Hi Phil, On 05/26/2017 05:01 PM, Phil Edworthy wrote: > Hi Jaehoon Chung, > > On 26 May 2017 04:38 Jaehoon Chung wrote: >> On 05/25/2017 11:14 PM, Phil Edworthy wrote: >>> 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. > f_min is not the frequency that must be used during init, it is the minimum > frequency that the Controller can operate at. If a controller has f_min=300KHz > then there is no problem attempting to set the MMC clock to 400KHz. If the > controller cannot do exactly 400KHz, the driver should set the clock to the > closest frequency _under_ 400KHz. > > For example, SDHCI v3 controllers set f_min to f_max / 2046. In my particular > case, SDHCI v3 controller f_max is 50MHz, so f_min is approximately 25KHz. > Therefore, when the code does this: > mmc_set_clock(mmc, 1); > it will set the clock rate to approximately 25KHz. > Clearly this is outside the valid 100-400KHz range that you quote.
Well..then i will check the real frequency with oscilloscope.. then it's more clear than now.. :) Thanks for pointing out about this. Best Regards, Jaehoon Chung > > Thanks > Phil > >>> 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
