linux-kernel - Re: [PATCH v7 08/10] i2c: of-prober: Add GPIO support to simple helpers

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Message-ID: <ZuQZfvqGii9fcH-j@smile.fi.intel.com>
Date: Fri, 13 Sep 2024 13:52:46 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Wolfram Sang <wsa@...nel.org>, Benson Leung <bleung@...omium.org>,
	Tzung-Bi Shih <tzungbi@...nel.org>, Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Douglas Anderson <dianders@...omium.org>,
	Johan Hovold <johan@...nel.org>, Jiri Kosina <jikos@...nel.org>,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v7 08/10] i2c: of-prober: Add GPIO support to simple
 helpers

On Wed, Sep 11, 2024 at 03:27:46PM +0800, Chen-Yu Tsai wrote:
> Add GPIO support to the simple helpers for the I2C OF component prober.
> Components that the prober intends to probe likely require their
> regulator supplies be enabled, and GPIOs be toggled to enable them or
> bring them out of reset before they will respond to probe attempts.
> Regulator supplies were handled in the previous patch.
> 
> The assumption is that the same class of components to be probed are
> always connected in the same fashion with the same regulator supply
> and GPIO. The names may vary due to binding differences, but the
> physical layout does not change.
> 
> This supports at most one GPIO pin. The user must specify the GPIO name,
> the polarity, and the amount of time to wait after the GPIO is toggled.
> Devices with more than one GPIO pin likely require specific power
> sequencing beyond what generic code can easily support.

...

> +static int i2c_of_probe_simple_get_gpiod(struct device *dev, struct device_node *node,
> +					 struct i2c_of_probe_simple_ctx *ctx)
> +{
> +	struct fwnode_handle *fwnode = of_fwnode_handle(node);
> +	struct gpio_desc *gpiod;
> +	const char *con_id = NULL;
> +
> +	/* NULL signals no GPIO needed */
> +	if (!ctx->opts->gpio_name)
> +		return 0;
> +
> +	/* An empty string signals an unnamed GPIO */
> +	if (strlen(ctx->opts->gpio_name))

You run for entire string in order to check the first byte only?

	if (ctx->opts->gpio_name[0] == '\0')
		con_id = NULL;
	else

> +		con_id = ctx->opts->gpio_name;

Also note, that comment is given in inverted condition to what you actually do
in the code. With my suggestion it looks better.

> +	gpiod = fwnode_gpiod_get_index(fwnode, con_id, 0, GPIOD_ASIS, "i2c-of-prober");
> +	if (IS_ERR(gpiod))
> +		return PTR_ERR(gpiod);
> +
> +	ctx->gpiod = gpiod;
> +
> +	return 0;
> +}

...

> +static int i2c_of_probe_simple_set_gpio(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
> +{
> +	int ret;
> +
> +	if (!ctx->gpiod)
> +		return 0;

> +	dev_dbg(dev, "Setting GPIO\n");

> +	ret = gpiod_direction_output_raw(ctx->gpiod, ctx->opts->gpio_high_to_enable ? 1 : 0);

Hmm... _raw() in use... Perhaps it's on a territory of Bart and Linus to review
and comment on this.

> +	if (ret)
> +		return ret;
> +
> +	msleep(ctx->opts->post_reset_deassert_delay_ms);
> +
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko