linux-kernel - Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage

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Date:   Mon, 14 Sep 2020 11:08:14 +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 13/21] mmc: sdhci: UHS-II support, skip
 signal_voltage_switch()

On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> Adrian,
> 
> On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
>> On 10/07/20 2:11 pm, Ben Chuang wrote:
>>> From: AKASHI Takahiro <takahiro.akashi@...aro.org>
>>>
>>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
>>> and not for UHS-II mode.
>>>
>>> Signed-off-by: Ben Chuang <ben.chuang@...esyslogic.com.tw>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>>> ---
>>>  drivers/mmc/host/sdhci.c | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>> index 5511649946b9..7f2537648a08 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>>>  	/*
>>>  	 * Signal Voltage Switching is only applicable for Host Controllers
>>>  	 * v3.00 and above.
>>> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
>>> +	 * already 1.8v so no voltage switch required.
>>>  	 */
>>> -	if (host->version < SDHCI_SPEC_300)
>>> +	if (host->version < SDHCI_SPEC_300 ||
>>> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
>>> +	     host->version >= SDHCI_SPEC_400 &&
>>> +	     host->mmc->flags & MMC_UHS2_SUPPORT))
>>
>> Please look at hooking ->start_signal_voltage_switch() instead
> 
> Do you mean that you want every platform driver who wants to support UHS-II
> to set NULL to start_signal_voltage_switch hook even if this hack is
> platform agnostic?

No, I see UHS-II as a separate layer i.e.

 UHS-II host controller driver
  |   |
  |   v
  |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
  |   |
  v   v
  sdhci e.g. sdhci_start_signal_voltage_switch

Most things should go through sdhci-uhs2 but not nessarily everything.