linux-kernel - Re: [PATCH v5 08/10] i2c: of-prober: Add GPIO support

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Message-ID: <ZsdJOUe44hiGur-s@smile.fi.intel.com>
Date: Thu, 22 Aug 2024 17:20:41 +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 v5 08/10] i2c: of-prober: Add GPIO support

On Thu, Aug 22, 2024 at 05:20:01PM +0800, Chen-Yu Tsai wrote:
> This adds GPIO management to 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 support was added in the previous patch.
> 
> Without specific knowledge of each component's resource names or
> power sequencing requirements, the prober can only enable the
> regulator supplies all at once, and toggle the GPIOs all at once.
> Luckily, reset pins tend to be active low, while enable pins tend to
> be active high, so setting the raw status of all GPIO pins to high
> should work. The wait time before and after resources are enabled
> are collected from existing drivers and device trees.
> 
> The prober collects resources from all possible components and enables
> them together, instead of enabling resources and probing each component
> one by one. The latter approach does not provide any boot time benefits
> over simply enabling each component and letting each driver probe
> sequentially.
> 
> The prober will also deduplicate the resources, since on a component
> swap out or co-layout design, the resources are always the same.
> While duplicate regulator supplies won't cause much issue, shared
> GPIOs don't work reliably, especially with other drivers. For the
> same reason, the prober will release the GPIOs before the successfully
> probed component is actually enabled.

...

> +	struct fwnode_handle *fwnode = of_fwnode_handle(node);
> +	struct gpio_descs *gpiods;
> +	struct gpio_desc *gpiod;
> +	char con[32]; /* 32 is max size of property name */

Use 'propname' to be aligned with GPIO library usages.

> +	char *con_id = NULL;
> +	size_t new_size;
> +	int len;

...

> +	if (len >= sizeof(con) - 1) {

This can be transformed to check the returned value from strscpy().

> +		pr_err("%pOF: length of GPIO name \"%s\" exceeds current limit\n",
> +		       node, prop->name);
> +		return -EINVAL;
> +	}
> +
> +	if (len > 0) {
> +		strscpy(con, prop->name, len + 1);

The correct (robust) call is with destination size. Which means here that you
may use 2-argument strscpy().

> +		con_id = con;
> +	}

...

> +	if (!data->gpiods)
> +		return 0;

If it comes a new code (something else besides GPIOs and regulators) this will be a (small) impediment. Better to have a helper for each case and do

	ret = ..._gpiods();
	if (ret)
		...

Same for regulators and anything else in the future, if any.

> +		/*
> +		 * reset GPIOs normally have opposite polarity compared to

"reset"

> +		 * enable GPIOs. Instead of parsing the flags again, simply

"enable"

> +		 * set the raw value to high.

This is quite a fragile assumption. Yes, it would work in 98% cases, but will
break if it's not true somewhere else.

> +		 */

...

> +	/* largest post-reset-deassert delay seen in tree for Elan I2C HID */
> +	msleep(300);

Same Q, how do you monitor _all_ the drivers?

...

> +disable_gpios:
> +	for (gpio_i--; gpio_i >= 0; gpio_i--)
> +		gpiod_set_raw_value_cansleep(data->gpiods->desc[gpio_i], 0);

Can't you call the _array() variant here?

...

> -	dev_dbg(dev, "Resources: # of regulator supplies = %d\n", probe_data.regulators_num);
> +	dev_dbg(dev, "Resources: # of GPIOs = %d, # of regulator supplies = %d\n",
> +		probe_data.gpiods ? probe_data.gpiods->ndescs : 0,
> +		probe_data.regulators_num);

I would issue one message per class of the devices (GPIOs, regulators, ...)

-- 
With Best Regards,
Andy Shevchenko