linux-kernel - Re: [RFC 2/3] mmc: sdhci: add host_ops->voltage

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Date:	Mon, 14 Sep 2015 15:12:53 +0530
From:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Jisheng Zhang <jszhang@...vell.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 2/3] mmc: sdhci: add host_ops->voltage_switch callback for
 all other voltages



On Monday 14 September 2015 03:00 PM, Ulf Hansson wrote:
> [...]
>
>>>>>
>>>>> Could this be implemented by regulator API? From patch set 3/3, the
>>>>> pxa1928
>>>>> voltage_switch hook is to operate the IO pad registers, this seems not
>>>>> belong
>>>>> to the SDHC IP core.
>>>>>
>>>>
>>>> Not quite sure whether regulator would be right fit for this.
>>>
>>>
>>>   From the patche[3/3], this can be achieved by abstracting the IO PAD as
>>> regulators
>>> then, we may not need to touch the core sdhci.c. But I'm not sure whether
>>> this
>>> is the good solution or not.
>>
>>
>> Exactly...
>>
>>> sdhci Maintainers and experts may have better
>>> suggestions.
>>>
>>
>> Thats is the reason I stamped it as a RFC :)
>>
>
> [...]
>
>  From an mmc core perspective it would be preferred if you implement
> this as a regulator (vqmmc).
>
> Especially since we will soon have an API for how to set the I/O
> voltages - and the intelligence within that API is not something we
> would like to implement for each and every host driver.
> https://lkml.org/lkml/2015/8/31/367
>


I would still consider this as a regulator specific and may not address
the IO configuration within the SoC which are module specific.
The API regulator_set_voltage_triplet() will not have intelligence to
differentiate whether the call is coming from MMC or somewhere else.

Note that, the IO pad voltage configuration which I am referring to is
MMC specific and applicable only when pad is configured in MMC mode. So
technically it is not simply common pad voltage configuration.


And I am still not sure regulator framework would be right fit for
this. Pinctrl would have been right fit, but...since I saw f_sdh30
driver is already doing this, which is easy fit; so adopted the same.

Thanks,
Vaibhav
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