On 14 August 2014 11:54, Chuanxiao Dong <chuanxiao.d...@intel.com> wrote:
> Even (e)MMC card can support 3.3v to 1.2v vccq in DDR, but not all
> host controller can support this, like some of the SDHCI host
> which connect to an eMMC device. Some of these host controller
> still needs to use 1.8v vccq for supporting DDR mode.
>
> So the sequence will be:
> if (host and device can both support 1.2v IO)
> use 1.2v IO;
> else if (host and device can both support 1.8v IO)
> use 1.8v IO;
> so if host and device can only support 3.3v IO, this is the last choice.
>
> Signed-off-by: Chuanxiao Dong <chuanxiao.d...@intel.com>
> Signed-off-by: Yunpeng Gao <yunpeng....@intel.com>
> ---
> Changelog V2:
> - For (e)MMC device switching to DDR mode, try 1.2v singaling first. Then
> try 1.8v. If 1.2v and 1.8v are both not supported, use the default 3.3v
>
> drivers/mmc/core/mmc.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 793c6f7..aa5180b 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -988,8 +988,19 @@ static int mmc_select_hs_ddr(struct mmc_card *card)
> * 1.8V vccq at 3.3V core voltage (vcc) is not required
> * in the JEDEC spec for DDR.
> *
> - * Do not force change in vccq since we are obviously
> - * working and no change to vccq is needed.
> + * Even (e)MMC card can support 3.3v to 1.2v vccq, but not all
> + * host controller can support this, like some of the SDHCI
> + * controller which connect to an eMMC device. Some of these
> + * host controller still needs to use 1.8v vccq for supporting
> + * DDR mode.
> + *
> + * So the sequence will be:
> + * if (host and device can both support 1.2v IO)
> + * use 1.2v IO;
> + * else if (host and device can both support 1.8v IO)
> + * use 1.8v IO;
> + * so if host and device can only support 3.3v IO, this is the
> + * last choice.
> *
> * WARNING: eMMC rules are NOT the same as SD DDR
> */
> @@ -998,6 +1009,11 @@ static int mmc_select_hs_ddr(struct mmc_card *card)
> MMC_SIGNAL_VOLTAGE_120);
> if (err)
> return err;
> + } else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_DDR_1_8V) {
If we encounter errors switching to 1.2V, it would be nice to fall
back and to test with 1.8V.
You may get influenced by the code in mmc_select_hs200(), where a
similar approach is taken.
> + err = __mmc_set_signal_voltage(host,
> + MMC_SIGNAL_VOLTAGE_180);
> + if (err)
> + return err;
> }
>
> mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
> --
> 1.7.10.4
>
Kind regards
Uffe
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