On 21/04/18 11:03, Shawn Lin wrote:
> The hard-coded 10ms delay in mmc_power_up came from
> commit 79bccc5aefb4 ("mmc: increase power up delay"), which said "The TI
> controller on Toshiba Tecra M5 needs more time to power up or the cards
> will init incorrectly or not at all." But 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.
>
> However, it's added since 2009, and we can't tell if other platforms
> benefit from it. But in practise, the modern hardware are most likely to
> have a stable power supply with 1ms after setting it for no matter PMIC
> or discrete power. And 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. Of course, if there
> are some other ways for host to power the card, we should allow them
> to argue a suitable delay as well.
>
> With this patch, we could assign the delay from firmware, or we could
> assigne it via ->set_ios() callback from host drivers.
>
> Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> ---
>
> drivers/mmc/core/core.c | 6 ++++--
> drivers/mmc/core/host.c | 4 ++++
> include/linux/mmc/host.h | 1 +
> 3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 121ce50..04d3cf4 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1027,6 +1027,8 @@ void mmc_set_initial_state(struct mmc_host *host)
> host->ios.bus_width = MMC_BUS_WIDTH_1;
> host->ios.timing = MMC_TIMING_LEGACY;
> host->ios.drv_type = 0;
> + if (!host->ios.power_delay_ms)
> + host->ios.power_delay_ms = 10;
Some drivers already have delays, so a zero value should be supported IMHO.
> host->ios.enhanced_strobe = false;
>
> /*
> @@ -1658,7 +1660,7 @@ 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(host->ios.power_delay_ms);
>
> mmc_pwrseq_post_power_on(host);
>
> @@ -1671,7 +1673,7 @@ 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(host->ios.power_delay_ms);
> }
>
> void mmc_power_off(struct mmc_host *host)
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index 64b03d6..9c34063 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -338,6 +338,10 @@ int mmc_of_parse(struct mmc_host *host)
> host->dsr_req = 0;
> }
>
> + if (device_property_read_u32(dev, "power-delay-ms",
> + &host->ios.power_delay_ms))
> + host->ios.power_delay_ms = 0;
> +
> return mmc_pwrseq_alloc(host);
> }
>
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 7c6eaf6..efa9bab 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -22,6 +22,7 @@
> struct mmc_ios {
> unsigned int clock; /* clock rate */
> unsigned short vdd;
> + unsigned int power_delay_ms; /* waiting for stable power */
>
> /* vdd stores the bit number of the selected voltage range from below. */
>
>
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