27 -0300
Mauro Carvalho Chehab <mchehab@...hat.com> wrote:

> Em Thu, 30 May 2013 21:00:01 +0200
> Jon Arne Jørgensen <jonarne@...arne.no> escreveu:
> 
> > On Thu, May 30, 2013 at 08:33:32AM +0300, Timo Teras wrote:
> > > I would rather have the platform_data provide the new table. Or
> > > if you think bulk of the table will be the same for most users,
> > > then perhaps add there an enum saying which table to use - and
> > > name the tables according to the chip variant it applies to.
> > > 
> > 
> > I think the bulk of the table will be the same for all drivers.
> > It's one bit here and one bit there that needs changing.
> > As the driver didn't support platform data.
> > Changing to a new init table for the drivers that implement
> > platform_data shouldn't cause any regressions.
> 
> There are several things that are very bad on passing a table via
> platform data:

Sorry, my wording was self-conflicting. The intention was to
suggest providing an enum saying which table to use. Not that the
platform data would provide the whole table.

> 	1) you're adding saa711x-specific data at the bridge driver,
> 	   so, the saa711x code is spread on several places at the
> 	   long term;
> 
> 	2) some part of the saa711x code may override the data there, 
> 	   as it is not aware about what bits should be preserved from
> 	   the new device;
> 
> 	3) due (2), latter changes on the code are more likely to
> 	   cause regressions;
> 
> 	4) also due to (2), some hacks can be needed, in order to warn
> 	   saa711x to handle some things differently.

Agreed.

> That's why it is a way better to add meaningful parameters telling
> what bits are needed for the driver to work with the bridge. That's
> also why we do this with all other drivers.

Based on the latest patch, more of these bits need to be controlled
individually than I figured. So yes, individual meaningful bits do make
the most sense.

Thanks,
 Timo
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