Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751303AbdCQSbb (ORCPT ); Fri, 17 Mar 2017 14:31:31 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:51115 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750999AbdCQSb2 (ORCPT ); Fri, 17 Mar 2017 14:31:28 -0400 X-ME-Sender: X-Sasl-enc: mMAP9E7qEZ/BCc8n2VkTOZo+DQNPA7EP5zocFzpsPcuL 1489773254 Date: Fri, 17 Mar 2017 13:54:13 -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: <20170317135413.78118dc2.drivshin@awxrd.com> In-Reply-To: References: <20170317005704.11971-1-drivshin@awxrd.com> <20170317005704.11971-2-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: 4936 Lines: 126 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? > > > } > > > > 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); > > > > - return 0; > > + return ret; > > } > > > > static int omap_gpio_set_config(struct gpio_chip *chip, unsigned offset, > > >