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

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Date:	Mon, 14 Sep 2015 18:17:03 +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 06:11 PM, Vaibhav Hiremath wrote:
>
>
> On Monday 14 September 2015 04:04 PM, Ulf Hansson wrote:
>> On 14 September 2015 at 11:42, Vaibhav Hiremath
>> <vaibhav.hiremath@...aro.org> wrote:
>>>
>>>
>>> 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.
>>
>> Pinctrl would work as well, or perhaps a combination of both pinctrl
>> and a regulator.
>
>
> Not sure, how I can propagate "call coming from MMC/SD" to both
> regulator and pinctrl.
> Probably pinctrl would already know, but then it doesn't know the
> voltage settings.
>
> Let me spend some time, but atleast at this point I am not sure.
>
>>

On the side note,
Lets park this patch aside, till I get back with better option.

It would be nice if you could review other patches, let them notget
blocked due to this.


Thanks,
Vaibhav
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