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

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Date:	Mon, 14 Sep 2015 18:11:36 +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 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.

>
> What I don't like is the solution you have suggested in patch3.
>

As I said, that was easy fit into existing implementation. :)
f_sdh30 already does something similar.

Thanks,
Vaibhav
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