Date: Fri, 27 Nov 2020 21:30:24 -0300 From: "Dr. Rolf Jansen" <freebsd-rj@obsigna.com> To: Ian Lepore <ian@freebsd.org> Cc: freebsd-arm@freebsd.org Subject: Re: User Space GPIO Interrupt programming - GSoC-2018 Message-ID: <3F7009F8-549C-4580-B4D2-9C8471890CE6@obsigna.com> In-Reply-To: <ed2079c342f64b611e014fb5331e2be8beeed547.camel@freebsd.org> References: <2B01780F-D367-48A3-A827-B479030A496D@obsigna.com> <c55d7f332631b69c3241a60538a6a7b5475d93b9.camel@freebsd.org> <FBEF19B1-0504-4CDF-976C-C50707E06584@obsigna.com> <ed2079c342f64b611e014fb5331e2be8beeed547.camel@freebsd.org>
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Am 27.11.2020 um 14:32 schrieb Ian Lepore <ian@freebsd.org>: > On Thu, 2020-11-26 at 22:18 -0300, Dr. Rolf Jansen wrote: >>> Am 26.11.2020 um 16:56 schrieb Ian Lepore <ian@freebsd.org>: >>>=20 >>> On Tue, 2020-11-24 at 17:14 -0300, Dr. Rolf Jansen wrote: >>>> Hello >>>>=20 >>>> Has anything of the GSoC-2018 efforts made it into the current >>>> code >>>> base? >>>>=20 >>>>=20 >>>=20 >>>=20 > = https://wiki.freebsd.org/SummerOfCode2018Projects/UserSpaceGPIOinterrupts >>>>=20 >>>> I installed the recent 13.0-CURRENT snapshot (2020-11-19) on a >>>> BeagleBone Black which was one of the implementation targets of >>>> said >>>> project, but when running the test tools, I either see cannot >>>> read/kevent/poll/aio_read - Operation not supported by device or >>>> Inappropriate ioctl for device. >>>>=20 >>>> Perhaps I need to pull the project=1B$B!-=1B(Bs changes into the = kernel by >>>> myself. However, before this I would like to ask whether it is >>>> worth >>>> the effort. >>>>=20 >>>> Please, can anyone shed some light on this. >>>>=20 >>>> Best regards >>>>=20 >>>> Rolf >>>>=20 >>>=20 >>> I made some time this morning to review the gsoc2018 code. It >>> turns >>> out this code is very high quality, nearly ready to commit as- >>> is. The >>> main thing it needs is some style cleanup in its comment blocks, >>> and >>> documentation. I'd be inclined to commit the code first and write >>> the >>> documentation over the next little while and commit it separately. >>>=20 >>> If you'd like to give it a try, here's a diff that should apply and >>> build cleanly on freebsd 12 or 13: >>>=20 >>> https://people.freebsd.org/~ian/gpio_gsoc2018.diff >>>=20 >>> While there isn't any documentation yet, there is a test program (I >>> haven't run it yet) that demonstrates all the features: >>>=20 >>>=20 > = https://github.com/ckraemer/gsoc2018-utils/blob/master/src/gpioc_intr_test= .c >>>=20 >>> Right now the code will let you block waiting for a pin-change >>> event >>> using select(), poll() or kevents, or to be notified via SIGIO, but >>> after being notified that something happened, you still have to >>> call >>> read() to see which pin changed. I think if the pin changes state >>> multiple times between calls to read(), you'll lose track of some >>> changes (I'm not positive of that, I don't understand the kevent >>> stuff >>> well). >>>=20 >>> I'd like to add some features so that you can configure it to track >>> pin >>> changes in counting-mode and timestamping-mode. In counting mode, >>> when >>> you do a read() you would get back a pair of values, the pin number >>> and >>> how many times its interrupt fired since the last read. In >>> timestamping mode, every read would return a pin number and an >>> associated timespec giving the exact time the interrupt happened >>> (there >>> would need to be a way to configure how many events it could >>> buffer, >>> but I think even allowing a thousand buffered events would only use >>> a >>> few kbytes of memory). >>=20 >> I got it working as well, please see my other post from yesterday. I >> used gpioc_intr_test.c. >>=20 >> I see hundreds of warning messages when I press the test button a few >> times. May these warnings be safely ignored. The kernel module of >> Oskar Holmund works quite nice as well (for what I need), and with >> that one, I don=1B$B!G=1B(Bt see warnings. >>=20 >> The counting- and timestamping-mode for sure would be very useful. >> Perhaps by implementing this, there won=1B$B!G=1B(Bt be no unhandled = interrupts >> anymore, and hence there won=1B$B!G=1B(Bt be any warnings either. >>=20 >> Best regards >>=20 >> Rolf >=20 > I'm sorry, I somehow overlooked your previous message about using > gpioc_intr_test.c. >=20 > Those warning messages are definitely not a good thing, in some = changes > I've made to the original patches they are changed to debugging-only > output that won't normally show up. Printing messages from within an > interrupt handler is pretty much always a bad idea. :) >=20 > I was thinking about the various interrupt options and realized we > cannot support level-triggered interrupts in this code without a ton = of > work. It's just a recipe for an interrupt storm (which will happen at > the rate of tens of thousands of interrupts per second once the = printfs > aren't there to slow things down to console IO speed). To use level- > triggered interrupts from userland, the gpioc would have to mask the > interrupt from within the interrupt handler (we don't have an internal > API for doing that with gpio interrupts right now), and provide some > sort of EOI (end-of-interrupt) acknowledgement interface to userland = to > unmask them once it had done something to make the interrupt stop > asserting. Basically this would extend the way device drivers handle > level-triggered interrupts into userland, and I just don't see much > value in all the work that would be involved to make that happen. >=20 > I think instead we should just run in counting-mode by default, and = add > new code similar to what Vladimir Goncharov has proposed to handle > detailed reporting of each event if the app requests it. >=20 > I can't make up my mind on the issue of debouncing. My gut tells me > that building in some kind of debounce logic as a per-pin configurable > option would be nice, but it might also get really complicated. An = app > could handle debouncing for itself if it requested detailed event > reporting, because the timestamps on the events could help it decide > what to do. After working a bit with the various "User Space GPIO Interrupt" = incarnations in the last few days, I found that I don't need level = interrupts. The hardware colleague of our present project told me that I = do not need to bother with button debouncing in software either. There = are IC's which manage this, for example: MAX6818 - = https://datasheets.maximintegrated.com/en/ds/1896.pdf. So, the GPIO = would see only perfect square wave signals when a button has been = pressed. I still think that counting-mode and timestamp-mode could be very = useful. Regarding the memory allocation, I am with you that it should be done = once and not for any interrupt trail. As a matter of fact I did kind of = this already for a kernel module for FreeBSD-x86-64 targets which I = wrote for National Instruments M- and X-Series PCI and PCIe DAQ boards. = Here I allocate huge blocks of DMA memory (256 MB for the AI channels = and 48 MB for the AO channels) in the course of xxx_attach() and this = can be mapped into user space by mmap(). I added sysctls which allow to = resize said memory blocks, and ioctls for clearing and synching the = buffers. I do all the math on the measurement data in user space by = directly accessing the DMA blocks in the course of the measurements. Thinking about it, wouldn't it be nice to mmap() the = interrupt/counter/timestamp table into user space? Programs could read = the data in the table directly. It could be a round robin table, perhaps = of 100 kB to 1 MB. Perhaps my code in my kernel module for DMA buffer = management, which could be easily switched to any-kind-of-memory = management, does not exactly meet the high quality and style of FreeBSD = code, and I am even hesitant to offer it. However, if you are curious, = please send me a note. Best regards Rolf=
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