Re: [PATCH RFC 1/2] mmc: sdhci: Allow platform controlled voltage switching

[Vijay Viswanath]

On 7/10/2018 4:37 PM, Adrian Hunter wrote:
> On 21/06/18 15:23, Vijay Viswanath wrote:
> > Some controllers can have internal mechanism to inform the SW that it
> > is ready for voltage switching. For such controllers, changing voltage
> > before the HW is ready can result in various issues.
> >
> > Add a quirk, which can be used by drivers of such controllers.
> >
> > Signed-off-by: Vijay Viswanath <vviswana@xxxxxxxxxxxxxx>
> > ---
> >   drivers/mmc/host/sdhci.c | 20 +++++++++++++++-----
> >   drivers/mmc/host/sdhci.h |  2 ++
> >   2 files changed, 17 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index 1c828e0..f0346d4 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -1615,7 +1615,8 @@ void sdhci_set_power_noreg(struct sdhci_host *host, unsigned char mode,
> >   void sdhci_set_power(struct sdhci_host *host, unsigned char mode,
> >   		     unsigned short vdd)
> >   {
> > -	if (IS_ERR(host->mmc->supply.vmmc))
> > +	if (IS_ERR(host->mmc->supply.vmmc) ||
> > +			(host->quirks2 & SDHCI_QUIRK2_INTERNAL_PWR_CTL))
>
> I think you should provide your own ->set_power() instead of this

will do

> >   		sdhci_set_power_noreg(host, mode, vdd);
> >   	else
> >   		sdhci_set_power_reg(host, mode, vdd);
> > @@ -2009,7 +2010,9 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> >   		ctrl &= ~SDHCI_CTRL_VDD_180;
> >   		sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
> >   
> > -		if (!IS_ERR(mmc->supply.vqmmc)) {
> > +		if (!IS_ERR(mmc->supply.vqmmc) &&
> > +				!(host->quirks2 &
> > +					SDHCI_QUIRK2_INTERNAL_PWR_CTL)) {
>
> And your own ->start_signal_voltage_switch()

sdhci_msm_start_signal_voltage_switch() would be an exact copy of 
sdhci_start_signal_voltage_switch()..... will incorporate this if not 
using quirk.

> >   			ret = mmc_regulator_set_vqmmc(mmc, ios);
> >   			if (ret) {
> >   				pr_warn("%s: Switching to 3.3V signalling voltage failed\n",
> > @@ -2032,7 +2035,8 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> >   	case MMC_SIGNAL_VOLTAGE_180:
> >   		if (!(host->flags & SDHCI_SIGNALING_180))
> >   			return -EINVAL;
> > -		if (!IS_ERR(mmc->supply.vqmmc)) {
> > +		if (!IS_ERR(mmc->supply.vqmmc) &&
> > +			!(host->quirks2 & SDHCI_QUIRK2_INTERNAL_PWR_CTL)) {
> >   			ret = mmc_regulator_set_vqmmc(mmc, ios);
> >   			if (ret) {
> >   				pr_warn("%s: Switching to 1.8V signalling voltage failed\n",
> > @@ -3485,7 +3489,10 @@ int sdhci_setup_host(struct sdhci_host *host)
> >   	 * the host can take the appropriate action if regulators are not
> >   	 * available.
> >   	 */
> > -	ret = mmc_regulator_get_supply(mmc);
> > +	if (!(host->quirks2 & SDHCI_QUIRK2_INTERNAL_PWR_CTL))
>
> Since we expect mmc_regulator_get_supply() to have been called, this could be:
>
> 	if (!mmc->supply.vmmc) {
> 		ret = mmc_regulator_get_supply(mmc);
> 		enable_vqmmc = true;
> 	} else {
> 		ret = 0;
> 	}
> >> +		ret = mmc_regulator_get_supply(mmc);
> > +	else
> > +		ret = 0;
> >   	if (ret)
> >   		return ret;
> >   
> > @@ -3736,7 +3743,10 @@ int sdhci_setup_host(struct sdhci_host *host)
> >   
> >   	/* If vqmmc regulator and no 1.8V signalling, then there's no UHS */
> >   	if (!IS_ERR(mmc->supply.vqmmc)) {
> > -		ret = regulator_enable(mmc->supply.vqmmc);
> > +		if (!(host->quirks2 & SDHCI_QUIRK2_INTERNAL_PWR_CTL))
>
> And this could be:
>
> 		if (enable_vqmmc)
> 			ret = regulator_enable(mmc->supply.vqmmc);
> 		else
> 			ret = 0;
>  > However, you still need to ensure regulator_disable(mmc->supply.vqmmc) is
> only called if regulator_enable() was called.
I missed this. Will cover it.

Also I missed one more place where we are doing regulator_disable. 
During sdhci-msm unbinding, we would end up doing an extra regulator 
disable (thanks Evan for pointing it out) in sdhci_remove_host.

To avoid the quirk( or having any flag), it would require copying the 
code of sdhci_start_signal_voltage_switch() and sdhci_remove_host() and 
creating 2 new functions in sdhci_msm layer which would do the exact 
same as above, with just the regulator parts removed.

This looks messy (considering any future changes to the 2 sdhci API will 
need to be copied to their duplicate sdhci_msm API) and a bit overkill 
to avoid quirk. At the same time, I don't know how useful such a quirk 
would be to other platform drivers.

Please let me know your view/suggestions.
> > +			ret = regulator_enable(mmc->supply.vqmmc);
> > +		else
> > +			ret = 0;
> >   		if (!regulator_is_supported_voltage(mmc->supply.vqmmc, 1700000,
> >   						    1950000))
> >   			host->caps1 &= ~(SDHCI_SUPPORT_SDR104 |
> > diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> > index 23966f8..3b0c97a 100644
> > --- a/drivers/mmc/host/sdhci.h
> > +++ b/drivers/mmc/host/sdhci.h
> > @@ -450,6 +450,8 @@ struct sdhci_host {
> >    * obtainable timeout.
> >    */
> >   #define SDHCI_QUIRK2_DISABLE_HW_TIMEOUT			(1<<17)
> > +/* Regulator voltage changes are being done from platform layer */
> > +#define SDHCI_QUIRK2_INTERNAL_PWR_CTL				(1<<18)
>
> So maybe the quirk is not needed.
>
> >   
> >   	int irq;		/* Device IRQ */
> >   	void __iomem *ioaddr;	/* Mapped address */

Thanks for the review & suggestions!
Vijay