On 20 April 2018 at 10:03, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote: > This reverts commit 79bccc5aefb4e64e651abe04f78c3e6bf8acd6f0. > > The intention for this revert is that the it's too engineering > solution for a special board but force all platforms to wait > for that long time, especially painful for mmc_power_up for eMMC > when booting. I fully agree with this reasoning. > > In practise, the modern hardware should have a stable power supply > with 1ms after setting it for no matter PMIC or discrete power. But > more importnatly, most regulators implement the callback of > ->set_voltage_time_sel() for regulator core to wait for specific > period of time for the power supply to be stable, which means once > regulator_set_voltage_* return, the power should reach the the minimum > voltage that works for initialization. > > It has been long time proved 2ms is enough when testing variety of > boards. If it finally turned out some boards need more than 2ms here, > the best we should do is to ask folks to get that period of time from > firmware node, for instance DT, and implement ->set_voltage_time_sel() > for the regulaor used, but not bother mmc core again. This is true if there is an external regulator, but sometimes we use host specific ways to power the card. > > Just revert it now and see if it could smokes out something interesting. And what to when/if there are errors reported? Revert the revert? :-) The 2ms was there in 2009, so it's not like it has recently changed to 10 ms. I am not really comfortable to change it like this. An option is to use an opt-out method, perhaps via a new host cap? Kind regards Uffe > > Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> > --- > Not sure if Toshiba Tecra M5 is still supported for upstream kernel > or if there are real users now. > > drivers/mmc/core/core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c > index 121ce50..b154518 100644 > --- a/drivers/mmc/core/core.c > +++ b/drivers/mmc/core/core.c > @@ -1658,7 +1658,7 @@ void mmc_power_up(struct mmc_host *host, u32 ocr) > * This delay should be sufficient to allow the power supply > * to reach the minimum voltage. > */ > - mmc_delay(10); > + mmc_delay(2); > > mmc_pwrseq_post_power_on(host); > > @@ -1671,7 +1671,7 @@ void mmc_power_up(struct mmc_host *host, u32 ocr) > * This delay must be at least 74 clock sizes, or 1 ms, or the > * time required to reach a stable voltage. > */ > - mmc_delay(10); > + mmc_delay(2); > } > > void mmc_power_off(struct mmc_host *host) > -- > 1.9.1 > > -- 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
