Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S970484AbdDTPVO (ORCPT ); Thu, 20 Apr 2017 11:21:14 -0400 Received: from fllnx209.ext.ti.com ([198.47.19.16]:50919 "EHLO fllnx209.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S970407AbdDTPVL (ORCPT ); Thu, 20 Apr 2017 11:21:11 -0400 Subject: Re: [PATCH 1/2] gpio: omap: return error if requested debounce time is not possible To: David Rivshin References: <20170317005704.11971-1-drivshin@awxrd.com> <20170317005704.11971-2-drivshin@awxrd.com> <20170317135413.78118dc2.drivshin@awxrd.com> <20170317165032.5b891bc1.drivshin@awxrd.com> <73fd00d4-6649-90d6-dcb1-0cd186055a69@ti.com> <20170317194235.5a883df8.drivshin@awxrd.com> <20170420104437.7cd68de6.drivshin@awxrd.com> CC: , , Santosh Shilimkar , Kevin Hilman , Linus Walleij , Alexandre Courbot , , , From: Grygorii Strashko Message-ID: Date: Thu, 20 Apr 2017 10:19:35 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170420104437.7cd68de6.drivshin@awxrd.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [128.247.83.96] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7644 Lines: 168 On 04/20/2017 09:44 AM, David Rivshin wrote: > Hi Grygorii, > > Not sure if you saw the question at the bottom asking for clarification > on what you'd prefer as far as any dev_xxx() message for this case. If > there is still concern on the other patch, I could just resubmit this > standalone (perhaps aiming for 4.12 at this point). Could you add dev info and resubmit this alone, pls > > On Fri, 17 Mar 2017 19:42:35 -0400 > David Rivshin wrote: > >> On Fri, 17 Mar 2017 16:43:56 -0500 >> Grygorii Strashko wrote: >> >>> On 03/17/2017 03:50 PM, David Rivshin wrote: >>>> On Fri, 17 Mar 2017 13:54:28 -0500 >>>> Grygorii Strashko wrote: >>>> >>>>> On 03/17/2017 12:54 PM, David Rivshin wrote: >>>>>> Hi Grygorii, >>>>>> >>>>>> On Fri, 17 Mar 2017 11:45:56 -0500 >>>>>> Grygorii Strashko wrote: >>>>>> >>>>>>> On 03/16/2017 07:57 PM, David Rivshin wrote: >>>>>>>> From: David Rivshin >>>>>>>> >>>>>>>> omap_gpio_debounce() does not validate that the requested debounce >>>>>>>> is within a range it can handle. Instead it lets the register value >>>>>>>> wrap silently, and always returns success. >>>>>>>> >>>>>>>> This can lead to all sorts of unexpected behavior, such as gpio_keys >>>>>>>> asking for a too-long debounce, but getting a very short debounce in >>>>>>>> practice. >>>>>>>> >>>>>>>> Fix this by returning -EINVAL if the requested value does not fit into >>>>>>>> the register field. If there is no debounce clock available at all, >>>>>>>> return -ENOTSUPP. >>>>>>> >>>>>>> In general this patch looks good, but there is one thing I'm worry about.. >>>>>>> >>>>>>>> >>>>>>>> Fixes: e85ec6c3047b ("gpio: omap: fix omap2_set_gpio_debounce") >>>>>>>> Cc: # 4.3+ >>>>>>>> Signed-off-by: David Rivshin >>>>>>>> --- >>>>>>>> drivers/gpio/gpio-omap.c | 16 +++++++++++----- >>>>>>>> 1 file changed, 11 insertions(+), 5 deletions(-) >>>>>>>> >>>>>>>> diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c >>>>>>>> index efc85a2..33ec02d 100644 >>>>>>>> --- a/drivers/gpio/gpio-omap.c >>>>>>>> +++ b/drivers/gpio/gpio-omap.c >>>>>>>> @@ -208,8 +208,10 @@ static inline void omap_gpio_dbck_disable(struct gpio_bank *bank) >>>>>>>> * OMAP's debounce time is in 31us steps >>>>>>>> * = (GPIO_DEBOUNCINGTIME[7:0].DEBOUNCETIME + 1) x 31 >>>>>>>> * so we need to convert and round up to the closest unit. >>>>>>>> + * >>>>>>>> + * Return: 0 on success, negative error otherwise. >>>>>>>> */ >>>>>>>> -static void omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, >>>>>>>> +static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, >>>>>>>> unsigned debounce) >>>>>>>> { >>>>>>>> void __iomem *reg; >>>>>>>> @@ -218,11 +220,12 @@ static void omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, >>>>>>>> bool enable = !!debounce; >>>>>>>> >>>>>>>> if (!bank->dbck_flag) >>>>>>>> - return; >>>>>>>> + return -ENOTSUPP; >>>>>>>> >>>>>>>> if (enable) { >>>>>>>> debounce = DIV_ROUND_UP(debounce, 31) - 1; >>>>>>>> - debounce &= OMAP4_GPIO_DEBOUNCINGTIME_MASK; >>>>>>>> + if ((debounce & OMAP4_GPIO_DEBOUNCINGTIME_MASK) != debounce) >>>>>>>> + return -EINVAL; >>>>>>> >>>>>>> This might cause boot issues as current drivers may expect this op to succeed even if >>>>>>> configured value is wrong - just think, may be we can do warn here and use max value as >>>>>>> fallback? >>>>>> >>>>>> I have not looked through all drivers to be sure, but at least the gpio-keys >>>>>> driver requires set_debounce to return an error if it can't satisfy the request. >>>>>> In that case gpio-keys will use a software timer instead. >>>>>> >>>>>> if (button->debounce_interval) { >>>>>> error = gpiod_set_debounce(bdata->gpiod, >>>>>> button->debounce_interval * 1000); >>>>>> /* use timer if gpiolib doesn't provide debounce */ >>>>>> if (error < 0) >>>>>> bdata->software_debounce = >>>>>> button->debounce_interval; >>>>>> } >>>>>> >>>>>> Also, at least some other GPIO drivers (e.g. gpio-max7760) return -EINVAL in >>>>>> such a case. And gpiolib will return -ENOTSUPP if there is no debounce >>>>>> callback at all. So I expect all drivers which use gpiod_set_debounce() to >>>>>> handle error returns gracefully. >>>>>> >>>>>> So I certainly understand the concern about backwards compatibility, but I >>>>>> think clipping to max is the greater of the evils in this case. Even a >>>>>> warning may be too much, because it's not necessarily anything wrong. >>>>>> Perhaps an info or debug message would be helpful, though? >>>>>> >>>>>> If you prefer, I can try to go through all callers of gpiod_set_debounce() >>>>>> and see how they'd handle an error return. The handful I've looked through so >>>>>> far all behave like gpio-keys. The only ones I'd be particularly concerned >>>>>> about are platform-specific drivers which were perhaps never used with other >>>>>> gpio drivers. Do you know of that I should pay special attention to? >>>>> >>>>> Yeh agree. But the problem here will be not only with drivers itself - it can be wrong data in DT :( >>>>> As result, even gpio-keys driver will just silently switch to software_debounce >>>>> without any notification. >>>> >>>> I think that switching to software_debounce silently is exactly the >>>> intended/desired behavior of gpio-keys (and other drivers). For example, >>>> if the DT requests a 20ms debounce on a gpio-key, the existing math >>>> resulted in a hardware debounce of just 2ms. With the error return, >>>> gpio-keys would silently switch to software_debounce of the requested >>>> 20ms (potentially longer if the CPU is busy, but I don't think that's >>>> a problem for correctness), exactly what the DT asked for. >>>> > [...snip...] >>>>> >>>>> But agree - max might not be a good choose, so can you add dev_err() below, pls. >>>> >>>> Given the above, I personally feel that a dev_err() is undesirable in most >>>> cases. If I have a system and matching DT that just happens to need a longer >>>> debounce than the GPIO HW is capable of, gpio-keys (etc) does the best it can automatically. I don't consider that there is any error in that case, or >>>> anything to be fixed. >>>> I can understanding wanting to draw attention to a change in behavior (just >>>> in case the DT is incorrect), but I'd personally lean towards dev_info() if >>>> anything. >>>> >>>> That said: if you still prefer dev_err(), I will certainly do so. >>> >>> Fair enough :) thanks. >>> >>> Acked-by: Grygorii Strashko >> >> Just to make sure I don't misunderstand, would you like me to: >> A) put in a dev_err() >> B) put in a dev_info() >> C) leave it as-is without any message >> ? >> > [...snip...] > > FYI, I have searched for all uses of gpio{,d}_set_debounce (in v4.11-rc1), > and found nothing concerning. Most drivers fall back to software debounce. > > The only exception I found was mmc_spi (via mmc_gpio_request_cd), but the > only time that has a non-zero debounce requested is for vision_ep9307 which > is hardcoded to ask for a 1us debounce via platform data. I don't believe > ep93xx would use the gpio-omap driver anyways. The mmc-spi-slot devicetree > binding doesn't support setting a debounce on any of the GPIOs. > -- regards, -grygorii