Re: [RFC PATH 2/2] gpio: starfive-jh7100: Add StarFive JH7100 GPIO driver

From: Drew Fustini <drew@beagleboard.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Michael Walle <michael@walle.cc>,
	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
Date: Mon, 26 Jul 2021 00:11:24 -0700	[thread overview]
Message-ID: <20210726071124.GA9184@x1> (raw)
In-Reply-To: <CACRpkdbhKsuXZiLCh_iajJQWDdQQOZ87QF3xDr5Vc66SoVCnxQ@mail.gmail.com>

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.
> 
> 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].

Thus the input could work with gpio-mmio but I am not sure how to
reconcile the register-per-gpio for the output value and output enable.

Is there way a way to adapt gpio-mmio for this situation?

Thanks,
Drew

[1] https://github.com/starfive-tech/beaglev_doc

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