linux-kernel - Re: mfd: Core driver for Winbond chips

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Message-ID: <20130409161838.GB27050@roeck-us.net>
Date:	Tue, 9 Apr 2013 09:18:38 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Wim Van Sebroeck <wim@...ana.be>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
	Pádraig Brady <P@...igBrady.com>
Subject: Re: mfd: Core driver for Winbond chips

On Tue, Apr 09, 2013 at 01:45:44PM +0200, Wim Van Sebroeck wrote:
> Hi Guenter,
> 
> > I was waiting for feedback from Wim, who submitted a similar driver, about his
> > thoughts. Key question is how to reserve access to the shared resource - either
> > through an exported function in the mfd driver requesting a mutex, or through
> > request_muxed_region(). I am going back and forth myself on which one is better.
> > 
> > Maybe it does not really matter, but using a function has the slight advantage
> > that it auto-loads and locks the mfd module while one of its client modules
> > is loaded. If we use request_muxed_region, that is not the case and the client
> > module must use another means to request and lock the mfd module.
> > 
> > Maybe you have an opinion ?
> 
> This is indeed the main issue that has to be solved. Both options will work.
> I like the auto-load and lock, but I need to look at the request_muxed_region
> code again first before I can see what the possible drawbacks are :-).
> 
One drawback of using request_muxed_region is that it needs a return value
from superio_enter. Also, it needs some code in the client driver init function
to ensure that the mfd driver gets loaded, and possibly a call to __module_get()
in the client driver probe function to keep the mfd driver loaded.

winbond_superio_enter() would not need a return value and could use
devm_request_region. We could also consider allocating the hwmon memory space in
the mfd driver and pass it as resource to the client drivers, which would remove
a few more lines of code from those.

Overall I am slightly in favor of using an exported function.

Guenter
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