Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1032942AbdDTOop (ORCPT ); Thu, 20 Apr 2017 10:44:45 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:43007 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032121AbdDTOoj (ORCPT ); Thu, 20 Apr 2017 10:44:39 -0400 X-ME-Sender: X-Sasl-enc: kuevP7rEe5QARCiZB1gCQlT579bKWCYlXGDBtYVYTm9m 1492699478 Date: Thu, 20 Apr 2017 10:44:37 -0400 From: David Rivshin To: Grygorii Strashko Cc: , , Santosh Shilimkar , Kevin Hilman , Linus Walleij , Alexandre Courbot , , , Subject: Re: [PATCH 1/2] gpio: omap: return error if requested debounce time is not possible Message-ID: <20170420104437.7cd68de6.drivshin@awxrd.com> In-Reply-To: <20170317194235.5a883df8.drivshin@awxrd.com> 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> Organization: Allworx X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7655 Lines: 156 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). 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.