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

From: Ulf Hansson
Date: Thu Oct 08 2020 - 11:19:58 EST

On Thu, 8 Oct 2020 at 12:54, Zulkifli, Muhammad Husaini
<muhammad.husaini.zulkifli@xxxxxxxxx> wrote:
>
> Hi,
>
> >-----Original Message-----
> >From: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> >Sent: Thursday, October 8, 2020 5:28 PM
> >To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@xxxxxxxxx>
> >Cc: Hunter, Adrian <adrian.hunter@xxxxxxxxx>; Michal Simek
> ><michal.simek@xxxxxxxxxx>; Shevchenko, Andriy
> ><andriy.shevchenko@xxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx; Linux ARM
> ><linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; Linux Kernel Mailing List <linux-
> >kernel@xxxxxxxxxxxxxxx>; Raja Subramanian, Lakshmi Bai
> ><lakshmi.bai.raja.subramanian@xxxxxxxxx>; Wan Mohamad, Wan Ahmad
> >Zainie <wan.ahmad.zainie.wan.mohamad@xxxxxxxxx>; Arnd Bergmann
> ><arnd@xxxxxxxx>
> >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@xxxxxxxxx> wrote:
> >>
> >> From: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@xxxxxxxxx>
> >>
> >> 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@xxxxxxxxx>
> >> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> >> Reviewed-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> >> ---
> >> 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.

Kind regards
Uffe