On 2018/4/20 17:07, Ulf Hansson wrote:
On 20 April 2018 at 10:03, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
This reverts commit 79bccc5aefb4e64e651abe04f78c3e6bf8acd6f0.
The intention for this revert is that the 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.
I fully agree with this reasoning.
In practise, the modern hardware should have a stable power supply
with 1ms after setting it for no matter PMIC or discrete power. But
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.
It has been long time proved 2ms is enough when testing variety of
boards. If it finally turned out some boards need more than 2ms here,
the best we should do is to ask folks to get that period of time from
firmware node, for instance DT, and implement ->set_voltage_time_sel()
for the regulaor used, but not bother mmc core again.
This is true if there is an external regulator, but sometimes we use
host specific ways to power the card.
Just revert it now and see if it could smokes out something interesting.
And what to when/if there are errors reported? Revert the revert? :-)
The 2ms was there in 2009, so it's not like it has recently changed to
10 ms. I am not really comfortable to change it like this. >
yes, that's why it's just a RFC that we could have disscussions
based on code. :)
An option is to use an opt-out method, perhaps via a new host cap?
Maybe we should allow a more scaleable method, for instance, ask
host drivers to reported a desired delay if wanted, but fall back to
use 10ms by default if not?
Kind regards
Uffe
Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
---
Not sure if Toshiba Tecra M5 is still supported for upstream kernel
or if there are real users now.
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 121ce50..b154518 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1658,7 +1658,7 @@ 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(2);
mmc_pwrseq_post_power_on(host);
@@ -1671,7 +1671,7 @@ 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(2);
}
void mmc_power_off(struct mmc_host *host)
--
1.9.1
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