Re: [PATCH V1] mmc: core: Wait for 1ms after enabling the clocks post voltage switch

[Adrian Hunter]

On 17/11/22 17:23, Adrian Hunter wrote:
> On 17/11/22 13:07, Ulf Hansson wrote:
>> On Thu, 17 Nov 2022 at 10:49, Sarthak Garg <quic_sartgarg@xxxxxxxxxxx> wrote:
>>>
>>> As per spec we should wait for 1ms after providing the SD clock to the
>>> card again as part of voltage switch sequence but there seems to be a
>>> violation here. Clocks are getting gated before 1ms as part of
>>> sdhci_set_ios function where we try to reset SD Clock Enable by
>>> resetting SDHCI_CLOCK_CARD_EN bit in SDHCI_CLOCK_CONTROL register
>>> leading to voltage switch failures for specific SD cards.
>>> Below ftraces also confirms the above understanding :
>>>
>>> 9.511367: mmc_host_set_uhs_voltage: mmc1 called
>>> 9.511369: mmc_set_ios: mmc1: clock 0Hz busmode 2 powermode 2 cs 0
>>> Vdd 18 width 1 timing 0
>>> 9.511370: sdhci_set_ios: mmc1 called
>>> 9.511370: sdhci_set_ios: mmc1 setting clock ios->clock: 0 host->clock:
>>> 400000
>>> 9.511372: sdhci_msm_set_clock: mmc1 clock: 0
>>> 9.511394: sdhci_set_ios: mmc1 gating clocks by writing
>>> ~SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
>>> 9.511413: sdhci_msm_set_clock: mmc1 clock: 0
>>> 9.511423: mmc_set_signal_voltage: mmc1 called
>>> 9.533816: mmc_set_ios: mmc1: clock 400000Hz busmode 2 powermode 2 cs 0
>>> Vdd 18 width 1 timing 0
>>> 9.533820: sdhci_set_ios: mmc1 called
>>> 9.533822: sdhci_set_ios: mmc1 setting clock ios->clock: 400000
>>> host->clock: 0
>>> 9.533826: sdhci_msm_set_clock: mmc1 clock: 400000
>>> 9.533925: sdhci_enable_clk: mmc1 Enabling clocks by writing
>>> SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
>>> 9.533950: sdhci_set_ios: mmc1 gating clocks by writing
>>> ~SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
>>> 9.533973: sdhci_msm_set_clock: mmc1 clock: 400000
>>> 9.534043: sdhci_enable_clk: mmc1 Enabling clocks by writing
>>> SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
>>> 9.534045: mmc_host_set_uhs_voltage: mmc1 Done
>>>
>>> Wait for 1ms after enabling the clock post voltage switch to make sure
>>> clock is kept alive for alteast 1ms as per spec.
>>>
>>> Signed-off-by: Sarthak Garg <quic_sartgarg@xxxxxxxxxxx>
>>
>> I don't know the exact behaviour of sdhci around this, so I will defer
>> to Adrian's input for that.
> 
> sdhci_set_ios() seems to be mucking around with the clock way
> more than necessary.  I'll go over it and see what can be done.

I have now sent some patches:

  https://lore.kernel.org/linux-mmc/20221124170649.63851-1-adrian.hunter@xxxxxxxxx/T/#t

> 
>>
>> However, let me point out that in mmc_set_uhs_voltage() we are trying
>> to take the 1ms into account. More precisely, after
>> mmc_host_set_uhs_voltage() has been called to switch the voltage to
>> 1.8V and to re-enable the clock, mmc_set_uhs_voltage() does a
>> "mmc_delay(1)" and then it calls the ->card_busy() ops to check that
>> card doesn't signal busy by holding DAT0 low.
>>
>> I understand that the code in mmc_set_uhs_voltage(), expects the host
>> to be rather dumb from the HW perspective, which may not always be the
>> case. Although, I would rather avoid introducing new host flags, along
>> what you propose in the $subject patch. If this can't be managed in
>> sdhci, without some new help from the mmc core, I would rather suggest
>> that we introduce a new host callback that can be used to replace the
>> entire part in mmc_host_set_uhs_voltage() (or something along those
>> lines).
>>
>> Kind regards
>> Uffe
>>
>>> ---
>>>  drivers/mmc/core/core.c  | 4 ++++
>>>  drivers/mmc/host/sdhci.c | 3 +++
>>>  include/linux/mmc/host.h | 1 +
>>>  3 files changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index a1efda85c6f2..d63e00aab6cb 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -1181,6 +1181,8 @@ int mmc_host_set_uhs_voltage(struct mmc_host *host)
>>>         host->ios.clock = 0;
>>>         mmc_set_ios(host);
>>>
>>> +       host->doing_signal_voltage_switch = true;
>>> +
>>>         if (mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180))
>>>                 return -EAGAIN;
>>>
>>> @@ -1189,6 +1191,8 @@ int mmc_host_set_uhs_voltage(struct mmc_host *host)
>>>         host->ios.clock = clock;
>>>         mmc_set_ios(host);
>>>
>>> +       host->doing_signal_voltage_switch = false;
>>> +
>>>         return 0;
>>>  }
>>>
>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>> index fb6e9a81f198..ac7c254eef4b 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -2312,6 +2312,9 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>>>                 host->ops->set_clock(host, ios->clock);
>>>                 host->clock = ios->clock;
>>>
>>> +               if (mmc->doing_signal_voltage_switch)
>>> +                       usleep_range(1000, 1250);
>>> +
>>>                 if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK &&
>>>                     host->clock) {
>>>                         host->timeout_clk = mmc->actual_clock ?
>>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
>>> index 8fdd3cf971a3..06c88cd7a8bf 100644
>>> --- a/include/linux/mmc/host.h
>>> +++ b/include/linux/mmc/host.h
>>> @@ -521,6 +521,7 @@ struct mmc_host {
>>>         bool                    hsq_enabled;
>>>
>>>         u32                     err_stats[MMC_ERR_MAX];
>>> +       bool                    doing_signal_voltage_switch;
>>>         unsigned long           private[] ____cacheline_aligned;
>>>  };
>>>
>>> --
>>> 2.17.1
>>>
>