Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751732AbdCQSzr (ORCPT ); Fri, 17 Mar 2017 14:55:47 -0400 Received: from lelnx194.ext.ti.com ([198.47.27.80]:51208 "EHLO lelnx194.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751166AbdCQSzH (ORCPT ); Fri, 17 Mar 2017 14:55:07 -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> CC: , , Santosh Shilimkar , Kevin Hilman , Linus Walleij , Alexandre Courbot , , , From: Grygorii Strashko Message-ID: Date: Fri, 17 Mar 2017 13:54:28 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170317135413.78118dc2.drivshin@awxrd.com> Content-Type: text/plain; charset="windows-1252" 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: 5397 Lines: 144 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. But agree - max might not be a good choose, so can you add dev_err() below, pls. > >> >>> } >>> >>> l = BIT(offset); >>> @@ -255,6 +258,8 @@ static void omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, >>> bank->context.debounce = debounce; >>> bank->context.debounce_en = val; >>> } >>> + >>> + return 0; >>> } >>> >>> /** >>> @@ -964,14 +969,15 @@ static int omap_gpio_debounce(struct gpio_chip *chip, unsigned offset, >>> { >>> struct gpio_bank *bank; >>> unsigned long flags; >>> + int ret; >>> >>> bank = gpiochip_get_data(chip); >>> >>> raw_spin_lock_irqsave(&bank->lock, flags); >>> - omap2_set_gpio_debounce(bank, offset, debounce); >>> + ret = omap2_set_gpio_debounce(bank, offset, debounce); >>> raw_spin_unlock_irqrestore(&bank->lock, flags); if (ret) dev_err(); >>> >>> - return 0; >>> + return ret; >>> } >>> >>> static int omap_gpio_set_config(struct gpio_chip *chip, unsigned offset, >>> >> > > -- regards, -grygorii