Date:   Tue, 31 Jul 2018 14:59:38 +0300
From:   Aapo Vienamo <avienamo@...dia.com>
To:     Stefan Agner <stefan@...er.ch>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-tegra-owner@...r.kernel.org>
Subject: Re: [PATCH v2 03/10] mmc: tegra: Reconfigure pad voltages during
 voltage switching

On Tue, 31 Jul 2018 11:15:41 +0200
Stefan Agner <stefan@...er.ch> wrote:

> On 27.07.2018 10:44, Aapo Vienamo wrote:
> > On Thu, 26 Jul 2018 15:33:11 +0200
> > Stefan Agner <stefan@...er.ch> wrote:
> >   
> >> On 26.07.2018 14:19, Aapo Vienamo wrote:  
> >> > Parse the pinctrl state and nvidia,only-1-8-v properties from the device
> >> > tree and implement pad voltage state reconfiguration in the mmc
> >> > start_signal_voltage_switch() callback. Validate the pinctrl and
> >> > regulator configuration before unmasking UHS modes. Add
> >> > NVQUIRK_NEEDS_PAD_CONTROL and add set it for Tegra210 and Tegra186.
> >> >
> >> > The pad configuration is done in the mmc callback because the order of
> >> > pad reconfiguration and sdhci voltage switch depend on the voltage to
> >> > which the transition occurs.
> >> >
> >> > Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> >> > ---
> >> >  drivers/mmc/host/sdhci-tegra.c | 140 +++++++++++++++++++++++++++++++++++++----
> >> >  1 file changed, 127 insertions(+), 13 deletions(-)
> >> >
> >> > diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> >> > index ddf00166..9587365 100644
> >> > --- a/drivers/mmc/host/sdhci-tegra.c
> >> > +++ b/drivers/mmc/host/sdhci-tegra.c
> >> > @@ -21,6 +21,7 @@
> >> >  #include <linux/io.h>
> >> >  #include <linux/of.h>
> >> >  #include <linux/of_device.h>
> >> > +#include <linux/pinctrl/consumer.h>
> >> >  #include <linux/reset.h>
> >> >  #include <linux/mmc/card.h>
> >> >  #include <linux/mmc/host.h>
> >> > @@ -55,6 +56,7 @@
> >> >  #define NVQUIRK_ENABLE_SDR104		BIT(4)
> >> >  #define NVQUIRK_ENABLE_DDR50		BIT(5)
> >> >  #define NVQUIRK_HAS_PADCALIB		BIT(6)
> >> > +#define NVQUIRK_NEEDS_PAD_CONTROL	BIT(7)
> >> >
> >> >  struct sdhci_tegra_soc_data {
> >> >  	const struct sdhci_pltfm_data *pdata;
> >> > @@ -66,8 +68,13 @@ struct sdhci_tegra {
> >> >  	struct gpio_desc *power_gpio;
> >> >  	bool ddr_signaling;
> >> >  	bool pad_calib_required;
> >> > +	bool pad_control_available;
> >> > +	bool only_1v8;
> >> >
> >> >  	struct reset_control *rst;
> >> > +	struct pinctrl *pinctrl_sdmmc;
> >> > +	struct pinctrl_state *pinctrl_state_3v3;
> >> > +	struct pinctrl_state *pinctrl_state_1v8;
> >> >  };
> >> >
> >> >  static u16 tegra_sdhci_readw(struct sdhci_host *host, int reg)
> >> > @@ -138,12 +145,47 @@ static unsigned int tegra_sdhci_get_ro(struct
> >> > sdhci_host *host)
> >> >  	return mmc_gpio_get_ro(host->mmc);
> >> >  }
> >> >
> >> > +static bool tegra_sdhci_is_uhs_valid(struct sdhci_host *host)
> >> > +{
> >> > +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >> > +	struct sdhci_tegra *tegra_host = sdhci_pltfm_priv(pltfm_host);
> >> > +	const struct sdhci_tegra_soc_data *soc_data = tegra_host->soc_data;
> >> > +
> >> > +	/*
> >> > +	 * The 1.8 V only host controllers don't need to have configurable
> >> > +	 * regulators and pad voltages. In this case the UHS modes can be
> >> > +	 * enabled regardless.
> >> > +	 */
> >> > +	if (tegra_host->only_1v8)
> >> > +		return true;  
> >>
> >> Hm, SD always needs 3.3V capabilities, not?  
> > 
> > Yes, the controllers used for eMMCs should have the only_1v8 property
> > set and they exit the function here. With controllers used for SD cards,
> > the regulator and pad configurations are verified later in the function.
> >   
> 
> By returning true you ask the controller to enable UHS modes. However,
> if you have 1.8V only, there should be no UHS modes advertised (since SD
> cards require 1.8V).
> 
> That assumes that UHS modes are a SD card thing only (which I think
> strictly speaking should be the case).
> 
> However, at least on Tegra 3 it seems that enabling SD 3.0 is also
> required for higher eMMC speeds:
> https://patchwork.kernel.org/patch/10521147/
> 
> So UHS is probably not so much about SD card UHS modes but more about
> higher speed modes in general...

True.

> >> So if the controller is 1.8V only, then only eMMC modes are allowed.
> >>
> >> You can use MMC_CAP2_HSX00_1_8V in caps2.  
> > 
> > I can't quite follow you, how this should be used here?
> >   
> 
> Similar to 
> 
>         if (tegra_host->soc_data->nvquirks & NVQUIRK_ENABLE_DDR50)      
>                                                                    
>                 host->mmc->caps |= MMC_CAP_1_8V_DDR
> 
> You can enable higher speed eMMC modes without advertising SD card
> modes.

Makes sense. Thanks for clearing that up.

> >> So far the Tegra SDHCI driver did not use device tree to indicate modes,
> >> but maybe we should start doing that. In this case you can use
> >> mmc-hs200-1_8v/mmc-hs400-1_8v to indicate higher eMMC speed modes.
> >>  
> >> > +
> >> > +	/*
> >> > +	 * If the board does not define a regulator for the SDHCI IO voltage,
> >> > +	 * then don't advertise support for UHS modes even if the device
> >> > +	 * supports it because the IO voltage cannot be configured.
> >> > +	 */
> >> > +	if (IS_ERR(host->mmc->supply.vqmmc))
> >> > +		return false;  
> >>
> >> The stack should already check that and mask caps1 accordingly (see
> >> sdhci_setup_host).  
> > 
> > True, the logic seems to be duplicated here. Although also
> > tegra_sdhci_reset() needs to be change so that the bits masked off by
> > sdhci_setup_host() aren't set if this check is removed.
> >   
> 
> sdhci_setup_host() calls reset before doing initialization (e.g. in
> __sdhci_read_caps).
> 
> Checking just for vqmmc presence is bogus IMHO. It does not say anything
> about the exact capabilities of that regulator.

Yes, by itself it doesn't make much sense. It looks like the regulator
voltage checking code from sdhci_setup_host() has to be duplicated to
the tegra driver because the regulator checks are done after the reset
callback. The sdhci-tegra driver needs to make sure that the faster
signaling modes are enabled only if pinctrl properties are present on SD
controllers with variable voltage regulators.

> I think we should do something like this:
> 
> 	if (there is a host->mmc->supply.vqmmc) {
> 		if (host->mmc->supply.vqmmc can do 1.8V (or/and also 1.2V?)) {
> 			/* 
> 			 * Enable SDHCI spec v3.00 support
> 			 * This is required for SD UHS modes as well as higher eMMC speeds
> 			 */
> 			if (soc_data->nvquirks & NVQUIRK_ENABLE_SDHCI_SPEC_300)
> 				misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_SDHCI_SPEC_300;
> 
> 			if (host->mmc->supply.vqmmc can do 3.3V) {
> 				/*
> 				 * Proper SD voltage switching is possible, advertise SD UHS 
> 				 * modes as supported by host
> 				 */
> 				if (soc_data->nvquirks & NVQUIRK_ENABLE_SDR50)
> 					misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_SDR50;
> 				if (soc_data->nvquirks & NVQUIRK_ENABLE_DDR50)
> 					misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_DDR50;
> 				if (soc_data->nvquirks & NVQUIRK_ENABLE_SDR104)
> 					misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_SDR104;
> 				if (soc_data->nvquirks & SDHCI_MISC_CTRL_ENABLE_SDR50)
> 					clk_ctrl |= SDHCI_CLOCK_CTRL_SDR50_TUNING_OVERRIDE;
> 			}
> 		}
> 	}
> 
> 
> 
> 
> >> > +
> >> > +	/*
> >> > +	 * Later SoC generations require software pad voltage configuration.
> >> > +	 * The UHS modes should only be enabled if the pad configuration states
> >> > +	 * are available on platforms where they are required in order to switch
> >> > +	 * the signaling voltage.
> >> > +	 */
> >> > +	if (soc_data->nvquirks & NVQUIRK_NEEDS_PAD_CONTROL)
> >> > +		return tegra_host->pad_control_available;
> >> > +
> >> > +	return false;
> >> > +}
> >> > +
> >> >  static void tegra_sdhci_reset(struct sdhci_host *host, u8 mask)
> >> >  {
> >> >  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >> >  	struct sdhci_tegra *tegra_host = sdhci_pltfm_priv(pltfm_host);
> >> >  	const struct sdhci_tegra_soc_data *soc_data = tegra_host->soc_data;
> >> >  	u32 misc_ctrl, clk_ctrl;
> >> > +	bool uhs_valid;
> >> >
> >> >  	sdhci_reset(host, mask);
> >> >
> >> > @@ -160,13 +202,8 @@ static void tegra_sdhci_reset(struct sdhci_host
> >> > *host, u8 mask)
> >> >
> >> >  	clk_ctrl &= ~SDHCI_CLOCK_CTRL_SPI_MODE_CLKEN_OVERRIDE;
> >> >
> >> > -	/*
> >> > -	 * If the board does not define a regulator for the SDHCI
> >> > -	 * IO voltage, then don't advertise support for UHS modes
> >> > -	 * even if the device supports it because the IO voltage
> >> > -	 * cannot be configured.
> >> > -	 */
> >> > -	if (!IS_ERR(host->mmc->supply.vqmmc)) {
> >> > +	uhs_valid = tegra_sdhci_is_uhs_valid(host);
> >> > +	if (uhs_valid) {
> >> >  		/* Erratum: Enable SDHCI spec v3.00 support */
> >> >  		if (soc_data->nvquirks & NVQUIRK_ENABLE_SDHCI_SPEC_300)
> >> >  			misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_SDHCI_SPEC_300;
> >> > @@ -286,14 +323,80 @@ static int tegra_sdhci_execute_tuning(struct
> >> > sdhci_host *host, u32 opcode)
> >> >  	return mmc_send_tuning(host->mmc, opcode, NULL);
> >> >  }
> >> >
> >> > -static void tegra_sdhci_voltage_switch(struct sdhci_host *host)
> >> > +static int tegra_sdhci_set_padctrl(struct sdhci_host *host, int voltage)
> >> >  {
> >> >  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >> >  	struct sdhci_tegra *tegra_host = sdhci_pltfm_priv(pltfm_host);
> >> > -	const struct sdhci_tegra_soc_data *soc_data = tegra_host->soc_data;
> >> > +	int ret;
> >> > +
> >> > +	if (!tegra_host->pad_control_available)
> >> > +		return 0;
> >> > +
> >> > +	if (voltage == MMC_SIGNAL_VOLTAGE_180) {
> >> > +		ret = pinctrl_select_state(tegra_host->pinctrl_sdmmc,
> >> > +					   tegra_host->pinctrl_state_1v8);
> >> > +		if (ret < 0)
> >> > +			dev_err(mmc_dev(host->mmc),
> >> > +				"setting 1.8V failed, ret: %d\n", ret);
> >> > +	} else {
> >> > +		ret = pinctrl_select_state(tegra_host->pinctrl_sdmmc,
> >> > +					   tegra_host->pinctrl_state_3v3);
> >> > +		if (ret < 0)
> >> > +			dev_err(mmc_dev(host->mmc),
> >> > +				"setting 3.3V failed, ret: %d\n", ret);
> >> > +	}
> >> >
> >> > -	if (soc_data->nvquirks & NVQUIRK_HAS_PADCALIB)
> >> > -		tegra_host->pad_calib_required = true;  
> 
> Is this really not needed anymore?

Good catch. That probably happened accidentally during a rebase.

> >> > +	return ret;
> >> > +}
> >> > +
> >> > +static int sdhci_tegra_start_signal_voltage_switch(struct mmc_host *mmc,
> >> > +						   struct mmc_ios *ios)
> >> > +{
> >> > +	struct sdhci_host *host = mmc_priv(mmc);
> >> > +	int ret = 0;
> >> > +
> >> > +	if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_330) {
> >> > +		ret = tegra_sdhci_set_padctrl(host, ios->signal_voltage);
> >> > +		if (ret < 0)
> >> > +			return ret;
> >> > +		ret = sdhci_start_signal_voltage_switch(mmc, ios);
> >> > +	} else if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_180) {
> >> > +		ret = sdhci_start_signal_voltage_switch(mmc, ios);
> >> > +		if (ret < 0)
> >> > +			return ret;
> >> > +		ret = tegra_sdhci_set_padctrl(host, ios->signal_voltage);  
> >>
> >> So depending on voltage you first set the pads setting and then do the
> >> signaling voltage switch. Is this necessary? Why?  
> > 
> > This is done to enforce the constraint of keeping the signaling voltage
> > always less or equal to the pad voltage. Driving 3.3 V into a pad that
> > has been configured to 1.8 V will damage it. This is stated in the
> > Tegra210 and Tegra186 TRMs in SDMMC Initialization Sequece sections of
> > controllers supporting voltage switching.
> > 
> > Here when switching from 3.3 V to 1.8 V the regulator is first
> > configured to 1.8 V by sdhci_start_signal_voltage_switch() and after
> > that the pad is configured to 1.8 V. When going in the other direction
> > the pad needs to be first configured to 3.3 V before the regulator
> > voltage can be raised.  
> 
> Ok makes sense. Can you add a comment, e.g. /* Order of operation
> matters, it make sure to keep signaling voltage below pad voltage */
> 
> >   
> >> > +	}
> >> > +
> >> > +	return ret;
> >> > +}
> >> > +
> >> > +static void tegra_sdhci_init_pinctrl_info(struct device *dev,
> >> > +					  struct sdhci_tegra *tegra_host)
> >> > +{
> >> > +	tegra_host->pinctrl_sdmmc = devm_pinctrl_get(dev);
> >> > +	if (IS_ERR(tegra_host->pinctrl_sdmmc)) {
> >> > +		dev_dbg(dev, "No pinctrl info, err: %ld\n",
> >> > +			PTR_ERR(tegra_host->pinctrl_sdmmc));
> >> > +		return;
> >> > +	}
> >> > +
> >> > +	tegra_host->pinctrl_state_3v3 =
> >> > +		pinctrl_lookup_state(tegra_host->pinctrl_sdmmc, "sdmmc-3v3");
> >> > +	if (IS_ERR(tegra_host->pinctrl_state_3v3)) {
> >> > +		dev_err(dev, "Missing 3.3V pad state, err: %ld\n",
> >> > +			PTR_ERR(tegra_host->pinctrl_state_3v3));
> >> > +		return;
> >> > +	}
> >> > +
> >> > +	tegra_host->pinctrl_state_1v8 =
> >> > +		pinctrl_lookup_state(tegra_host->pinctrl_sdmmc, "sdmmc-1v8");
> >> > +	if (IS_ERR(tegra_host->pinctrl_state_1v8)) {
> >> > +		dev_err(dev, "Missing 1.8V pad state, err: %ld\n",
> >> > +			  PTR_ERR(tegra_host->pinctrl_state_3v3));  
> >>
> >> Is missing pad states considered as error? If yes, we should return a
> >> error code and make the probe function fail.
> >>
> >> If it is ok to run it without the states, then this should be dev_warn
> >> or dev_info.  
> > 
> > I don't think failing probe due to missing pinctrl entries can be done
> > because it would break backwards compatibility with pre-existing dtbs.
> > Also SDHCI controllers with fixed signaling voltage don't support pad
> > voltage reconfiguration and therefore the pinctrl properties won't be
> > there either. In the case of fixed voltage SDHCI controllers the
> > "nvidia,only-1-8-v" property is used to signal that pad reconfiguration
> > doesn't need to be performed.  
> 
> Ok, if they are not mandatory, just use dev_warn(...).
> 
> Btw,
> 
> +    if (soc_data->nvquirks & NVQUIRK_NEEDS_PAD_CONTROL) {
> +        host->mmc_host_ops.start_signal_voltage_switch =
> +            sdhci_tegra_start_signal_voltage_switch;
> +        tegra_sdhci_init_pinctrl_info(&pdev->dev, tegra_host);
> +    }
> +
> 
> Can we make tegra_sdhci_init_pinctrl_info return a boolean and do the
> tegra_host->pad_control_available assignment here? I think this would be
> cleaner.
> 
> It also won't assign host->mmc_host_ops.start_signal_voltage_switch if
> not needed.
> 
> 	if (soc_data->nvquirks & NVQUIRK_NEEDS_PAD_CONTROL &&
> 	    tegra_sdhci_init_pinctrl_info(&pdev->dev, tegra_host)) {
> 		host->mmc_host_ops.start_signal_voltage_switch =
> 			sdhci_tegra_start_signal_voltage_switch;
> 		tegra_host->pad_control_available = true;
> 	}

 -Aapo

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