Re: [PATCH 04/23] mmc: sdhci: re-factor sdhci_start_signal_voltage()

[Dong Aisheng <dongas86@gmail.com>]

On Thu, Apr 28, 2016 at 09:39:54AM +0300, Adrian Hunter wrote:
> On 28/04/16 06:09, Dong Aisheng wrote:
> > On Wed, Apr 27, 2016 at 11:26:52PM +0300, Adrian Hunter wrote:
> >> On 24/04/2016 12:14 p.m., Dong Aisheng wrote:
> >>> Hi Adrian,
> >>>
> >>> Thanks for the review first.
> >>>
> >>> On Fri, Apr 22, 2016 at 7:43 PM, Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>> On 15/04/16 20:29, Dong Aisheng wrote:
> >>>>> Handle host and regulator signal voltage switch separately.
> >>>>> Move host signal voltage switch code into a separated function
> >>>>> sdhci_do_signal_voltage_switch() first, the following patches will
> >>>>> remove the regulator voltage switch code and use the common
> >>>>> mmc_regulator_set_vqmmc() instead.
> >>>>
> >>>> You have changed the order that things are done.
> >>>
> >>> Yes, the oder changes a bit that we always do controller voltage switch first.
> >>> I suppose the order is irrelevant here since i don't recall any
> >>> requirement from card.
> >>>
> >>> Actually the original order is also a bit mass.
> >>> e.g.
> >>> For MMC_SIGNAL_VOLTAGE_330, switch controller first, then vqmmc.
> >>> But for MMC_SIGNAL_VOLTAGE_180, switch vqmmc first, then controller.
> >>> It looks to us the original one also order irrelevant.
> >>>
> >>>> There is no way to know
> >>>> what that will break, so let's not do that.  What about just changing
> >>>> regulator_set_voltage() to mmc_regulator_set_vqmmc()?
> >>>>
> >>>
> >>> Currently what i can think out VIO switch using are three cases: (Pls
> >>> help add if any)
> >>> 1) Both host IO and card IO use external vqmmc to do switch
> >>> (e.g eMMC 1.8V DDR/HS200/HS400 mode)
> >>>
> >>> eMMC has no IO voltage switch protocol and requirement, so usually
> >>> board designed
> >>> using fixed 1.8V for eMMC and host IO.
> >>> Event it's switchable, it should be done in the first mmc_power_up().
> >>> Dynamical switch later may cause eMMC unable to work properly.
> >>> (We have been confirmed about this issue by many eMMC vendors
> >>> like Micron and Sandisk. I'm not sure if any exceptions in the community
> >>> still doing VIO dynamical switch for eMMC, if yes, please help share
> >>> the experience!).
> >>>
> >>> Event some people still do dynamical IO switch for eMMC, since eMMC
> >>> spec has no requirement, so the order should also not care.
> >>>
> >>> 2) Host using controller IO switch while card using standard CMD (SD/SDIO3.0)
> >>>
> >>> SD/SDIO 3.0 spec defines the standard IO switch process and using it's internal
> >>> regulator to do card IO voltage switch. It does not use external vqmmc
> >>> regulator.
> >>> So order irrelevant too.
> >>>
> >>> 3) Host using controller IO switch while card using external vqmmc
> >>> (special SDIO3.0 or eMMC)
> >>> I have met some special SDIO3.0 card like Broadcom WiFi which does not follow
> >>> the spec and using external regulator for card IO voltage.
> >>> Usually it's required to fix to 1.8v and also not order irrelevant.
> >>>
> >>> For eMMC, refer to case 1), it should be fixed to 1.8v at power up.
> >>>
> >>> So it looks all cases seems are not order required.
> >>
> >> I don't agree that there is any way to know that other host controllers
> >> are not affected.  I don't want a repeat of sdhci_set_power().
> >>
> > 
> > Can you share some more info about sdhci_set_power() issue?
> > I'd like to see if we are same the issue.
> 
> Not the same issue, but the same concept.  People changing the code under
> the impression that their way was correct, and then breaking other people's
> drivers.  Check the git history and mailing list.
> 
> 	http://marc.info/?l=linux-mmc&m=145880454106474&w=2
> 

Yes, now i understand your concern.

> > 
> > BTW, IMHO i don't think we should stop keep moving only afraid of potential
> > break if it's correct way. Because .start_signal_voltage_switch() interface
> > seems shouldn't be order dependant.
> > If it is, then it should be fixed and handled in high layer like MMC core
> > rather than in host driver. Right?
> 
> The SDHCI spec. does not define how to use external regulators, so there is
> no "correct way".
> 

The "correct way" i mean here is .start_signal_voltage_switch() shouldn't be
order dependant, would you agree?

> We have to move forward *and* avoid potential breakage.
> 

If really break happens, fix platform driver, not common SDHCI.
That's the same thing you done for sdhci_set_power().

> In this case it seems me that the risk of breakage outweighs the value of
> prettier code.
> 

Actually my main purpose is patch 6: using mmc_regulator_set_vqmmc()
which is worth and it does improve the stability and eliminate the
potential signal issue.
However it's not the same way as you proposed.
See below.

> By the way, there are ways to get rid of the ugliness - such as pushing it down
> into individual drivers.
> 
> > 
> >> Please instead send a patch for just using mmc_regulator_set_vqmmc()
> >> in place of regulator_set_voltage().
> > 
> > Just using mmc_regulator_set_vqmmc() also changes the order which
> > is the same situation.
> 
> How so?  It looks like a drop-in replacement to me:
> 

Sorry, i did not get that you want to change like below.
However, it looks that it does not make too much sense to call
mmc_regulator_set_vqmmc() for each VOLTAGE type like 3.3v/1.8v/1.2v
which introduces ugliness because mmc_regulator_set_vqmmc()
already handles it internally, right?
Only because we want to keep an "ASSUMED" order as before?

Regards
Dong Aisheng

> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 94cffa77490a..69b4d48aff87 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1757,8 +1757,7 @@ static int sdhci_do_start_signal_voltage_switch(struct sdhci_host *host,
>  		sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
>  
>  		if (!IS_ERR(mmc->supply.vqmmc)) {
> -			ret = regulator_set_voltage(mmc->supply.vqmmc, 2700000,
> -						    3600000);
> +			ret = mmc_regulator_set_vqmmc(mmc, ios);
>  			if (ret) {
>  				pr_warn("%s: Switching to 3.3V signalling voltage failed\n",
>  					mmc_hostname(mmc));
> @@ -1779,8 +1778,7 @@ static int sdhci_do_start_signal_voltage_switch(struct sdhci_host *host,
>  		return -EAGAIN;
>  	case MMC_SIGNAL_VOLTAGE_180:
>  		if (!IS_ERR(mmc->supply.vqmmc)) {
> -			ret = regulator_set_voltage(mmc->supply.vqmmc,
> -					1700000, 1950000);
> +			ret = mmc_regulator_set_vqmmc(mmc, ios);
>  			if (ret) {
>  				pr_warn("%s: Switching to 1.8V signalling voltage failed\n",
>  					mmc_hostname(mmc));
> @@ -1810,8 +1808,7 @@ static int sdhci_do_start_signal_voltage_switch(struct sdhci_host *host,
>  		return -EAGAIN;
>  	case MMC_SIGNAL_VOLTAGE_120:
>  		if (!IS_ERR(mmc->supply.vqmmc)) {
> -			ret = regulator_set_voltage(mmc->supply.vqmmc, 1100000,
> -						    1300000);
> +			ret = mmc_regulator_set_vqmmc(mmc, ios);
>  			if (ret) {
>  				pr_warn("%s: Switching to 1.2V signalling voltage failed\n",
>  					mmc_hostname(mmc));
> 
> 
>