linux-kernel - Re: [PATCH v5 4/4] gpio: add support for the Diolan DLN-2 USB GPIO driver

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Date:	Sat, 20 Sep 2014 04:48:47 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	gregkh@...uxfoundation.org, linus.walleij@...aro.org,
	gnurou@...il.com, wsa@...-dreams.de, sameo@...ux.intel.com,
	lee.jones@...aro.org, johan@...nel.org, daniel.baluta@...el.com,
	laurentiu.palcu@...el.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v5 4/4] gpio: add support for the Diolan DLN-2 USB GPIO driver

On Friday 19 September 2014, Octavian Purdila wrote:
> +struct dln2_gpio_pin {
> +	__le16 pin;
> +} __packed;

This does not need to be marked packed, since it is never embedded in another
structure.

> +struct dln2_gpio_pin_val {
> +	__le16 pin;
> +	u8 value;
> +} __packed;

It's enough here to mark just the 'pin' member as packed.

> +static int dln2_gpio_get_pin_count(struct platform_device *pdev)
> +{
> +	int ret;
> +	__le16 count;
> +	int len = sizeof(count);
> +
> +	ret = dln2_transfer(pdev, DLN2_GPIO_GET_PIN_COUNT, NULL, 0, &count,
> +			    &len);

You must not do a USB transaction on stack memory.

> +static int dln2_gpio_pin_cmd(struct dln2_gpio *dln2, int cmd, unsigned pin)
> +{
> +	struct dln2_gpio_pin req = {
> +		.pin = cpu_to_le16(pin),
> +	};
> +
> +	return dln2_transfer(dln2->pdev, cmd, &req, sizeof(req), NULL, NULL);
> +}

Same here

> +static int dln2_gpio_pin_val(struct dln2_gpio *dln2, int cmd, unsigned int pin)
> +{
> +	int ret;
> +	struct dln2_gpio_pin req = {
> +		.pin = cpu_to_le16(pin),
> +	};
> +	struct dln2_gpio_pin_val rsp;

And here.

> +static int dln2_gpio_set_debounce(struct gpio_chip *chip, unsigned offset,
> +				  unsigned debounce)
> +{
> +	struct dln2_gpio *dln2 = container_of(chip, struct dln2_gpio, gpio);
> +	struct {
> +		__le32 duration;
> +	} __packed req = {
> +		.duration = cpu_to_le32(debounce),
> +	};
> +
> +	return dln2_transfer(dln2->pdev, DLN2_GPIO_SET_DEBOUNCE,
> +			     &req, sizeof(req), NULL, NULL);
> +}

Here you also have a strange __packed attribute that makes no sense
for a local variable, in addition to the stack problem.

I think the only correct way to handle these is to add a dynamic
allocation of an entire page for the DMA, which can probably be
part of the dln2_transfer function so you don't have to do it
in each caller.

	Arnd
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