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

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Date:   Wed, 16 Sep 2020 09:42:28 +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 15/09/20 9:24 am, AKASHI Takahiro wrote:
> Adrain,
> 
> On Mon, Sep 14, 2020 at 09:36:02AM +0300, Adrian Hunter wrote:
>> 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,
>>>         ...
>>> }
> 
> What do you think about this logic in general?
> (If necessary, read it replacing "foo" to "uhs2".)
> 
> What I'm concerned about is SDHCI_POWER_CONTROL register.
> Vdd and vdd2 are controlled with corresponding bits in this register.
> It seems to be "natural" to me that vdd and vdd2 are enabled
> in a single function rather than putting them in separate ones.
> 
> In particular, in the case of sdhci_set_power_noreg(), there exist a couple
> of "quirks" around writing the bits to SDHCI_POWER_CONTROL register.

We can treat UHS-II support as being for new hardware and therefore
we don't necessarily need to support old quirks.  Just make sure if
a quirk is not being supported, to add a comment to that effect.

> I don't know how we should handle them if we have a separate function,
> say, sdhci_uhs2_set_power_noreg().
> Do you want to see a copy of the same logic in sdhci_uhs2_set_power_noreg()? 

I would probably consider making another function that non-UHS-II
drivers do not need to care about e.g. existing drivers can keep using
sdhci_set_power_noreg() and sdhci_uhs2 can call __sdhci_set_power_noreg()

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 592a55a34b58..ffe54f06fe38 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2013,8 +2013,8 @@ static void sdhci_set_power_reg(struct sdhci_host *host, unsigned char mode,
 		sdhci_writeb(host, 0, SDHCI_POWER_CONTROL);
 }
 
-void sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
-			   unsigned short vdd)
+void __sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
+			   unsigned short vdd, u8 vdd2)
 {
 	u8 pwr = 0;
 
@@ -2048,7 +2048,7 @@ void sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
 	if (host->pwr == pwr)
 		return;
 
-	host->pwr = pwr;
+	host->pwr = pwr | vdd2;
 
 	if (pwr == 0) {
 		sdhci_writeb(host, 0, SDHCI_POWER_CONTROL);
@@ -2085,6 +2085,13 @@ void sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
 			mdelay(10);
 	}
 }
+EXPORT_SYMBOL_GPL(__sdhci_set_power_noreg);
+
+void sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
+			   unsigned short vdd)
+{
+	__sdhci_set_power_noreg(host, mode, vdd, 0);
+}
 EXPORT_SYMBOL_GPL(sdhci_set_power_noreg);
 
 void sdhci_set_power(struct sdhci_host *host, unsigned char mode,

> 
> -Takahiro Akashi
> 
> 
>>>
>>> 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