> -----Original Message----- > From: linux-mmc-owner@xxxxxxxxxxxxxxx > [mailto:linux-mmc-owner@xxxxxxxxxxxxxxx] On Behalf Of Ulf Hansson > Sent: Tuesday, August 12, 2014 9:21 PM > To: Dong, Chuanxiao > Cc: linux-mmc; chris@xxxxxxxxxx; Gao, Yunpeng > Subject: Re: [PATCH] mmc: core: use 1.8v signling in ddr mode for some special > host > > On 1 August 2014 08:08, Chuanxiao Dong <chuanxiao.dong@xxxxxxxxx> wrote: > > Even eMMC 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. > > > > If a host controller cannot support 3.3v for DDR, try 1.8v. > > > > Signed-off-by: Chuanxiao Dong <chuanxiao.dong@xxxxxxxxx> > > Signed-off-by: Yunpeng Gao <yunpeng.gao@xxxxxxxxx> > > --- > > drivers/mmc/core/mmc.c | 19 +++++++++++++++++++ > > include/linux/mmc/host.h | 1 + > > 2 files changed, 20 insertions(+) > > > > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c index > > 793c6f7..13a5b24 100644 > > --- a/drivers/mmc/core/mmc.c > > +++ b/drivers/mmc/core/mmc.c > > @@ -1000,6 +1000,25 @@ static int mmc_select_hs_ddr(struct mmc_card > *card) > > return err; > > } > > > > + /* > > + * Even eMMC 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. > > + * > > + * If a host controller cannot support 3.3v for DDR, try 1.8v > > + */ > > + if (unlikely(host->caps2 & MMC_CAP2_NO_3_3V_DDR)) { > > + if (card->mmc_avail_type & > EXT_CSD_CARD_TYPE_HS200_1_8V) { > > + err = __mmc_set_signal_voltage(host, > > + > MMC_SIGNAL_VOLTAGE_180); > > + if (err) > > + return err; > > + } else > > + return -EOPNOTSUPP; > > + } > > I am wondering if we could try an another approach while changing signal > voltage for (e)MMC. Simply start by trying with 1.2V, then 1.8V and then 3.3V. > Obviously we shouldn't try with something that isn't supported, which > card->mmc_avail_type tells us about. > > I realize that it will mean a change in behaviour and depending on how hosts > are handling signal voltage, this is a bit uncertain if it would work. Still I feel it > would be the right approach. Can we give at shot? I agree with you. Actually this is also out original approach. :) Given it we cannot test this approach on all host controllers, thus finally change to add a new CAP is to avoid impacting other host controllers. I can post a v2 patch to implement this IO signal voltage changing sequence for review. Thanks Chuanxiao > > Kind regards > Uffe > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body > of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at > http://vger.kernel.org/majordomo-info.html ��.n��������+%������w��{.n�����{��i��)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
