Re: [PATCH v4 1/3] mmc: dw_mmc: update clock after host reach a stable voltage

Doug Anderson
2015-02-25T21:05:13Z

Alim,

On Tue, Feb 24, 2015 at 11:52 PM, Alim Akhtar <alim.akhtar@gmail.com> wrote:
>>> This looks a HACK to me.
>>> If stabilizing host voltage regulator is the problem, can you try out
>>> below patch, and see if this resolve your issue?
>>
>> Actually, IMHO Alim's patch is more of a hack than Addy's. There's
>> already a 10ms delay between "power up" and "power on" in the MMC core
>> in mmc_power_up() state. That delay is commented as:
>>
> Well, my suggestion (adding 5ms in switch_volatge) was based on DW_MMC
> databook (V2.41a) section "7.4.1.2 Voltage switch Normal Scenario"
> step #7 which says:" After the 5ms timer expires, the host voltage
> regulator is stable".

So all of that should be handled by the core. Just reading the DW_MMC
databook can be confusing because they don't differentiate between
what's in the SDMMC spec and what's DW_MMC specific.

Check out mmc_set_signal_voltage(), specifically:

* During a signal voltage level switch, the clock must be gated
* for 5 ms according to the SD spec

-Doug