Re: [PATCH V3 3/3] gpio: modepin: Add driver support for modepin GPIO controller

From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Piyush Mehta <piyush.mehta@xilinx.com>,
	arnd@arndb.de, zou_wei@huawei.com, gregkh@linuxfoundation.org,
	linus.walleij@linaro.org, michal.simek@xilinx.com,
	wendy.liang@xilinx.com, iwamatsu@nigauri.org,
	bgolaszewski@baylibre.com, robh+dt@kernel.org,
	rajan.vaja@xilinx.com
Cc: linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
	git@xilinx.com, sgoud@xilinx.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Pengutronix Kernel Team <kernel@pengutronix.de>
Subject: Re: [PATCH V3 3/3] gpio: modepin: Add driver support for modepin GPIO controller
Date: Wed, 18 Aug 2021 10:52:02 +0200	[thread overview]
Message-ID: <b3d718af-6eb7-a212-f599-d0d91273afdc@pengutronix.de> (raw)
In-Reply-To: <20210818081018.2620544-4-piyush.mehta@xilinx.com>

On 18.08.21 10:10, Piyush Mehta wrote:
> This patch adds driver support for the zynqmp modepin GPIO controller.
> GPIO modepin driver set and get the value and status of the PS_MODE pin,
> based on device-tree pin configuration. These four mode pins are
> configurable as input/output. The mode pin has a control register, which
> have lower four-bits [0:3] are configurable as input/output, next four-bits
> can be used for reading the data  as input[4:7], and next setting the
> output pin state output[8:11].
> 
> Signed-off-by: Piyush Mehta <piyush.mehta@xilinx.com>
> Acked-by: Michal Simek <michal.simek@xilinx.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> ---

> +/**
> + * modepin_gpio_dir_in - Set the direction of the specified GPIO pin as input
> + * @chip:	gpio_chip instance to be worked on
> + * @pin:	gpio pin number within the device
> + *
> + * Return: 0 always
> + */
> +static int modepin_gpio_dir_in(struct gpio_chip *chip, unsigned int pin)
> +{
> +	return 0;
> +}

You say the gpio controller can configure pins as inputs or outputs.
Yet, .direction_input is doing nothing. So it's not clear to me,
how this sequence could work:

 - set gpio output high (writes bootmode)
 - set gpio to input (no-op, pin will remain high, not high impedance)

I didn't check the previous discussions, but if this indeed works as intended,
the how should be written here into the driver. That is a more useful comment
than kernel doc for a stub function.

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