From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH 02/12] drivers/gpio: provide optional timestamped readouts References: <20190124153428.21006-1-rpm@xenomai.org> <20190124153428.21006-3-rpm@xenomai.org> <4d1c39af-7a6f-1637-7727-ab6ad6d533c1@siemens.com> <40b168af-98d1-955d-ff01-ae5e70113744@xenomai.org> <197faf1a-c056-36fd-28ce-d8eee333b9cd@xenomai.org> <214e962e-f725-f056-7153-7225b21a4112@siemens.com> <1215ea5d-5ba7-348e-20b9-7d46cc77c183@xenomai.org> <76d6c198-2c6a-fa2c-8e0e-3ae92f7c2210@siemens.com> From: Philippe Gerum Message-ID: Date: Fri, 25 Jan 2019 11:11:23 +0100 MIME-Version: 1.0 In-Reply-To: <76d6c198-2c6a-fa2c-8e0e-3ae92f7c2210@siemens.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka , xenomai@xenomai.org On 1/25/19 10:48 AM, Jan Kiszka wrote: > On 25.01.19 10:38, Philippe Gerum wrote: >> On 1/25/19 10:33 AM, Jan Kiszka wrote: >>> On 25.01.19 10:31, Philippe Gerum wrote: >>>> On 1/25/19 10:23 AM, Jan Kiszka wrote: >>>>> On 25.01.19 10:15, Philippe Gerum wrote: >>>>>> On 1/24/19 7:17 PM, Jan Kiszka wrote: >>>>>>> On 24.01.19 16:34, Philippe Gerum wrote: >>>>>>>> In timestamping mode, read() returns the timestamp of the latest >>>>>>>> event >>>>>>>> receipt on the pin based on CLOCK_MONOTONIC, along with the pin >>>>>>>> state. This is an optional pin readout mode controlled by the >>>>>>>> GPIO_RTIOC_TS request, e.g.: >>>>>>>> >>>>>>>> struct rtdm_gpio_readout rdo; >>>>>>>> int ret, on, val; >>>>>>>> >>>>>>>> on = 1; >>>>>>>> ret = ioctl(pinfd, GPIO_RTIOC_TS, &on); >>>>>>>> ret = read(pinfd, &rdo, sizeof(rdo)); >>>>>>>> /* pin state changed to rdo.value at time rdo.timestamp */ >>>>>>>> >>>>>>>> on = 0; >>>>>>>> ret = ioctl(pinfd, GPIO_RTIOC_TS, &on); >>>>>>>> ret = read(pinfd, &val, sizeof(val)); >>>>>>>> /* pin state changed to value (time of change unspecified) */ >>>>>>>> >>>>>>>> By default, timestamping mode is disabled, which corresponds to the >>>>>>>> original behavior. >>>>>>>> >>>>>>>> Signed-off-by: Philippe Gerum >>>>>>>> --- >>>>>>>>      include/cobalt/kernel/rtdm/gpio.h |  1 + >>>>>>>>      include/rtdm/uapi/gpio.h          | 18 +++++++---- >>>>>>>>      kernel/drivers/gpio/gpio-core.c   | 54 >>>>>>>> +++++++++++++++++++++++-------- >>>>>>>>      3 files changed, 54 insertions(+), 19 deletions(-) >>>>>>>> >>>>>>>> diff --git a/include/cobalt/kernel/rtdm/gpio.h >>>>>>>> b/include/cobalt/kernel/rtdm/gpio.h >>>>>>>> index cdb472f8a..00055ec0a 100644 >>>>>>>> --- a/include/cobalt/kernel/rtdm/gpio.h >>>>>>>> +++ b/include/cobalt/kernel/rtdm/gpio.h >>>>>>>> @@ -33,6 +33,7 @@ struct rtdm_gpio_pin { >>>>>>>>          rtdm_event_t event; >>>>>>>>          char *name; >>>>>>>>          struct gpio_desc *desc; >>>>>>>> +    nanosecs_abs_t timestamp; >>>>>>>>      }; >>>>>>>>        struct rtdm_gpio_chip { >>>>>>>> diff --git a/include/rtdm/uapi/gpio.h b/include/rtdm/uapi/gpio.h >>>>>>>> index b745f156c..ac14be66c 100644 >>>>>>>> --- a/include/rtdm/uapi/gpio.h >>>>>>>> +++ b/include/rtdm/uapi/gpio.h >>>>>>>> @@ -18,12 +18,18 @@ >>>>>>>>      #ifndef _RTDM_UAPI_GPIO_H >>>>>>>>      #define _RTDM_UAPI_GPIO_H >>>>>>>>      -#define GPIO_RTIOC_DIR_OUT        _IOW(RTDM_CLASS_GPIO, 0, >>>>>>>> int) >>>>>>>> -#define GPIO_RTIOC_DIR_IN        _IO(RTDM_CLASS_GPIO, 1) >>>>>>>> -#define GPIO_RTIOC_IRQEN        _IOW(RTDM_CLASS_GPIO, 2, int) /* >>>>>>>> GPIO >>>>>>>> trigger */ >>>>>>>> -#define GPIO_RTIOC_IRQDIS        _IO(RTDM_CLASS_GPIO, 3) >>>>>>>> -#define GPIO_RTIOC_REQS                _IO(RTDM_CLASS_GPIO, 4) >>>>>>>> -#define GPIO_RTIOC_RELS                _IO(RTDM_CLASS_GPIO, 5) >>>>>>>> +struct rtdm_gpio_readout { >>>>>>>> +    __u64 timestamp; >>>>>>> >>>>>>> nanosecs_abs_t - we use this type also in to userspace interface. >>>>>>> >>>>>> >>>>>> Nope. This is ABI stuff, nanosecs_abs_t is not guaranteed to have the >>>>>> same size regardless of the ABI models, which is unsafe in mixed >>>>>> 32/64 >>>>>> model configurations. OTOH, __u64 is safe. >>>>> >>>>> If nanosecs_abs_t is alread an ABI, and it is used as such for a long >>>>> time (see include/rtdm/uapi/serial.h). If you see a bug in its >>>>> definition, that needs to be fixed. We should not resolve that by >>>>> choosing open-coded local workarounds. >>>>> >>>> >>>> nanosecs_t is not defined in the Xenomai ABI, never has been. Using >>>> nanosecs_t in structs actually abuses such ABI. So we may either keep >>>> adding even more nanosecs, or fix the spots where it should be replaced >>>> with __u64. >>> >>> Xenomai ABI includes the driver ABI - so your assumption might have been >>> it's not while it was de facto. >>> >>> Again, let's address the issue, not work around it. >>> >> >> __u64 is the fix, using nanosecs*_t in uapi/ is wrong. So please merge >> this fix, and we'll see how we can progress fixing other abuses. > > Nope: Adjust nanosecs_*_t if it has a problem ([u]int64_t vs. __u/s64 - > what's the problem exactly?), and use that. That will both address > existing users and future ones. No special solution for the GPIO driver > here. > I'm not pushing for a GPIO-specific solution, I'm pushing for using ABI-specific types which state their size explicitly in uapi/ data as much as possible, which is safer with mixed ABI models and would have spared me a lot of trouble back when I implemented the 32/64 ABI support for Xenomai. nanosecs_* is originally a kernel-side type which slipped in uapi/ structs, which does not state its size. The fact that nanosecs_* is defined as uint64_t but the kernel today does not address the issue at stake: there would be no obvious way to detect that a discrepancy might exist with what userland expects once such definition is modified for a different with if ever (which might be highly unlikely for nanosecs, but could happen for other types). -- Philippe.