----- Den 16 sep 2019, på kl 11:34, Jan Kiszka jan.kis...@siemens.com skrev:
> On 16.09.19 09:32, Per Oberg via Xenomai wrote: > > Hello list >> I am trying to understand how rtdm works, and possibly why out of a >> historical >> context. Perhaps there is a good place to read up on this stuff, then please > > let me know. > > It seems like in the rtdm-api there is only open, but no open_rt or > > open_nrt. > > More specifically we have: > > - read_rt / read_nrt > > - recvmsg_rt / recvmsg_nrt > > - ioctl_rt / ioctl_nrt > > - .. etc. >> However, when studying an old xenomai2->3 ported driver it seems like there >> used >> to be open_rt and open_nrt. The problem I was having before (see my >> background >> comment below) was because the open had been mapped to the old open_nrt >> code, >> which in turned used a rt-lock, thus a mix of the two. When switching to a > > regular mutex it "worked", as in it didn't complain. >> In a short discussion Jan Kiszka gave me the impression that open could >> possibly > > end up being rt or nrt depending on situation. >> PÖ: I'm guessing that open is always non-rt and therefore a rtdm_lock should >> be > > used? ... > > JK: This depends. If the open code needs to synchronize only with other > > non-RT > > JK: paths, normal Linux locks are fine. If there is the need to sync with > > the > > JK: interrupt handler or some of the _rt callbacks, rtdm_lock & Co. is > > needed. >> So, how does this work? And why was (if it was) open_nrt and open_rt >> replaced > > with a common open? > The original RTDM design was foreseeing the use case of creating and > destroying > resources like file descriptors for devices in RT context. That idea was > dropped > as also the trend for the core was clearly making this less realistic. > Therefore, we removed open/socket_rt from Xenomai 3. > If you have a driver that exploited open_rt, you need to remove all > rt-sleeping > operations from its open function. If rtdm_lock is an appropriate alternative > depends on the driver locking structure and the code run under the lock. > rtdm_lock_get makes the lock holder unpreemptible. So, if rtdm_mutex was > chosen > because of lengthy code under the lock, that would not be a good alternative. > Then we would have to discuss what exactly is run there, and why. Ok, can I read up on this somewhere? I found [1], is that still valid in this context? ( Oh, and can we expect a third edition perhaps ? =) ) [1] Building Embedded Linux Systems: Concepts, Techniques, Tricks, and Traps 2nd Edition, Kindle Edition > > Background > > ---------------- >> I recently wrote about a driver which warned about "drvlib.c:1349 >> rtdm_mutex_timedlock". I got good answers which led me to some more general >> questions, but instead of continuing in the old tread I thought it better to >> start a new one since it's not about the initial problem. The driver in case >> is > > the Peak Linux Driver for their CAN hardware, see [1] > > [1] https://www.peak-system.com/fileadmin/media/linux/index.htm > Did you inform them about their problem already? Maybe they are willing to > fix > it. We can't, it's not upstream code. No, I haven't, but I will. The reason I haven't yet is because I was under the impression that this didn't happen to them. I'm trying to compile everything (driver, lib, and application) in a Yocto based SDK setup and it seems like compilation flags and environment variables are getting squashed in interesting ways. My reasoning so far was that I got this wrong somehow. Then there's the fact that making it work is only part of the goal. I do really want to understand how this fits together. > Jan > -- > Siemens AG, Corporate Technology, CT RDA IOT SES-DE > Corporate Competence Center Embedded Linux Thanks Per Öberg
