On 24 April 2014 23:44, Tim Kryger <tim.kryger@xxxxxxxxxx> wrote: > The eMMC signalling voltage is determined by VCCQ which is provided to > the card by the host. Signalling is not required to begin at 3.3v and, > if the host and card both support a particular VCC/VCCQ combination, it > can be used immediately. > > In contrast, SD Cards must begin with 3.3v signalling and may switch to > a lower voltage signalling if instructed to do so in CMD11. A message > is required to coordinate this operation because the card only receives > a 3.3v VDD and must know when to use the 1.8v produced by its internal > regulator. > > It makes sense for the core to begin with 3.3v signalling but when that > can't be set, 1.8v and 1.2v signalling also should be attempted. This > is especially important when an external regulator with a limited range > is used to supply VCCQ to an eMMC part. > > Signed-off-by: Tim Kryger <tim.kryger@xxxxxxxxxx> Acked-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > --- > > Changes since v1: > - Eliminated temporary err variable and added debug output > > drivers/mmc/core/core.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c > index acbc3f2..72926a9 100644 > --- a/drivers/mmc/core/core.c > +++ b/drivers/mmc/core/core.c > @@ -1533,8 +1533,13 @@ void mmc_power_up(struct mmc_host *host, u32 ocr) > host->ios.timing = MMC_TIMING_LEGACY; > mmc_set_ios(host); > > - /* Set signal voltage to 3.3V */ > - __mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_330); > + /* Try to set signal voltage to 3.3V but fall back to 1.8v or 1.2v */ > + if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_330) == 0) > + dev_dbg(mmc_dev(host), "Initial signal voltage of 3.3v\n"); > + else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180) == 0) > + dev_dbg(mmc_dev(host), "Initial signal voltage of 1.8v\n"); > + else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_120) == 0) > + dev_dbg(mmc_dev(host), "Initial signal voltage of 1.2v\n"); > > /* > * This delay should be sufficient to allow the power supply > -- > 1.7.9.5 > -- 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
