Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751235AbdCQXnj (ORCPT ); Fri, 17 Mar 2017 19:43:39 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:42990 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061AbdCQXnd (ORCPT ); Fri, 17 Mar 2017 19:43:33 -0400 X-ME-Sender: X-Sasl-enc: Tl6WgabxStRHvB7EiVujqJEpu/IYvREzYLjSjiAO5/tZ 1489794155 Date: Fri, 17 Mar 2017 19:42:35 -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: <20170317194235.5a883df8.drivshin@awxrd.com> In-Reply-To: <73fd00d4-6649-90d6-dcb1-0cd186055a69@ti.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> 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: 8743 Lines: 181 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. > > > > Of course that would be a change in behavior for any such existing DT, > > and it's conceivable that the DT for some HW is somehow relying on that > > previous incorrect behavior. I suspect it's more likely that they are > > silently broken, and no-one has noticed. A quick search of some in-tree > > DTs finds most debounce times are 5ms (which has no issue), and then > > these three examples (all happen to be gpio-keys): > > am335x-shc.dts: debounce-interval = <1000>; > > am335x-shc.dts: debounce-interval = <1000>; > > omap5-uevm.dts: debounce_interval = <50>; > > The first two currently result in a HW debounce of about 4ms. The > > third would be 2.5ms, except it's the wrong property name so it > > does nothing (it gets the default gpio-keys debounce of 5ms). > > Yep. looks like error in dt. There are mod such DTs actually > ./arch/arm/boot/dts/atlas7-evb.dts > ./arch/arm/boot/dts/emev2-kzm9d.dts > ./arch/arm/boot/dts/kirkwood-pogoplug-series-4.dts > ./arch/arm/boot/dts/omap5-uevm.dts > ./arch/arm/boot/dts/ste-snowball.dts Ah yes, I just grepped for 'debounce' in am* and omap*. I guess that typo has been copied over from DT to DT. I'm tempted to spin a patch correcting the typo, but I have no knowledge of those boards or HW to test with. Obviously no-one has complained about the 5ms vs 50ms debounce so far, so maybe 50ms isn't the correct number in the first place? > > > > Not having seen any of that hardware, I can't say for certain what the > > true HW requirements are. 1000ms does seem like a long debounce, perhaps > > the author meant 1ms (1000us) for those buttons? Or perhaps it really > > needs a 1000ms debounce, and is currently wrong? > > > >> > >> 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 ? I can spin a v2 as early as Monday, depending on the results of discussion on the second patch. > > > > > Tangent: > > This discussion makes me think that adding a gpiod_get_max_debounce() > > would allow even better behavior. Then asking for a too-high debounce > > could be a dev_err() in all gpio drivers, with the expectation that no > > driver should ask for such. Also, drivers could do something like use > > max hardware debounce plus a software debounce for the remaining time, > > in order to avoid CPU overhead on short glitches. > >