Message-ID: <d118e4ed-3faf-ebfc-1ad3-ba3d2c1178eb@maciej.szmigiero.name>
Date:   Thu, 4 Jan 2018 00:41:51 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Jonathan Cameron <jic23@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH v3] gpio: winbond: add driver

On 03.01.2018 20:05, Andy Shevchenko wrote:
> On Sat, 2017-12-30 at 22:02 +0100, Maciej S. Szmigiero wrote:
>> This commit adds GPIO driver for Winbond Super I/Os.
>>
>> Currently, only W83627UHG model (also known as Nuvoton NCT6627UD) is
>> supported but in the future a support for other Winbond models, too,
>> can
>> be added to the driver.
>>
>> A module parameter "gpios" sets a bitmask of GPIO ports to enable (bit
>> 0 is
>> GPIO1, bit 1 is GPIO2, etc.).
>> One should be careful which ports one tinkers with since some might be
>> managed by the firmware (for functions like powering on and off,
>> sleeping,
>> BIOS recovery, etc.) and some of GPIO port pins are physically shared
>> with
>> other devices included in the Super I/O chip.
>>
> 
> Thanks for an update.
> My comments below.
> 
> First of all, looking more at this driver, why don't we create a
> gpiochip per real "port" during actual configuration?

Hmm.. there is only a one 'chip' here, so why would the driver want to
register multiple ones?

That would also create at least one additional point of failure if
one or more such gpiochip(s) register but one fails to do so.

> And I still have filing that this one suitable for MFD.

As I wrote previously, that would necessitate rewriting also w83627ehf
hwmon and w83627hf_wdt drivers, and would make the driver stand out
against other, similar Super I/O drivers.

> Anyone, does it make sense?
> 
>> +#define WB_SIO_REG_G1MF_G2PP		7
>> +#define WB_SIO_REG_G1MF_G1PP		6
> 
> Forgot to swap.

Good catch, will swap.

> 
>> +#define wb_sio_notice(...) pr_notice(WB_GPIO_DRIVER_NAME ": "
>> __VA_ARGS__)
>> +#define wb_sio_warn(...) pr_warn(WB_GPIO_DRIVER_NAME ": "
>> __VA_ARGS__)
>> +#define wb_sio_err(...) pr_err(WB_GPIO_DRIVER_NAME ": " __VA_ARGS__)
> 
> What I meant is to
> 
> #define pr_fmt(x) ...
> 
> Look at the kernel sources, there are a lot of examples.

I see now what you meant, will do it then.

>> +/* returns whether changing a pin is allowed */
>> +static bool winbond_gpio_get_info(unsigned int *gpio_num,
>> +				  const struct winbond_gpio_info
>> **info)
>> +{
>> +	bool allow_changing = true;
>> +	unsigned long i;
>> +
>> +	for_each_set_bit(i, &gpios, sizeof(gpios)) {
>> +		if (*gpio_num < 8)
>> +			break;
>> +
>> +		*gpio_num -= 8;
>> +	}
> 
> Why not hweight() here?
> 
> unsigned int shift = hweight_long(gpios) * 8;
> unsigned int index = fls_long(gpios); // AFAIU
> 
> *offset -= *offset >= shift ? shift : shift - 8;
> *info = &winbond_gpio_infos[index];
> 
> ...

Unfortunately, this code doesn't produce the same results as the code
above.

First, in this code "index" does not depend on "gpio_num" (or "offset")
passed to winbond_gpio_get_info() function, so gpio 0 (on the first GPIO
device or port) will access the same winbond_gpio_infos entry as gpio 18
(which is located on the third GPIO port).
In fact, the calculated "index" would always point to the last enabled
GPIO port (since that is the meaning of "gpios" MSB, assuming this
user-provided parameter was properly verified or sanitized).

Second, the calculated "offset" would end negative for anything but the
very last GPIO port (ok, not really negative since it is an unsigned type,
but still not correct either).
And that even not taking into account the special case of GPIO6 port
that has only 5 gpios.

What we want in this code is for "i" (or "index") to contain the GPIO
port number for the passed "gpio_num" (or "offset") and that this
last variable ends reduced modulo 8 from its original value.

>> +
>> +	*info = &winbond_gpio_infos[i];
>> +
>> +	/*
>> +	 * GPIO2 (the second port) shares some pins with a basic PC
>> +	 * functionality, which is very likely controlled by the
>> firmware.
>> +	 * Don't allow changing these pins by default.
>> +	 */
>> +	if (i == 1) {
>> +		if (*gpio_num == 0 && !pledgpio)
>> +			allow_changing = false;
>> +		else if (*gpio_num == 1 && !beepgpio)
>> +			allow_changing = false;
>> +		else if ((*gpio_num == 5 || *gpio_num == 6) &&
>> !i2cgpio)
>> +			allow_changing = false;
>> +	}
>> +
>> +	return allow_changing;
>> +}
> 
>> +static int winbond_gpio_configure(unsigned long base)
>> +{
>> +	unsigned long i;
>> +
>> +	for_each_set_bit(i, &gpios, sizeof(gpios))
>> +		if (!winbond_gpio_configure_port(base, i))
>> +			gpios &= ~BIT(i);
> 
>> +
>> +	if (!gpios) {
>> +		wb_sio_err("please use 'gpios' module parameter to
>> select some active GPIO ports to enable\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	return 0;
>> +}
>>
> 
>> +static int winbond_gpio_imatch(struct device *dev, unsigned int id)
>> +{
>> +	int ret;
>> +
> 
>> +	if (gpios & ~GENMASK(ARRAY_SIZE(winbond_gpio_infos) - 1, 0))
>> {
>> +		wb_sio_err("unknown ports enabled in GPIO ports
>> bitmask\n");
>> +		return 0;
>> +	}
> 
> Do we care? Perhaps just enforce mask based on the size and leave
> garbage out.

Can be done either way, but I think notifying user that he or she has
provided an incorrect parameter value is a good thing - we can use a
accept-but-warn style.

> 
>> +	/*
>> +	 * if the 'base' module parameter is unset probe two chip
>> default
>> +	 * I/O port bases
>> +	 */
>> +	baseparam = WB_SIO_BASE;
>> +	ret = winbond_gpio_check_chip(baseparam);
>> +	if (ret == 0)
>> +		return 1;
> 
>> +	else if (ret != -ENODEV && ret != -EBUSY)
> 
> Redundant 'else'.

Will remove.

>> +		return 0;
>> +
>> +	baseparam = WB_SIO_BASE_HIGH;
>> +	return winbond_gpio_check_chip(baseparam) == 0;
>> +}
>> +
>> +static int winbond_gpio_iprobe(struct device *dev, unsigned int id)
>> +{
>> +	int ret;
>> +
>> +	if (baseparam == 0)
>> +		return -EINVAL;
>> +
>> +	ret = winbond_sio_enter(baseparam);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = winbond_gpio_configure(baseparam);
> 
> ...like registering MFD children in that call directly?
>
>> +
>> +	winbond_sio_leave(baseparam);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	/*
>> +	 * Add 8 gpios for every GPIO port that was enabled in gpios
>> +	 * module parameter (that wasn't disabled earlier in
>> +	 * winbond_gpio_configure() & co. due to, for example, a pin
>> conflict).
>> +	 */
> 
>> +	winbond_gpio_chip.ngpio = hweight_long(gpios) * 8;
>> +
>> +	/*
>> +	 * GPIO6 port has only 5 pins, so if it is enabled we have to
>> adjust
>> +	 * the total count appropriately
>> +	 */
>> +	if (gpios & BIT(5))
>> +		winbond_gpio_chip.ngpio -= (8 - 5);
> 
> So, if we still are going use this, taking into consideration above
> proposal, it would make sense just to cache values in some internal
> struct and use above, right?

If it turns out we would need this value somewhere we can simply read
it from struct gpio_chip that gpiolib passes to callback functions.

Maciej

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