On 23/04/18 10:33, Shawn Lin wrote:
> Hi Adrain,
>
> On 2018/4/23 14:24, Adrian Hunter wrote:
>> 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.
>>
>
> The main concern is if a driver didn't call mmc_of_parse, so
> host->ios.power_delay_ms is zero along with allocating host.
> But it will be broken if the board/platform happened to rely on
> previous 10ms delay in mmc core layer. That being said, I don't
> know if the zero value comes from explicitly assigement or
> kzalloc(host).
>
> Do I misunderstand your point?
Well it can be set to 10ms when the host is allocated.
>
>>> 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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>>
>
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