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Date:   Mon, 26 Jul 2021 22:28:51 -0700
From:   Drew Fustini <drew@beagleboard.org>
To:     Michael Walle <michael@walle.cc>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Michael Zhu <michael.zhu@starfivetech.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Fu Wei <tekkamanninja@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Huan Feng <huan.feng@starfivetech.com>
Subject: Re: [RFC PATH 2/2] gpio: starfive-jh7100: Add StarFive JH7100 GPIO
 driver
Message-ID: <20210727052851.GA3147871@x1>
References: <20210701002037.912625-1-drew@beagleboard.org>
 <20210701002037.912625-3-drew@beagleboard.org>
 <8c59105d32a9936f8806501ecd20e044@walle.cc>
 <CACRpkdbhKsuXZiLCh_iajJQWDdQQOZ87QF3xDr5Vc66SoVCnxQ@mail.gmail.com>
 <20210726071124.GA9184@x1>
 <dad13b899b69436acc1804b7c3438639@walle.cc>
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On Mon, Jul 26, 2021 at 09:21:31AM +0200, Michael Walle wrote:
> Hi Drew, Hi Linus,
> 
> Am 2021-07-26 09:11, schrieb Drew Fustini:
> > On Fri, Jul 23, 2021 at 11:04:41PM +0200, Linus Walleij wrote:
> > > On Thu, Jul 1, 2021 at 8:39 AM Michael Walle <michael@walle.cc> wrote:
> > > > Am 2021-07-01 02:20, schrieb Drew Fustini:
> > > > > Add GPIO driver for the StarFive JH7100 SoC [1] used on the
> > > > > BeagleV Starlight JH7100 board [2].
> > > > >
> > > > > [1] https://github.com/starfive-tech/beaglev_doc/
> > > > > [2] https://github.com/beagleboard/beaglev-starlight
> > > > >
> > > > > Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
> > > > > Signed-off-by: Huan Feng <huan.feng@starfivetech.com>
> > > > > Signed-off-by: Drew Fustini <drew@beagleboard.org>
> > > >
> > > > Could this driver use GPIO_REGMAP and REGMAP_IRQ? See
> > > > drivers/gpio/gpio-sl28cpld.c for an example.
> > > 
> > > To me it looks just memory-mapped?
> > > 
> > > Good old gpio-mmio.c (select GPIO_GENERIC) should
> > > suffice I think.
> 
> But that doesn't mean gpio-regmap can't be used, no? Or what are
> the advantages of gpio-mmio?
> 
> > > Drew please look at drivers/gpio/gpio-ftgpio010.c for an example
> > > of GPIO_GENERIC calling bgpio_init() in probe().
> > 
> > Thank you for the suggestion. However, I am not sure that will work for
> > this SoC.
> > 
> > The GPIO registers are described in section 12 of JH7100 datasheet [1]
> > and I don't think they fit the expectation of gpio-mmio.c because there
> > is a seperate register for each GPIO line for output data value and
> > output enable.
> > 
> > There are 64 output data config registers which are 4 bytes wide. There
> > are 64 output enable config registers which are 4 bytes wide too. Output
> > data and output enable registers for a given GPIO pad are contiguous.
> > GPIO0_DOUT_CFG is 0x50 and GPIO0_DOEN_CFG is 0x54 while GPIO1_DOUT_CFG
> > is 0x58 and GPIO1_DOEN_CFG is 0x5C. The stride between GPIO pads is
> > effectively 8, which yields the formula: GPIOn_DOUT_CFG is 0x50+8n.
> > Similarly, GPIO0_DOEN_CFG is 0x54 and thus GPIOn_DOEN_CFG is 0x54+8n.
> > 
> > However, GPIO input data does use just one bit for each line. GPIODIN_0
> > at 0x48 covers GPIO[31:0] and GPIODIN_1 at 0x4c covers GPIO[63:32].
> 
> I'd say, that should work with the .reg_mask_xlate of the gpio-regmap.
> 
> -michael

Thanks, yes, I think trying to figure out how .reg_mask_xlate would need
to work this SoC.  I believe these are the only two implementations.

From drivers/gpio/gpio-regmap.c:

  static int gpio_regmap_simple_xlate(struct gpio_regmap *gpio,
				      unsigned int base, unsigned int offset,
				      unsigned int *reg, unsigned int *mask)
  {
	  unsigned int line = offset % gpio->ngpio_per_reg;
	  unsigned int stride = offset / gpio->ngpio_per_reg;

	  *reg = base + stride * gpio->reg_stride;
	  *mask = BIT(line);

	  return 0;
  }

From drivers/pinctrl/bcm/pinctrl-bcm63xx.c:

  static int bcm63xx_reg_mask_xlate(struct gpio_regmap *gpio,
				    unsigned int base, unsigned int offset,
				    unsigned int *reg, unsigned int *mask)
  {
	  unsigned int line = offset % BCM63XX_BANK_GPIOS;
	  unsigned int stride = offset / BCM63XX_BANK_GPIOS;

	  *reg = base - stride * BCM63XX_BANK_SIZE;
	  *mask = BIT(line);

	  return 0;
  }

Let's say a driver calls gpio_regmap_set(chip, 0, 5) to set line 5 to
value 1.

I believe this would result in call to:

  gpio->reg_mask_xlate(gpio, gpio->reg_set_base, 5, &reg, &mask)

Then this would be called to set the register:

  regmap_update_bits(gpio->regmap, reg, mask, mask);

From datasheet section 12 [1], there are 64 output data registers which
are 4 bytes wide. There are 64 output enable registers which are also 4
bytes wide too. Output data and output enable registers for a GPIO line
are contiguous. Thus GPIO0_DOUT_CFG is 0x50 and GPIO0_DOEN_CFG is 0x54.
The forumla is GPIOn_DOUT_CFG is 0x50+8n and GPIOn_DOEN_CFG is 0x54+8n.
Thus for GPIO line 5:

  GPIO5_DOUT_CFG is 0x50 + 0x28 = 0x78
  GPIO5_DOEN_CFG is 0x54 + 0x28 = 0x7C

Enable GPIO line 5 as output by writing 0x1 to 0x7C and set output value
to 1 by writing 1 to 0x7C.

Using gpio_regmap_simple_xlate() as a template, I am thinking through
xlate for this gpio controller:


static int gpio_regmap_starfive_xlate(struct gpio_regmap *gpio,
				      unsigned int base, unsigned int offset,
				      unsigned int *reg, unsigned int *mask)
{
	// reg_set_base is passed as base
	// let reg_set_base = 0x50 (GPIO0_DOUT_CFG)
	// let gpio->reg_stride = 8
	// let offest = 5 (for gpio line 5)

	*reg = base + offset * gpio->reg_stride;
	// *reg = base:0x50 + offset:0x5 * reg_stride:0x8
	// *reg = 0x50 + 0x28
	// *reg=  0x78

	// Each gpio line has a full register, not just a bit. To output
	// a digital 1, then GPIO5_DOUT_CFG would be 0x1. To output
	// digital 0, GPIO5_DOUT_CFG would be 0x0. Thus I think the mask
	// should be the least significant bit.
	*mask = BIT(1);

	return 0;
}

Let's walk through what would happen if gpio_regmap_set() was the
caller:

static void gpio_regmap_set(struct gpio_chip *chip, unsigned int offset,
			    int val)
{
	// for gpio line, offset = 5
	// if want to set line 5 high, then val = 1
	struct gpio_regmap *gpio = gpiochip_get_data(chip);

	// reg_set_base would be set to 0x50 (GPIO0_DOUT_CFG)
	unsigned int base = gpio_regmap_addr(gpio->reg_set_base);
	unsigned int reg, mask;

	gpio->reg_mask_xlate(gpio, base /* 0x50 */, offset /* 5 */, &reg, &mask);
	if (val) /* if val is 1 */
		regmap_update_bits(gpio->regmap, reg, mask, mask);
		// if mask returned was 0x1, then this would set the
		// bit 0 in GPIO5_DOUT_CFG
	else /* if val is 0 */
		regmap_update_bits(gpio->regmap, reg, mask, 0);
		// if mask returned was 0x1, then this would clear
		// bit 0 in GPIO5_DOUT_CFG
}

Now for the output enable register GPIO5_DOEN_CFG, the output driver is
active low so 0x0 is actually enables output where as 0x1 disables
output.  Thus maybe I need to add logic like:


static int gpio_regmap_starfive_xlate(struct gpio_regmap *gpio,
				      unsigned int base, unsigned int offset,
				      unsigned int *reg, unsigned int *mask)
{
	<snip>
	if (base == GPIO0_DOUT_CFG)
		*mask = 0x1U;
	else if (base == GPIO0_DOEN_CFG)
		*bit = ~(0x1U);

	return 0;
}

What do you think of that approach?

Are there any other examples of regmap xlate that I missed?

Thanks,
Drew

[1] https://github.com/starfive-tech/beaglev_doc/blob/main/JH7100%20Data%20Sheet%20V01.01.04-EN%20(4-21-2021).pdf