linux-kernel - Re: [PATCH 1/2] mmc: sdhci: Added set_power sdhci

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Message-ID: <Pine.LNX.4.64.1305230920430.23354@axis700.grange>
Date:	Thu, 23 May 2013 09:25:16 +0200 (CEST)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Felipe Ferreri Tonello <eu@...ipetonello.com>
cc:	linux-mmc@...r.kernel.org, ben-linux@...ff.org, cjb@...top.org,
	arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mmc: sdhci: Added set_power sdhci_ops handler.

On Wed, 22 May 2013, Felipe Ferreri Tonello wrote:

> Hi Guennadi,
> 
> On Wednesday, May 22, 2013 10:30:40 PM Guennadi Liakhovetski wrote:
> > On Wed, 22 May 2013, Felipe F. Tonello wrote:
> > > From: "Felipe F. Tonello" <eu@...ipetonello.com>
> > > 
> > > This is useful for power managment purposes if a sdhci child host wants to
> > > turn off some other peripheral also.
> > 
> > Sorry, could you elaborate a bit? In what situations is it exactly useful?
> > And why cannot the regulator API be used there?
> 
> Sorry about that.
> 
> One example that I can think of is when you have a wifi module connected as a 
> mmc card via sdio. So you can register a callback function in your machine 
> source code to turn on/off the wifi module based on the mmc host power.

Ok, understand. Your second patch in this series adds such a callback in 
your SDHCI host driver and there it just calls a platform callback. I 
don't think this is a good idea. First, we want to go away from platform 
callbacks, because they are incompatible with DT. Second, because the 
proper solution IMHO would be for your platform to export a regulator, and 
the SDHCI core driver already includes regulator support.

> I've seen this implementation in others mmc hosts, such as omap.

Which, however, doesn't yet mean, it's a good idea :)

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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