2012/9/26 Girish K S <girish.shivananjappa@xxxxxxxxxx>:
> On 26 September 2012 20:38, Kevin Liu <keyuan.liu@xxxxxxxxx> wrote:
>> From: Kevin Liu <kliu5@xxxxxxxxxxx>
>>
>> Host controller must enable 1.8v signal for UHS modes.
>> Otherwise UHS modes won't take effect.
>> But mmc core does NOT switch to 1.8v for DDR50 mode.
>> So enable the 1.8v signal for mmc DDR50 mode in host
>> driver.
>>
>> Signed-off-by: Kevin Liu <kliu5@xxxxxxxxxxx>
>> ---
>> drivers/mmc/host/sdhci.c | 9 ++++++++-
>> 1 files changed, 8 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 50e7a54..e3de041 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -1529,8 +1529,15 @@ static void sdhci_do_set_ios(struct sdhci_host *host, struct mmc_ios *ios)
>> ctrl_2 |= SDHCI_CTRL_UHS_SDR50;
>> else if (ios->timing == MMC_TIMING_UHS_SDR104)
>> ctrl_2 |= SDHCI_CTRL_UHS_SDR104;
>> - else if (ios->timing == MMC_TIMING_UHS_DDR50)
>> + else if (ios->timing == MMC_TIMING_UHS_DDR50) {
>> + struct mmc_card *card;
>> +
>> ctrl_2 |= SDHCI_CTRL_UHS_DDR50;
>> + card = container_of(&(host->mmc),
>> + struct mmc_card, host);
>> + if (mmc_card_mmc(card))
>> + ctrl_2 |= SDHCI_CTRL_VDD_180;
>> + }
> If you want to set the voltage to 1.8. It has to be done from the core
> layer using the api mmc_set_signal_voltage during the mmc card init.
> as it is done for 1.2 volts switch. In the comment (mmc_card_init
> function) it is explicitly mentioned
> * 1.8V vccq at 3.3V core voltage (vcc) is not required
> * in the JEDEC spec for DDR.
> can you please check it. Still if you feel its necessary to change the
> voltage to 1.8 v, you can do it from mmc_init_card function
In JEDEC spec, there are two emmc device types which support DDR50.
One type can work under signal 1.2v while the other type work under
signal 1.8v or 3v. So current code just keep 3v for the second device
type.
But in SD host spec, 1.8v signal must be enabled for all UHS modes
taking effect.
So the fact is, if we use SD host to work with emmc chip, we have to
select 1.8v in order to enable DDR50. Current code missed this.
Because DDR50 shall can work under both signal 1.8v and 3v according
to JEDEC spec, So I don't want to switch to 1.8v in mmc core code.
It's the host controller requirement that 1.8v signal must be enabled
in order to enable DDR50, which conflict with emmc spec. So I added
this in host driver.
Thanks
Kevin
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