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

[Alim Akhtar]

Hi Doug,


On Fri, Feb 20, 2015 at 5:19 AM, Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
> 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:
>
Well, my suggestion (adding 5ms in switch_volatge) was based on DW_MMC
databook (V2.41a) section "7.4.1.2 Voltage switch Normal Scenario"
step #7 which says:" After the 5ms timer expires, the host voltage
regulator is stable".

PS: I have limited to no access of my mails and workstation until
March 9th, so replies will be slow.

>   /*
>    * 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



-- 
Regards,
Alim
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