[PATCH v3 2/7] mmc: mediatek: Add Mediatek MMC driver

[Chaotian Jing]

On Fri, 2015-05-08 at 14:12 +0200, Ulf Hansson wrote:
> On 7 May 2015 at 03:42, Chaotian Jing <chaotian.jing at mediatek.com> wrote:
> > Dear Ulf,
> >
> > Thanks!
> > Below is my comment:
> >
> > On Wed, 2015-05-06 at 18:31 +0200, Ulf Hansson wrote:
> >> On 6 May 2015 at 08:54, chaotian.jing <chaotian.jing at mediatek.com> wrote:
> >> > Dear Ulf,
> >> >
> >> > Thanks for your review.
> >> > I must do a explain of our MMC host:
> >> > Source clock is source clock of the MMC bus, MMC host has a divider to
> >> > get different bus clock frequency. now the runtime suspend is gating
> >> > this clock.
> >> >
> >> > Hclk is the power domain of the MMC host, if Hclk is gated, the MMC host
> >> > cannot work(all registers readout is zero). and, all registers would be
> >> > reset to default value if Hclk is gated/ungated.
> >> > At MT8173, MSDC0 and MSDC2 has independent Hclk, MSDC1 and MSDC3's Hclk
> >> > was controlled by "Infra module".
> > Sorry for mistake, MSDC0 and MSDC3 has independent Hclk, MSDC1 and
> > MSDC2's Hclk was controlled by "Infra module". the Infra module is a
> > "power saving module", when the system go to sleep, Infra module will be
> > set and MSDC1 & MSDC2's Hclk will be gated automatically.
> >>
> >> Thanks for clarifying!
> >>
> >> I don't have enough knowledge about your SoC to understand the detail,
> >> but it seems like we are mixing clocks and power domains. I would
> >> rather keep this separate - if the HW allows it.
> >>
> >> I guess the key question I have is the following:
> >> 1) Is it hardware wise possible to gate the hclk, but without gating
> >> the power domain?
> >> 2) At what level is the reference counting done for each device in the
> >> power domain? In HW or in sofftware?
> >>
> >
> > Actually, Our MMC host do not have power domain, all the control of the
> > host is the Hclk.
> 
> Okay, but I am not sure that fully answered my question.
> 
> You said that hclk will be gated when the power domain gets gated. And
> the power domain (infra module, right?) will be gated at system PM
> sleep. And when that happens the mmc controller loses register
> context.
> 
> But, again, can hclk be gated without gating the power domain?
> 
> No matter what, it seems like a good idea to gate the power domain
> when all clients of it are idle. Yes we would need to manage register
> save/restore context, but on the other hand allow you to save more
> power, right?
> 
For MSDC0 & MSDC3, it has independent HCLK, do not have power domain.
For MSDC1 & MSDC2, its HCLK was controlled by Infra module(This is a big
power domain for many modules).
So, for msdc0 & msdc3, we can control its Hclk, for msdc1 & msdc2, we
cannot control it.

Yes, I will do gate/ungate HCLK & source clock in PM.
In addition, Since the gate/ungate HCLK is done by runtime PM, and all
register operation should work at HCLK is on, so the msdc_init_hw() only
can be called at set_ios(), because in probe(), the HCLK may have not
been enabled.
> Kind regards
> Uffe