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Subject[PATCH 2/3 v3] dt-bindings: gpio: aspeed: Add SGPIO support
Date
Add bindings to support SGPIO on AST2400 or AST2500.

Signed-off-by: Hongwei Zhang <hongweiz@ami.com>
---
.../devicetree/bindings/gpio/sgpio-aspeed.txt | 55 ++++++++++++++++++++++
1 file changed, 55 insertions(+)
create mode 100644 Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt

diff --git a/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt b/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
new file mode 100644
index 0000000..8c3a747
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
@@ -0,0 +1,55 @@
+Aspeed SGPIO controller Device Tree Bindings
+-------------------------------------------
+
+This SGPIO controller is for ASPEED AST2500 SoC, it supports up to 80 full
+featured Serial GPIOs. Each of the Serial GPIO pins can be programmed to
+support the following options:
+- Support interrupt option for each input port and various interrupt
+ sensitivity option (level-high, level-low, edge-high, edge-low)
+- Support reset tolerance option for each output port
+- Directly connected to APB bus and its shift clock is from APB bus clock
+ divided by a programmable value.
+- Co-work with external signal-chained TTL components (74LV165/74LV595)
+
+
+Required properties:
+
+- compatible : Either "aspeed,ast2400-sgpio" or "aspeed,ast2500-sgpio"
+
+- #gpio-cells : Should be two
+ - First cell is the GPIO line number
+ - Second cell is used to specify optional
+ parameters (unused)
+
+- reg : Address and length of the register set for the device
+- gpio-controller : Marks the device node as a GPIO controller.
+- interrupts : Interrupt specifier (see interrupt bindings for
+ details)
+
+- interrupt-controller : Mark the GPIO controller as an interrupt-controller
+
+- nr-gpios : number of GPIO pins to serialise.
+ (should be multiple of 8, up to 80 pins; 0 if not used)
+
+- clocks : A phandle to the APB clock for SGPM clock division
+
+- bus-frequency : SGPM CLK frequency, derived from APB bus clock by a programmable devisor
+
+
+The sgpio and interrupt properties are further described in their respective bindings documentation:
+
+- Documentation/devicetree/bindings/sgpio/gpio.txt
+- Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+
+ Example:
+ sgpio@1e780200 {
+ #gpio-cells = <2>;
+ compatible = "aspeed,ast2500-sgpio";
+ gpio-controller;
+ interrupts = <40>;
+ reg = <0x1e780200 0x0100>;
+ clocks = <&syscon ASPEED_CLK_APB>;
+ interrupt-controller;
+ nr-gpios = <8>;
+ bus-frequency = <12000000>;
+ };
--
2.7.4

Thanks Andrew, please see above v3 and inline comments at below.
--Hongwei

> From: Andrew Jeffery <andrew@aj.id.au>
> Sent: Sunday, July 14, 2019 10:25 PM
> To: Hongwei Zhang; Joel Stanley; Linus Walleij; devicetree@vger.kernel.org
> Cc: Rob Herring; Mark Rutland; Bartosz Golaszewski; linux-aspeed@lists.ozlabs.org; linux-
> kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-gpio@vger.kernel.org
> Subject: Re: [PATCH 2/3 v2] dt-bindings: gpio: aspeed: Add SGPIO support
>
> Hello Hongwei,
>
> On Sat, 13 Jul 2019, at 05:44, Hongwei Zhang wrote:
> > Add bindings to support SGPIO on AST2400 or AST2500.
> >
> > Signed-off-by: Hongwei Zhang <hongweiz@ami.com>
> > ---
> > .../devicetree/bindings/gpio/sgpio-aspeed.txt | 43 ++++++++++++++++++++++
> > 1 file changed, 43 insertions(+)
> > create mode 100755
> > Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
> >
> > diff --git a/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
> > b/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
> > new file mode 100755
> > index 0000000..3ae2b79
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/gpio/sgpio-aspeed.txt
> > @@ -0,0 +1,43 @@
> > +Aspeed SGPIO controller Device Tree Bindings
> > +-------------------------------------------
> > +
> > +Required properties:
> > +- compatible : Either "aspeed,ast2400-sgpio" or "aspeed,ast2500-sgpio"
> > +
> > +- #gpio-cells : Should be two
> > + - First cell is the GPIO line number
> > + - Second cell is used to specify optional
> > + parameters (unused)
> > +
> > +- reg : Address and length of the register set for the device
> > +- gpio-controller : Marks the device node as a GPIO controller.
> > +- interrupts : Interrupt specifier (see interrupt bindings for
> > + details)
> > +
> > +- interrupt-controller : Mark the GPIO controller as an
> > interrupt-controller
> > +
> > +- nr-gpios : number of GPIO pins to serialise. (should be multiple of
> > 8, up to 80 pins)
> > + if not specified, defaults to 80.
>
> This appears to be a statement about the driver implementation, but bindings documents are about
> describing hardware. Reading the datasheet it actually appears the ASPEED SGPIO hardware comes up
> in what is "technically" a forbidden state (equivalent to `nr-gpios = <0>;`), though the device is also
> disabled at this point, so it's probably moot. The point is the true default value from a hardware
> perspective is 0, not 80, so if we're going to talk about default values, 0 would be more appropriate.
> However:
>
> You've also listed nr-gpios under the "Required properties" header, but the description suggests it's
> optional. It's either one or the other, please lets be clear about it. On that front, lets make it nr-gpios
> *not* optional (i.e. make it
> required) thus force the specification of how many SGPIOs we want to emit on the bus. This value is
> coupled to the platform design, so I don't think there's ever a scenario where we want nr-gpios to take a
> default value.
>

Added some descriptions and updated nr-gpios, please see v3.

> > +
> > +- clocks : A phandle to the APB clock for SGPM clock
> > division
> > +
> > +- bus-frequency : SGPM CLK frequency, if not specified defaults to 1
> > MHz
>
> Again here with the default value - SGPM CLK period is derived from PCLK by the expression `period =
> PCLK * 2 *(GPIO254[31:16] + 1)`, where GPIO254's initialisation state is `GPIO254[31:16] = 0`, which
> gives a default SGPM bus frequency of PCLK / 2. This is likely not going to be 1MHz (more like ~12MHz).
>
> Lets just make the property required. That way we avoid any ambiguity about the bus frequency and
> thus don't need words about defaults that turn out to be about the driver, not about the hardware.
>

updated, please see v3.

> Finally, when updating patches in response to feedback, please send the full series again, and bump the
> series version number. That way people can review a coherent set of patches and not have to hunt
> around and (fail to) collate the correct combination. It makes it easier to say "Reviewed-by:" on your
> patches :)
>
> Cheers,
>
> Andrew

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