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

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Date:	Wed, 2 Sep 2015 17:13:57 +0530
From:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	linux-mmc@...r.kernel.org, ulf.hansson@...aro.org,
	linus.walleij@...aro.org, linux-kernel@...r.kernel.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 Wednesday 02 September 2015 01:56 PM, Jisheng Zhang wrote:
> On Wed, 2 Sep 2015 13:49:53 +0530
> Vaibhav Hiremath <vaibhav.hiremath@...aro.org> wrote:
>
>>
>>
>> On Wednesday 02 September 2015 12:34 PM, Jisheng Zhang wrote:
>>> On Wed, 2 Sep 2015 01:02:17 +0530
>>> Vaibhav Hiremath <vaibhav.hiremath@...aro.org> wrote:
>>>
>>>> Currently, the sdhci_do_start_signal_voltage_switch() function invokes
>>>> controller specific voltage switch configuration only for 1.8v usecase;
>>>> but it is required for others as well.
>>>>
>>>> For example, in case of PXA1928 SDH controller, we need to set different
>>>> configuration for 3.3, 1.8 and 1.2 volt support (I/O domain power
>>>> control register).
>>>>
>>>> Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
>>>> ---
>>>> Note:
>>>> Currently ->voltage_switch() callback is only supported
>>>> in f_sdh30 driver. And I am not sure on the dependency of execution
>>>> sequence for that device. I could have moved ->voltage_switch() call
>>>> at one common place (above/below), but was not quite sure about it.
>>>> So, replicated/duplicated the call for other voltages.
>>>>
>>>>    drivers/mmc/host/sdhci.c | 8 ++++++++
>>>>    1 file changed, 8 insertions(+)
>>>>
>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>>> index 3dd295f..b59b76d 100644
>>>> --- a/drivers/mmc/host/sdhci.c
>>>> +++ b/drivers/mmc/host/sdhci.c
>>>> @@ -1753,6 +1753,10 @@ static int sdhci_do_start_signal_voltage_switch(struct sdhci_host *host,
>>>>    		/* Wait for 5ms */
>>>>    		usleep_range(5000, 5500);
>>>>
>>>> +		/* Some controller need to do more when switching */
>>>> +		if (host->ops->voltage_switch)
>>>> +			host->ops->voltage_switch(host, MMC_SIGNAL_VOLTAGE_330);
>>>
>>> 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 :)

Thanks,
Vaibhav
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