On 05/25/2017 11:14 PM, Phil Edworthy wrote: > Hi Jaehoon Chung, > > On 25 May 2017 15:10 Jaehoon Chung wrote: >> On 05/25/2017 11:02 PM, Phil Edworthy wrote: >>> On 25 May 2017 14:50 Jaehoon Chung wrote: >>>> On 05/24/2017 10:54 PM, Phil Edworthy wrote: >>>>> The code currently defaults to the slowest clock speed that can be >>>>> achieved, which can be significantly lower than the SD spec. >>>> >>>> Is there any problem..As i know, it should be changed from 1 to min_clk. >>> The only problem is that the initial SD clock can be very slow so it >>> increases the time to start SD. Admittedly, it's a very small increase >>> in time, but we should use the correct initial clock speed. >> >> Well..i didn't agree yet... >> >> If mmc_set_clock(mmc, 400K) and mmc->cfg->f_min is 300K? >> Initial clock should be always 400K..but spec is mentioned "initial clock is >> maximum 400K.." >> It means the clock can be the value under 400K. > I'm not sure I follow you. > The spec means that all SD cards must support an initial clock speed of > 400KHz, right?
No..clock frequency range shall be 100KHz - 400KHz during initialization sequence. Some targets should not work fine with 400KHz..So it needs to check f_min value. otherwise, it needs to find the initial clock value like Linux kernel scheme. > If so, then there is no harm in setting it to 400KHz. > > Thanks > Phil > >>>>> Signed-off-by: Phil Edworthy <phil.edwor...@renesas.com> >>>>> --- >>>>> drivers/mmc/mmc.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index >>>>> 72fc177..dff1be3 100644 >>>>> --- a/drivers/mmc/mmc.c >>>>> +++ b/drivers/mmc/mmc.c >>>>> @@ -1676,7 +1676,7 @@ int mmc_start_init(struct mmc *mmc) #endif >>>>> mmc->ddr_mode = 0; >>>>> mmc_set_bus_width(mmc, 1); >>>>> - mmc_set_clock(mmc, 1); >>>>> + mmc_set_clock(mmc, 400000); >>>>> >>>>> /* Reset the Card */ >>>>> err = mmc_go_idle(mmc); >>>>> >>> >>> >>> >>> > > > > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
