RE: [PATCH v4 4/4] mmc: sdhci-of-arasan: Enable UHS-1 support for Keem Bay SOC

["Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@intel.com>]

Hi Ulf,

I am following up for below comments and would be grateful for your prompt reply.
Thanks

>-----Original Message-----
>From: Zulkifli, Muhammad Husaini
>Sent: Saturday, October 10, 2020 1:50 AM
>To: Ulf Hansson <ulf.hansson@linaro.org>
>Cc: Hunter, Adrian <adrian.hunter@intel.com>; Michal Simek
><michal.simek@xilinx.com>; Shevchenko, Andriy
><andriy.shevchenko@intel.com>; linux-mmc@vger.kernel.org; Linux ARM
><linux-arm-kernel@lists.infradead.org>; Linux Kernel Mailing List <linux-
>kernel@vger.kernel.org>; Raja Subramanian, Lakshmi Bai
><lakshmi.bai.raja.subramanian@intel.com>; Wan Mohamad, Wan Ahmad
>Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>; Arnd Bergmann
><arnd@arndb.de>
>Subject: RE: [PATCH v4 4/4] mmc: sdhci-of-arasan: Enable UHS-1 support for
>Keem Bay SOC
>
>Hi,
>
>>-----Original Message-----
>>From: Ulf Hansson <ulf.hansson@linaro.org>
>>Sent: Friday, October 9, 2020 2:56 PM
>>To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@intel.com>
>>Cc: Hunter, Adrian <adrian.hunter@intel.com>; Michal Simek
>><michal.simek@xilinx.com>; Shevchenko, Andriy
>><andriy.shevchenko@intel.com>; linux-mmc@vger.kernel.org; Linux ARM
>><linux-arm-kernel@lists.infradead.org>; Linux Kernel Mailing List
>><linux- kernel@vger.kernel.org>; Raja Subramanian, Lakshmi Bai
>><lakshmi.bai.raja.subramanian@intel.com>; Wan Mohamad, Wan Ahmad
>Zainie
>><wan.ahmad.zainie.wan.mohamad@intel.com>; Arnd Bergmann
><arnd@arndb.de>
>>Subject: Re: [PATCH v4 4/4] mmc: sdhci-of-arasan: Enable UHS-1 support
>>for Keem Bay SOC
>>
>>On Thu, 8 Oct 2020 at 19:21, Zulkifli, Muhammad Husaini
>><muhammad.husaini.zulkifli@intel.com> wrote:
>>>
>>> Hi,
>>>
>>> >-----Original Message-----
>>> >From: Ulf Hansson <ulf.hansson@linaro.org>
>>> >Sent: Thursday, October 8, 2020 11:19 PM
>>> >To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@intel.com>
>>> >Cc: Hunter, Adrian <adrian.hunter@intel.com>; Michal Simek
>>> ><michal.simek@xilinx.com>; Shevchenko, Andriy
>>> ><andriy.shevchenko@intel.com>; linux-mmc@vger.kernel.org; Linux ARM
>>> ><linux-arm-kernel@lists.infradead.org>; Linux Kernel Mailing List
>>> ><linux- kernel@vger.kernel.org>; Raja Subramanian, Lakshmi Bai
>>> ><lakshmi.bai.raja.subramanian@intel.com>; Wan Mohamad, Wan Ahmad
>>> >Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>; Arnd Bergmann
>>> ><arnd@arndb.de>
>>> >Subject: Re: [PATCH v4 4/4] mmc: sdhci-of-arasan: Enable UHS-1
>>> >support for Keem Bay SOC
>>> >
>>> >On Thu, 8 Oct 2020 at 12:54, Zulkifli, Muhammad Husaini
>>> ><muhammad.husaini.zulkifli@intel.com> wrote:
>>> >>
>>> >> Hi,
>>> >>
>>> >> >-----Original Message-----
>>> >> >From: Ulf Hansson <ulf.hansson@linaro.org>
>>> >> >Sent: Thursday, October 8, 2020 5:28 PM
>>> >> >To: Zulkifli, Muhammad Husaini
>>> >> ><muhammad.husaini.zulkifli@intel.com>
>>> >> >Cc: Hunter, Adrian <adrian.hunter@intel.com>; Michal Simek
>>> >> ><michal.simek@xilinx.com>; Shevchenko, Andriy
>>> >> ><andriy.shevchenko@intel.com>; linux-mmc@vger.kernel.org; Linux
>>> >> >ARM <linux-arm-kernel@lists.infradead.org>; Linux Kernel Mailing
>>> >> >List
>>> >> ><linux- kernel@vger.kernel.org>; Raja Subramanian, Lakshmi Bai
>>> >> ><lakshmi.bai.raja.subramanian@intel.com>; Wan Mohamad, Wan
>>Ahmad
>>> >> >Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>; Arnd Bergmann
>>> >> ><arnd@arndb.de>
>>> >> >Subject: Re: [PATCH v4 4/4] mmc: sdhci-of-arasan: Enable UHS-1
>>> >> >support for Keem Bay SOC
>>> >> >
>>> >> >On Thu, 8 Oct 2020 at 04:12,
>>> >> ><muhammad.husaini.zulkifli@intel.com>
>>> >wrote:
>>> >> >>
>>> >> >> From: Muhammad Husaini Zulkifli
>>> >> >> <muhammad.husaini.zulkifli@intel.com>
>>> >> >>
>>> >> >> Voltage switching sequence is needed to support UHS-1 interface.
>>> >> >> There are 2 places to control the voltage.
>>> >> >> 1) By setting the AON register using firmware driver calling
>>> >> >> system-level platform management layer (SMC) to set the register.
>>> >> >> 2) By controlling the GPIO expander value to drive either 1.8V
>>> >> >> or 3.3V for power mux input.
>>> >> >>
>>> >> >> Signed-off-by: Muhammad Husaini Zulkifli
>>> >> >> <muhammad.husaini.zulkifli@intel.com>
>>> >> >> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
>>> >> >> Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
>>> >> >> ---
>>> >> >>  drivers/mmc/host/sdhci-of-arasan.c | 126
>>> >> >> +++++++++++++++++++++++++++++
>>> >> >>  1 file changed, 126 insertions(+)
>>> >> >>
>>> >> >> diff --git a/drivers/mmc/host/sdhci-of-arasan.c
>>> >> >> b/drivers/mmc/host/sdhci-of-arasan.c
>>> >> >> index 46aea6516133..ea2467b0073d 100644
>>> >> >> --- a/drivers/mmc/host/sdhci-of-arasan.c
>>> >> >> +++ b/drivers/mmc/host/sdhci-of-arasan.c
>>> >> >> @@ -16,6 +16,7 @@
>>> >> >>   */
>>> >> >>
>>> >> >>  #include <linux/clk-provider.h>
>>> >> >> +#include <linux/gpio/consumer.h>
>>> >> >>  #include <linux/mfd/syscon.h>
>>> >> >>  #include <linux/module.h>
>>> >> >>  #include <linux/of_device.h>
>>> >> >> @@ -23,6 +24,7 @@
>>> >> >>  #include <linux/regmap.h>
>>> >> >>  #include <linux/of.h>
>>> >> >>  #include <linux/firmware/xlnx-zynqmp.h>
>>> >> >> +#include <linux/firmware/intel/keembay_firmware.h>
>>> >> >>
>>> >> >>  #include "cqhci.h"
>>> >> >>  #include "sdhci-pltfm.h"
>>> >> >> @@ -136,6 +138,7 @@ struct sdhci_arasan_clk_data {
>>> >> >>   * @soc_ctl_base:      Pointer to regmap for syscon for soc_ctl registers.
>>> >> >>   * @soc_ctl_map:       Map to get offsets into soc_ctl registers.
>>> >> >>   * @quirks:            Arasan deviations from spec.
>>> >> >> + * @uhs_gpio:          Pointer to the uhs gpio.
>>> >> >>   */
>>> >> >>  struct sdhci_arasan_data {
>>> >> >>         struct sdhci_host *host; @@ -150,6 +153,7 @@ struct
>>> >> >> sdhci_arasan_data {
>>> >> >>         struct regmap   *soc_ctl_base;
>>> >> >>         const struct sdhci_arasan_soc_ctl_map *soc_ctl_map;
>>> >> >>         unsigned int    quirks;
>>> >> >> +       struct gpio_desc *uhs_gpio;
>>> >> >>
>>> >> >>  /* Controller does not have CD wired and will not function
>>> >> >> normally without
>>> >> >*/
>>> >> >>  #define SDHCI_ARASAN_QUIRK_FORCE_CDTEST        BIT(0)
>>> >> >> @@ -361,6 +365,112 @@ static int
>>> >> >> sdhci_arasan_voltage_switch(struct
>>> >> >mmc_host *mmc,
>>> >> >>         return -EINVAL;
>>> >> >>  }
>>> >> >>
>>> >> >> +static int sdhci_arasan_keembay_voltage_switch(struct mmc_host
>>> >*mmc,
>>> >> >> +                                      struct mmc_ios *ios) {
>>> >> >> +       struct sdhci_host *host = mmc_priv(mmc);
>>> >> >> +       struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>> >> >> +       struct sdhci_arasan_data *sdhci_arasan =
>>> >sdhci_pltfm_priv(pltfm_host);
>>> >> >> +       u16 ctrl_2, clk;
>>> >> >> +       int ret;
>>> >> >> +
>>> >> >> +       switch (ios->signal_voltage) {
>>> >> >> +       case MMC_SIGNAL_VOLTAGE_180:
>>> >> >> +               clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
>>> >> >> +               clk &= ~SDHCI_CLOCK_CARD_EN;
>>> >> >> +               sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
>>> >> >> +
>>> >> >> +               clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
>>> >> >> +               if (clk & SDHCI_CLOCK_CARD_EN)
>>> >> >> +                       return -EAGAIN;
>>> >> >> +
>>> >> >> +               sdhci_writeb(host, SDHCI_POWER_ON | SDHCI_POWER_180,
>>> >> >> +                                  SDHCI_POWER_CONTROL);
>>> >> >> +
>>> >> >> +               /*
>>> >> >> +                * Set VDDIO_B voltage to Low for 1.8V
>>> >> >> +                * which is controlling by GPIO Expander.
>>> >> >> +                */
>>> >> >> +
>>> >> >> + gpiod_set_value_cansleep(sdhci_arasan->uhs_gpio,
>>> >> >> + 0);
>>> >> >> +
>>> >> >> +               /*
>>> >> >> +                * This is like a final gatekeeper. Need to
>>> >> >> + ensure changed
>>> >voltage
>>> >> >> +                * is settled before and after turn on this bit.
>>> >> >> +                */
>>> >> >> +               usleep_range(1000, 1100);
>>> >> >> +
>>> >> >> +               ret =
>>> >keembay_sd_voltage_selection(KEEMBAY_SET_1V8_VOLT);
>>> >> >> +               if (ret)
>>> >> >> +                       return ret;
>>> >> >> +
>>> >> >> +               usleep_range(1000, 1100);
>>> >> >
>>> >> >No, sorry, but I don't like this.
>>> >> >
>>> >> >This looks like a GPIO regulator with an extension of using the
>>> >> >keembay_sd_voltage_selection() thingy. I think you can model
>>> >> >these things behind a regulator and hook it up as a vqmmc supply
>>> >> >in DT instead. BTW, this is the common way we deal with these
>>> >> >things for mmc
>>> >host drivers.
>>> >>
>>> >> The SDcard for Keem Bay SOC does not have its own voltage regulator.
>>> >> There are 2 places to control the voltage.
>>> >> 1) By setting the AON register calling system-level platform
>>> >> management
>>> >layer (SMC)
>>> >>    to set the I/O pads voltage for particular GPIOs line for clk,data and cmd.
>>> >>    The reason why I use this keembay_sd_voltage_selection() via
>>> >> smccc
>>> >interface it because during voltage switching
>>> >>    I need to access to AON register. On a secure system, we could
>>> >> not
>>> >directly access to AON register due to some security concern from
>>> >driver side, thus
>>> >>    cannot exposed any register or address.
>>> >> 2) By controlling the GPIO expander value to drive either 1.8V or
>>> >> 3.3V for
>>> >power mux input.
>>> >
>>> >I see, thanks for clarifying.
>>> >
>>> >To me, it sounds like the best fit is to implement a pinctrl (to
>>> >manage the I/O
>>> >pads) and a GPIO regulator.
>>> >
>>> Even with pinctrl, i still need to use the
>>> keembay_sd_voltage_selection()
>>thingy for AON register.
>>
>>Yes, I am fine by that.
>>
>>Although, as it's really a pinctrl, it deserves to be modelled like
>>that. Not as a soc specific hack in a mmc host driver.
>>
>>> Plus, the GPIO pin that control the sd-voltage is in GPIO Expander
>>> not using
>>Keembay SOC GPIO Pin.
>>> The best option is using the gpio consumer function to toggle the pin.
>>
>>As I said, please no.
>>
>>The common way to model this is as a GPIO regulator. In this way, you
>>can even rely on existing mmc DT bindings. All you have to do is to
>>hook up a vqmmc supply to the mmc node.
>>
>>To be clear, as long as there are no arguments for why a pinctrl and
>>GPIO regulator can't be used - I am not going to pick up the patches.
>As I mentioned The SDcard does not have its own voltage regulator.
>It only uses the voltage rails on the mux input.
>
>There are 2 things need to be configured before getting the output voltage:
>
>1) V_VDDIO_B :
>Supplied voltage applied to I/O Rail which is controlled from the Always on
>domain using specific bits in AON_CFG1 register.
>This is where we set for V_VDDIO_B using the keembay_sd_voltage_selection()
>to set either 1.8v or 3.3v depending on the bit value.
>IMHO, we do not pinctrl to do this.
>
>2) V_VDDIO_B_MAIN:
>The output V_VDDIO_B_MAIN (OUT1) will be either V_3P3_MAIN (IN1) or
>V_1P8_MAIN (IN2), depending on the state of GPIO expander Pin value. There is
>a POWER MUX involving here.
>IMHO, we do not need any gpio regulator/regulator api hook up for this.
>Most important thing, there is no regulator ic at all.
>We still need to manually control and toggle the pin value.
>
>The final IO voltage is set by V_VDDIO_B (= V_VDDIO_B_MAIN after passing
>through voltage sense resistor).
>
>Hope this will clarify.
>
>>
>>Kind regards
>>Uffe