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

Doug Anderson dianders at chromium.org
Wed Feb 25 13:05:13 PST 2015


On Tue, Feb 24, 2015 at 11:52 PM, Alim Akhtar <alim.akhtar at 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 " 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


More information about the Linux-rockchip mailing list