Messages in this thread | | | Date | Tue, 22 Nov 2011 00:52:03 +0200 | From | Denis Kuzmenko <> | Subject | Re: [PATCH] s3c/s3c24xx: arm: leds: Make s3c24xx LEDS driver use gpiolib |
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On 11/22/2011 12:03 AM, Stephen Warren wrote: > Denis Kuzmenko wrote at Monday, November 21, 2011 12:38 PM: >> On 11/21/2011 08:07 PM, Stephen Warren wrote: >>> Denis Kuzmenko wrote at Friday, November 18, 2011 4:17 PM: >>>> On 11/19/2011 12:44 AM, Stephen Warren wrote: > ... >>>>> OK, I see the need for a pull of some kind (although aren't there meant >>>>> to be ESD protection diodes for this purpose; relying on what are probably >>>>> pretty weak pullup/down resistors doesn't seem like it will provide much >>>>> protection at all). >>>> >>>> I don't mean pull as any kind of good protection. But it's much better >>>> to have it than not. >>> >>> Hmm. I'm not entirely convinced. If the board already has a pull-up/down, >>> it seems like it won't really make much difference to ESD, and you can't >>> make any assumptions in the core driver about whether such an external >>> resistor is already present. In fact, adding another pull resistor inside >>> the SoC in parallel will reduce the overall resistance, and increase wasted >>> power. >>> >> >> I don't think it's a real protection. It's rather "mistake-proofing" >> (Poka-Yoke). >> You are right, I didn't considered additional pulls (however I can't >> imagine tristate LED usage with additional external pull) and power >> consumptions. >> I was just wondering, why was pull needed in previous implementation. >> Additional ESD protection was the only thing I could imagine. I don't >> think it's needed there and I'm OK to remove pull-related code. >> So I'll remove it, test and send patch V3? > > I don't see any pulls being configured in the original code at all, > unless some of the s3c2410_* function have unexpected side-effect. The > only related thing is in probe: > > /* no point in having a pull-up if we are always driving */ > > if (pdata->flags & S3C24XX_LEDF_TRISTATE) { > .. > } else { > s3c2410_gpio_pullup(pdata->gpio, 0); > > which I assume disables an pull in the case where the pin is always driven. > > So, yes, I'd say submit v3 without any pull manipulation at all. >
Actually, "s3c2410_gpio_pullup(pdata->gpio, 0);" enables pull in the same way I've done that. Here is it's code:
/* gpiolib wrappers until these are totally eliminated */
void s3c2410_gpio_pullup(unsigned int pin, unsigned int to) { int ret;
WARN_ON(to); /* should be none of these left */
if (!to) { /* if pull is enabled, try first with up, and if that * fails, try using down */
ret = s3c_gpio_setpull(pin, S3C_GPIO_PULL_UP); if (ret) s3c_gpio_setpull(pin, S3C_GPIO_PULL_DOWN); } else { s3c_gpio_setpull(pin, S3C_GPIO_PULL_NONE); } }
So pull is enabled in same "random" way as I did but for *opposite* state of S3C24XX_LEDF_TRISTATE flag. And again:
>> I was just wondering, why was pull needed in previous implementation. >> Additional ESD protection was the only thing I could imagine. I don't >> think it's needed there and I'm OK to remove pull-related code. >> So I'll remove it, test and send patch V3?
-- Best regards, Denis Kuzmenko.
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