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.edworthy@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);