Re: [PATCH] mmc: Prevent 1.8V switch for SD hosts that don't support UHS modes.

[Chris Ball <cjb@laptop.org>]

Hi Al,

On Mon, Apr 02 2012, Alan Cooper wrote:
> Still hoping for comments on the patch.

Thanks for the reminder; adding a few potential reviewers to CC:.

- Chris.

> On Fri, Mar 16, 2012 at 3:54 PM, Al Cooper <acooper@gmail.com> wrote:
>> The driver should not try to switch to 1.8V when the SD 3.0 host
>> controller does not have any UHS capabilities bits set (SDR50, DDR50
>> or SDR104). See page 72 of "SD Specifications Part A2 SD Host
>> Controller Simplified Specification Version 3.00" under
>> "1.8V Signaling Enable". Instead of setting SDR12 and SDR25 in the host
>> capabilities data structure for all V3.0 host controllers, only set them
>> if SDR104, SDR50 or DDR50 is set in the host capabilities register. This
>> will prevent the switch to 1.8V later.
>>
>> Signed-off-by: Al Cooper <acooper@gmail.com>
>> ---
>>  drivers/mmc/host/sdhci.c |    5 +++--
>>  1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 8d66706..cdf900e 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -2762,8 +2762,9 @@ int sdhci_add_host(struct sdhci_host *host)
>>            mmc_card_is_removable(mmc))
>>                mmc->caps |= MMC_CAP_NEEDS_POLL;
>>
>> -       /* UHS-I mode(s) supported by the host controller. */
>> -       if (host->version >= SDHCI_SPEC_300)
>> +       /* Any UHS-I mode in caps implies SDR12 and SDR25 support. */
>> +       if (caps[1] & (SDHCI_SUPPORT_SDR104 | SDHCI_SUPPORT_SDR50 |
>> +                      SDHCI_SUPPORT_DDR50))
>>                mmc->caps |= MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25;
>>
>>        /* SDR104 supports also implies SDR50 support */
>> --
>> 1.7.6

-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child