linux-kernel - Re: [PATCH 03/19 v2] Staging: xgifb: Remove LCDA detection in xgifb

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Message-ID: <20120709220801.GA19103@blackmetal.musicnaut.iki.fi>
Date:	Tue, 10 Jul 2012 01:08:01 +0300
From:	Aaro Koskinen <aaro.koskinen@....fi>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Miguel Gómez <magomez@...lia.com>,
	arnaud.patard@...-net.org, dan.carpenter@...cle.com,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/19 v2] Staging: xgifb: Remove LCDA detection in
 xgifb_probe().

Hi,

On Mon, Jul 09, 2012 at 11:39:47AM -0700, Greg KH wrote:
> On Fri, Jul 06, 2012 at 12:40:38PM +0200, Miguel Gómez wrote:
> > The piece of code that checks for LCDA in xgifb_probe() just checks for some
> > register values but doesn't really do anything in response to them (the actions
> > that should be executed are commented).
> > As nothing is really being done, the code can be safely removed.
> 
> Are you sure?  Some devices (foolish ones that is) need registers read
> to work properly as that is part of their start-up logic.  Yeah, it
> doesn't seem to make sense, but hardware designers usually have good
> reasons for doing this type of thing.  Or at least they think they do :)

Those registers (CR 0x30..0x38) are scratch registers, so reading them
should have no side effects in the device side. I think it's safe to
delete that code.

A.
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