linux-kernel - Re: [RFC PATCH V3 15/21] mmc: sdhci: UHS-II support, modify set

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Date:   Mon, 14 Sep 2020 09:36:02 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Ben Chuang <benchuanggli@...il.com>, ulf.hansson@...aro.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        ben.chuang@...esyslogic.com.tw, greg.tu@...esyslogic.com.tw
Subject: Re: [RFC PATCH V3 15/21] mmc: sdhci: UHS-II support, modify
 set_power() to handle vdd2

On 14/09/20 8:45 am, AKASHI Takahiro wrote:
> Adrian,
> 
> On Fri, Aug 21, 2020 at 05:11:18PM +0300, Adrian Hunter wrote:
>> On 10/07/20 2:11 pm, Ben Chuang wrote:
>>> From: AKASHI Takahiro <takahiro.akashi@...aro.org>
>>>
>>> VDD2 is used for powering UHS-II interface.
>>> Modify sdhci_set_power_and_bus_voltage(), sdhci_set_power_noreg()
>>> and sdhci_set_power_noreg() to handle VDD2.
>>
>> vdd2 is always 1.8 V and I suspect there may never be support for anything
>> else, so we should start with 1.8 V only.
> 
> What do you mean here?
> You don't want to add an extra argument, vdd2, to sdhci_set_power().
> Correct?

Yes

> 
>> Also can we create uhs2_set_power_reg() and uhs2_set_power_noreg() and use
>> the existing ->set_power() callback
> 
> Again what do you expect here?
> 
> Do you want to see any platform-specific mmc driver who supports UHS-II
> to implement its own call back like:

Not exactly.  I expect there to be a common implementation in sdhci-uhs2.c
called sdhci_uhs2_set_power() for example, that drivers can use by setting
their .set_power = sdhci_uhs2_set_power.  If they need platform-specific
code as well then their platform-specific code can call
sdhci_uhs2_set_power() if desired.

> 
> void sdhci_foo_set_power(struct sdhci_host *host, unsigned char mode,
>                                   unsigned short vdd)
> {
>         sdhci_set_power(host, mode,vdd);
> 
>         /* in case that sdhci_uhs2 module is not inserted */
>         if (!(mmc->caps & MMC_CAP_UHS2))
>                 return;
> 
>         /* vdd2 specific operation */
>         if (IS_ERR_OR_NULL(host->mmc->supply.vmmc2))
>                 sdhci_uhs2_set_power_noreg(host, mode);
>         else
>                 sdhci_uhs2_set_power_reg(host, mode);
> 
>         /* maybe more platform-specific initialization */
> }
> 
> struct sdhci_ops sdhci_foo_ops = {
>         .set_power = sdhci_foo_set_power,
>         ...
> }
> 
> Is this what you mean?
> (I'm not quite sure yet that sdhci_ush2_set_power_noreg() can be split off
> from sdhci_set_power_noreg().)
> 
> -Takahiro Akashi