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Date: Fri, 18 Nov 2011 23:00:53 +0200
From: Denis Kuzmenko <linux@...onet.org.ua>
To: Stephen Warren <swarren@...dia.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Grant Likely <grant.likely@...retlab.ca>,
Linus Walleij <linus.walleij@...aro.org>,
Richard Purdie <rpurdie@...ys.net>,
Wolfram Sang <w.sang@...gutronix.de>
Subject: Re: [PATCH] s3c/s3c24xx: arm: leds: Make s3c24xx LEDS driver use
gpiolib
On 11/18/2011 07:08 PM, Stephen Warren wrote:
> Denis Kuzmenko wrote at Thursday, November 17, 2011 1:47 PM:
>> Make s3c24xx LEDS driver use gpiolib.
>
> I made some slightly nit-picky
> comments below.
Thanks for looking my patch.
>> diff --git a/drivers/leds/leds-s3c24xx.c b/drivers/leds/leds-s3c24xx.c
>
>> static void s3c24xx_led_set(struct led_classdev *led_cdev,
>> - enum led_brightness value)
>> + enum led_brightness value)
>
> Seems unnecessary, but is probably fine.
That was made unintentionally - will fix in next version.
>> {
>> struct s3c24xx_gpio_led *led = to_gpio(led_cdev);
>> struct s3c24xx_led_platdata *pd = led->pdata;
>>
>> - /* there will be a short delay between setting the output and
>> - * going from output to input when using tristate. */
>> -
>> - s3c2410_gpio_setpin(pd->gpio, (value ? 1 : 0) ^
>> - (pd->flags & S3C24XX_LEDF_ACTLOW));
>> -
>> - if (pd->flags & S3C24XX_LEDF_TRISTATE)
>> - s3c2410_gpio_cfgpin(pd->gpio,
>> - value ? S3C2410_GPIO_OUTPUT : S3C2410_GPIO_INPUT);
>> + /*
>> + * ensure value is 0 or 1 to use it with bitwise XOR (^)
>> + * (only 100% brightness is supported)
>> + */
>> + value = value ? 1 : 0;
>> +
>> + if (pd->flags & S3C24XX_LEDF_TRISTATE) {
>> + if (value) {
>> + /* invert value if S3C24XX_LEDF_ACTLOW is set */
>> + value = (pd->flags & S3C24XX_LEDF_ACTLOW) ^ value;
>> + gpio_direction_output(pd->gpio, value);
>> + } else {
>> + gpio_direction_input(pd->gpio);
>> + }
>> + } else {
>> + /* invert value if S3C24XX_LEDF_ACTLOW is set */
>> + value = (pd->flags & S3C24XX_LEDF_ACTLOW) ^ value;
>> + gpio_set_value(pd->gpio, value);
>> + }
>
> I'd be tempted to simplify the new code a little:
>
> /* invert value if S3C24XX_LEDF_ACTLOW is set */
> value = !!(pd->flags & S3C24XX_LEDF_ACTLOW) ^ !!value;
>
> if (pd->flags & S3C24XX_LEDF_TRISTATE) {
> if (value)
> gpio_direction_output(pd->gpio, value);
> else
> gpio_direction_input(pd->gpio);
> } else {
> gpio_set_value(pd->gpio, value);
> }
I've almost broke my mind writing this part and you've repeated my
mistake: in line where 'value' is checked ( if(value) ) the 'value'
shouldn't be inverted independently of S3C24XX_LEDF_ACTLOW flag.
This because S3C24XX_LEDF_TRISTATE means "tristate to turn off"
(arch/arm/mach-s3c2410/include/mach/leds-gpio.h:18) - that produces all
of complexity. Hope my description is understandable (if not, I'm sorry
- my English is too bad for this).
>> @@ -76,7 +88,8 @@ static int s3c24xx_led_probe(struct platform_device *dev)
>> led = kzalloc(sizeof(struct s3c24xx_gpio_led), GFP_KERNEL);
>> if (led == NULL) {
>> dev_err(&dev->dev, "No memory for device\n");
>> - return -ENOMEM;
>> + ret = -ENOMEM;
>> + goto err_kzalloc;
>> }
>
> That works fine, but isn't strictly necessary; no previous allocations
> have been made here that need to be undone.
>
I tried to use same error handling approach in all code, but you are
right - I've missed that in this place we can return safely and not
loosing much of code readability. _But_ this violates approach of not
having multiple returns unless you *really* need this. Still in doubt...
>> @@ -91,12 +104,15 @@ static int s3c24xx_led_probe(struct platform_device
>> *dev)
>> /* no point in having a pull-up if we are always driving */
>>
>> if (pdata->flags & S3C24XX_LEDF_TRISTATE) {
>> - s3c2410_gpio_setpin(pdata->gpio, 0);
>> - s3c2410_gpio_cfgpin(pdata->gpio, S3C2410_GPIO_INPUT);
>> + ret = gpio_request_one(pdata->gpio, GPIOF_IN, pdata->name);
>> } else {
>> - s3c2410_gpio_pullup(pdata->gpio, 0);
>> - s3c2410_gpio_setpin(pdata->gpio, 0);
>> - s3c2410_gpio_cfgpin(pdata->gpio, S3C2410_GPIO_OUTPUT);
>> + ret = gpio_request_one(pdata->gpio, GPIOF_OUT_INIT_LOW,
>> + pdata->name);
>> + s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_NONE);
>> + }
>
> I always prefer not to duplicate function calls, but rather to calculate
> the differing data (either directly in the call, or into a temporary
> variable first), so:
>
> ret = gpio_request_one(pdata->gpio,
> (pdata->flags & S3C24XX_LEDF_TRISTATE) ?
> GPIOF_IN : GPIOF_OUT_INIT_LOW,
> pdata->name);
>
> if (!(pdata->flags & S3C24XX_LEDF_TRISTATE))
> s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_NONE);
>
>
>> + if (ret < 0) {
>> + dev_err(&dev->dev, "gpio_request failed\n");
>> + goto err_gpio_request;
>> }
>
> You should probably move that error check right after calling
> gpio_request_one()
>
I see no big difference between those two variants, but:
1. my code looks for more readable
2. your code allows not to call 's3c_gpio_setpull' in case of
gpio_request fail which looks like the _only_ usable variant.
Besides that, I've made a mistake changing
s3c2410_gpio_pullup(pdata->gpio, 0)
to
s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_NONE)
because first variant actually means *enable* pull, trying first UP and,
if fail, DOWN direction. So pull-resistor is enabled in this case but in
some *random* direction.
The only use case for pull-resistor I see here is not to left pin
floating if someone configured _tristate_off_ LED on pin which actually
don't have it (LED or anything other connected). Considering this and a
fact that pullup is default enabled I think that it's safe to remove
it's configuration at all and left code in my variant. Or to add
pull-resistor enabling code for *opposite* case (S3C24XX_LEDF_TRISTATE).
--
Best regards, Denis Kuzmenko.
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