> -----Original Message-----
> From: Gao, Yunpeng
> Sent: Monday, August 18, 2014 2:17 PM
> To: linux-mmc@xxxxxxxxxxxxxxx
> Cc: Gao, Yunpeng; Dong, Chuanxiao
> Subject: [PATCH] mmc: core: optimize mmc device power up ramp up time
>
> In current kernel mmc driver, it uses two 'msleep(10)'
> for eMMC/SD card power up ramp up time delay.
>
> According to Spec, the ramp up time should be max of 74 eMMC/SD bus clock
> or 1ms.
> Take the worst eMMC/SD card I can image as the example - assume it has to
> work on 32KHz or 16KHz during the card initialzation, then 74 clock should be
> 2.312ms or 4.625ms.
> So, 5ms delay should be enough.
>
> Also, msleep(10) will invlove sechdule and may consume more time than what
> we expected.
> Measured on Merrifield platform showed it consumed almost
> 2*20 = 40ms. This is much more than what we expected.
>
> Submit this patch to reduce the time of mmc boot up and the time of mmc D3
> resume.
>
> Signed-off-by: Yunpeng Gao <yunpeng.gao@xxxxxxxxx>
> Signed-off-by: Chuanxiao Dong <chuanxiao.dong@xxxxxxxxx>
> ---
> 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
> 7dc0c85..7bcb797 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1556,7 +1556,7 @@ 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);
> + usleep_range(10000, 12000);
Instead of directly change the mmc_delay to usleep_range, I prefer to do it in changing the drivers/mmc/core/core.h:
diff --git a/drivers/mmc/core/core.h b/drivers/mmc/core/core.h
index 443a584..b7584d8 100644
--- a/drivers/mmc/core/core.h
+++ b/drivers/mmc/core/core.h
@@ -55,9 +55,10 @@ static inline void mmc_delay(unsigned int ms)
if (ms < 1000 / HZ) {
cond_resched();
mdelay(ms);
- } else {
+ } else if (ms < 20)
+ usleep_range(ms * 1000, (ms + 1) * 1000);
+ else
msleep(ms);
- }
}
Thanks
Chuanxiao
>
> host->ios.clock = host->f_init;
>
> @@ -1567,7 +1567,7 @@ 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);
> + usleep_range(5000, 6000);
>
> mmc_host_clk_release(host);
> }
> --
> 1.7.9.5
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