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

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Date:	Fri, 24 May 2013 13:02:58 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Felipe Ferreri Tonello <eu@...ipetonello.com>,
	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 05/23/2013 04:25 PM, Guennadi Liakhovetski wrote:
> 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.
We can use the regulator framework.
i think this callback function didn't need.

Best Regards,
Jaehoon Chung
> 
>> 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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