On 15 December 2011 16:22, Girish K S <[email protected]> wrote:
> On 15 December 2011 15:34, Saugata Das <[email protected]> wrote:
>> On 15 December 2011 09:28, Girish K S <[email protected]>
>> 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 <[email protected]>
>>> Signed-off-by: Girish K S <[email protected]>
>>> ---
>>> 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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