Re: [PATCH V2] mmc: core: Add host capability check for power class

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On 15 December 2011 16:22, Girish K S <girish.shivananjappa@xxxxxxxxxx> wrote:
> On 15 December 2011 15:34, Saugata Das <saugata.das@xxxxxxxxxx> wrote:
>> On 15 December 2011 09:28, Girish K S <girish.shivananjappa@xxxxxxxxxx> wrote:
>>> This patch adds a check whether the host supports maximum current value
>>> obtained from the device's extended csd register for a selected interface
>>> voltage and frequency.
>>>
>>> cc: Chris Ball <cjb@xxxxxxxxxx>
>>> Signed-off-by: Girish K S <girish.shivananjappa@xxxxxxxxxx>
>>> ---
>>> Changes in v2:
>>>        deleted a unnecessary if else condition identified by subhash J
>>> Changes in v1:
>>>       reduced the number of comparisons as per Hein's suggestion
>>>
>>>  drivers/mmc/core/mmc.c   |   19 +++++++++++++++++++
>>>  include/linux/mmc/card.h |    4 ++++
>>>  2 files changed, 23 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>> index 006e932..b9ef777 100644
>>> --- a/drivers/mmc/core/mmc.c
>>> +++ b/drivers/mmc/core/mmc.c
>>> @@ -688,6 +688,25 @@ static int mmc_select_powerclass(struct mmc_card *card,
>>>                pwrclass_val = (pwrclass_val & EXT_CSD_PWR_CL_4BIT_MASK) >>
>>>                                EXT_CSD_PWR_CL_4BIT_SHIFT;
>>>
>>> +       if (pwrclass_val >= MMC_MAX_CURRENT_800)
>>> +               pwrclass_val = MMC_MAX_CURRENT_800;
>>> +       else if (pwrclass_val >= MMC_MAX_CURRENT_600)
>>> +               pwrclass_val = MMC_MAX_CURRENT_600;
>>> +       else if (pwrclass_val >= MMC_MAX_CURRENT_400)
>>> +               pwrclass_val = MMC_MAX_CURRENT_400;
>>> +       else
>>> +               pwrclass_val = MMC_MAX_CURRENT_200;
>>> +
>>> +       if ((pwrclass_val == MMC_MAX_CURRENT_800) &&
>>> +           !(card->host->caps & MMC_CAP_MAX_CURRENT_800))
>>> +               pwrclass_val = MMC_MAX_CURRENT_600;
>>> +       if ((pwrclass_val == MMC_MAX_CURRENT_600) &&
>>> +           !(card->host->caps & MMC_CAP_MAX_CURRENT_600))
>>> +               pwrclass_val = MMC_MAX_CURRENT_400;
>>> +       if ((pwrclass_val == MMC_MAX_CURRENT_400) &&
>>> +           !(card->host->caps & MMC_CAP_MAX_CURRENT_400))
>>> +               pwrclass_val = MMC_MAX_CURRENT_200;
>>> +
>>>        /* If the power class is different from the default value */
>>>        if (pwrclass_val > 0) {
>>>                err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>>
>> It is not allowed to set the POWER_CLASS with any value other than
>> what is mentioned in the PWR_CL_ff_vvv or PWR_CL_DDR_ff_vvv  for the
>> corresponding frequency, voltage. That is, if PWR_CL_200_195 is 14 and
>> we want to operate at HS200 then the only value allowed for
>> POWER_CLASS is 14. So, we need to check the PWR_CL numbers and choose
>> the operating mode (HS200/DDR50/..) based on the platform capability
>> to support the current consumption and set the corresponding
>> POWER_CLASS value.
>>
>> Please refer to section 6.6.5 of the 4.5 spec.
>
> The upstreamed code reads the extended csd value based on the already
> set voltage level and frequency of host. So it will get the required
> power class value which can be set directly. Is my understanding
> correct?
>

It is not enough to just check the voltage level and frequency.
Consider this example, host has capability to support
MMC_CAP_MAX_CURRENT_400, the PWR_CL_DDR_52_360 has the value 9 (400mA)
and PWR_CL_200_360 has the value 14 (800mA). Then even though the host
might be capable to run 200MHz clock and 3.6V, it can only enable DDR
at 52MHz and set 9 in POWER_CLASS.

I think, in mmc_select_powerclass, we need to loop through the power
classes of all supported modes of transfer (HS200, DDR52, ... ) and
choose the mode which gives maximum bandwidth but falls within host
capability of current consumption. Then set this to POWER_CLASS byte
and also use the same information when setting HS_TIMING in
mmc_init_card.

>>
>>
>>> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
>>> index 9478a6b..c5e031a 100644
>>> --- a/include/linux/mmc/card.h
>>> +++ b/include/linux/mmc/card.h
>>> @@ -195,6 +195,10 @@ struct mmc_part {
>>>  #define MMC_BLK_DATA_AREA_GP   (1<<2)
>>>  };
>>>
>>> +#define MMC_MAX_CURRENT_200    (0)
>>> +#define MMC_MAX_CURRENT_400    (7)
>>> +#define MMC_MAX_CURRENT_600    (11)
>>> +#define MMC_MAX_CURRENT_800    (13)
>>>  /*
>>>  * MMC device
>>>  */
>>> --
>>> 1.7.1
>>>
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