linux-kernel - Re: [PATCH v4] mmc: mxs-mmc: Introduce regulator support

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Date:   Thu, 31 Jan 2019 14:15:32 +0100
From:   Martin Kepplinger <martin.kepplinger@...zinger.com>
To:     Robin van der Gracht <robin@...tonic.nl>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     Martin Kepplinger <martink@...teo.de>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mmc: mxs-mmc: Introduce regulator support

On 31.01.19 14:09, Robin van der Gracht wrote:
> On Thu, 31 Jan 2019 13:17:23 +0100
> Ulf Hansson <ulf.hansson@...aro.org> wrote:
> 
>> On Thu, 31 Jan 2019 at 09:20, Robin van der Gracht <robin@...tonic.nl> wrote:
>>>
>>> On Mon, 28 Jan 2019 22:15:23 +0100
>>> Ulf Hansson <ulf.hansson@...aro.org> wrote:

...

>>>>
>>>> BTW, you didn't really answer my earlier question about the TI WiFi
>>>> chip. Doesn't you need a special clock for WiFi chip as well? How do
>>>> you intend to manage that?
>>>
>>> I used an external 32K oscillator (SLOW_CLK) for my wl1271. Other
>>> clocks ware generated on the module.
>>
>> Right. How do you control that clock? Did you model it as clock via
>> the common clock framework?
> 
> No I didn't. The slow clock (sleep clock) was always 'on'.
> 
>>
>>>
>>> I had to supply a 'vmmc-supply' in your wl1271 devicetree node,
>>> which will be used to power on/off the wlan module. The supply should
>>> be a (delayed) GPIO controlled 'fixed-regulator' attached to the
>>> wlan_en pin on the module.
>>
>> Right, thanks for explaining.
>>
>>>
>>> 1: Documentation/devicetree/bindings/net/wireless/ti,wlcore.txt
>>>   
>>
>> This sounds like a good fit for mmc pwrseq simple. There are already
>> similar users for it.
>>
>> Have a look at: /drivers/mmc/core/pwrseq*
>> If the mmc host driver calls mmc_of_parse() during ->probe(), a pwrseq
>> instance will be hooked up to it. Once the mmc core tries to power up
>> the card it will make use of the attached pwrseq for the mmc host in
>> question.
>>
>> In this way, you can control the clock and GPIO line, in more exact
>> ways that is needed by the WiFi chip.
> 
> Ack. Makes more sense than using a regulator (even without specifying
> 'clocks').
> 

Thanks Ulf! Sounds promising.

>>
>> Here is a DT example (look for "mmc-pwrseq-simple"):
>> arch/arm/boot/dts/imx6qdl-sr-som-ti.dtsi
>>
>> This should do the trick for you. On the other hand, I don't mind that
>> you still add regulator support to the driver, along the lines of what
>> $subject patch does, however it may not be exactly what you need for
>> the WiFi case.
> 
> @Martin; What do you think? Will you work this out with Ulf?
> Since I can't test this.

I'll test Ulf's suggestion and go that way if I get it to work. Give me 
a few days though.

Thanks a lot for your help so far Robin,

                                martin

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