linux-kernel - Re: Questions regarding mfd drivers

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Message-Id: <20080205122127.63846543.Kristoffer.ericson@gmail.com>
Date:	Tue, 5 Feb 2008 12:21:27 +0100
From:	Kristoffer Ericson <kristoffer.ericson@...il.com>
To:	Ben Dooks <ben@...ff.org>
Cc:	Kristoffer Ericson <kristoffer.ericson@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Questions regarding mfd drivers

On Mon, 4 Feb 2008 23:01:55 +0000
Ben Dooks <ben@...ff.org> wrote:

> On Mon, Feb 04, 2008 at 12:37:14PM +0100, Kristoffer Ericson wrote:
> > Greetings,
> > 
> > Trying to wrap my head around sm501. From what I can tell an mfd driver is a "master" driver that takes control of all
> > memory and io areas. It then hands out areas of those to drivers. Anywhere near correct?
> 
> Yes, it is the central management for these, but also ensures that any
> of the sub-drivers have properly locked access to the clocks, gpio and
> other shared resources.

Oki

> 
> The mfd driver for the sm501 exports a number of functions for the
> sub drivers to use, you should be able to see what is exported easily
> by the fact they are exported with EXPORT_SYMBOL_GPL(). The header
> files should document basic functionality of this.
> 

Will take a look at that.
 
> > I can see some benefit but still hard for me to motivate. What am I missing? What will the mfd be able to do, that I lack now?
> > 
> > The sm501 driver seems way more advanced than I will need for hd64461/hd64465 anyhow, but still need to understand sm501 completely before
> > attempting to write one on my own. Anyone know any documentation aside from example drivers?
> 
> Are you trying to write your own SM501, or something else? It seems
> you are writing for something else.
>

Im trying to move the companion chip hd64461 to a more sensible location. Paul suggested building an mfd driver.
The hd64461 chipset supplies for example pcmcia and framebuffer support. Its not as advanced as the SM501.
 
> If the chip you are targetting has shared resources, such as clock
> gates, PLLs, or gpio that other drivers need to touch, then the best
> way to go is for an mfd driver to provide this functionality and have
> all the child drivers use the exported functionality.

Oki, sounds good. Thanks for info.

> 
> -- 
> Ben (ben@...ff.org, http://www.fluff.org/)
> 
>   'a smiley only costs 4 bytes'
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