[PATCH 02/12] drivers/gpio: provide optional timestamped readouts

Philippe Gerum rpm at xenomai.org
Fri Jan 25 11:11:23 CET 2019


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 <rpm at xenomai.org>
>>>>>>>> ---
>>>>>>>>      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.



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