Re: [PATCH v4 1/3] mmc: dw_mmc: update clock after host reach a stable voltage

[Doug Anderson]

Alim and Addy,

On Sun, Feb 15, 2015 at 3:28 PM, Alim Akhtar <alim.akhtar@xxxxxxxxx> wrote:
> Hi Addy,
>
> On Sat, Feb 14, 2015 at 11:47 AM, Addy Ke <addy.ke@xxxxxxxxxxxxxx> wrote:
>> As show in mmc_power_up(), in MMC_POWER_UP state, the voltage isn't
>> stable and we may get 'data busy' which can't be cleaned by resetting
>> all blocks. So we should not send command to update clock in this state.
>>
>> Signed-off-by: Addy Ke <addy.ke@xxxxxxxxxxxxxx>
>> ---
>>  drivers/mmc/host/dw_mmc.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index 4d2e3c2..3472f9b 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -1102,7 +1102,8 @@ static void dw_mci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>>                 drv_data->set_ios(slot->host, ios);
>>
>>         /* Slot specific timing and width adjustment */
>> -       dw_mci_setup_bus(slot, false);
>> +       if (ios->power_mode != MMC_POWER_UP)
>> +               dw_mci_setup_bus(slot, false);
>>
> This looks a HACK to me.
> If stabilizing host voltage regulator is the problem, can you try out
> below patch, and see if this resolve your issue?

Actually, IMHO Alim's patch is more of a hack than Addy's.  There's
already a 10ms delay between "power up" and "power on" in the MMC core
in mmc_power_up() state.  That delay is commented as:

  /*
   * This delay should be sufficient to allow the power supply
   * to reach the minimum voltage.
   */
  mmc_delay(10);

That means that assuming that the voltage is stable in MMC_POWER_UP is
not valid anyway.


Addy's patch certainly needs more comments.  In another context Olof suggested:

/*
 * Skip bus setup while voltage is still stabilizing. Instead,
 * bus setup will be done at MMC_POWER_ON.
 */


...thinking about this more, though: really the voltage should be
stabilized when the regulator call returns (see my comments below).
In actuality the "right" fix might be to just rearrange this function
a little not to turn the clock on _before_ we even try to turn the
voltage on.

I've got that coded up but I'm still testing it...  If you want to try
it too, you can find it at
<https://chromium-review.googlesource.com/251341>.

Note that without my patch I find that I _really_ need Addy's patch to
make sure that the card isn't busy in setup_bus.  With my patch Addy's
code catches the card busy less often.  I'm still trying to see if
there's a way to totally remove the need for his setup_bus and still
trying to grok all the patches flying around...


> ===========
> [PATCH] mmc: dw_mmc: Wait for host voltage regulator to be stable
>
> Signed-off-by: Alim Akhtar <alim.akhtar@xxxxxxxxxxx>
> ---
>  drivers/mmc/host/dw_mmc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 4d2e3c2..dc10fbb 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1202,6 +1202,9 @@ static int dw_mci_switch_voltage(struct mmc_host
> *mmc, struct mmc_ios *ios)
>   }
>   mci_writel(host, UHS_REG, uhs);
>
> + /* wait for 5ms so that host voltage regulator is stable */
> + usleep_range(5000, 5500);
> +

Alim: if you have some other instance where you actually need VQMMC to
stabilize it should probably be done in a different way.  If I
understand correctly it is the regulator core's job to make sure that
voltage is stable before returning.  If you have a gpio-regulator you
may be able to use "startup-delay-us" to specify how long the
regulator takes to come up.  You could also look at
'regulator-enable-ramp-delay'

-Doug
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