On Fri, 16 Nov 2018 12:31:42 +0000 vitor <vitor.soares@xxxxxxxxxxxx> wrote: > Hi Boris, > > > On 15/11/18 19:00, Boris Brezillon wrote: > > On Thu, 15 Nov 2018 18:03:47 +0000 > > vitor <vitor.soares@xxxxxxxxxxxx> wrote: > > > >> Hi Boris, > >> > >> > >> On 15/11/18 15:28, Boris Brezillon wrote: > >>> On Thu, 15 Nov 2018 16:01:37 +0100 > >>> Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote: > >>> > >>>> Hi Boris, > >>>> > >>>>> What we could do though, is expose I3C devices that do not have a > >>>>> driver in kernel space, like spidev does. > >>>> ... > >>>> > >>>>> Mark, Wolfram, Arnd, Greg, any opinion? > >>>> Is there a benefit for having drivers in userspace? My gut feeling is to > >>>> encourage people to write kernel drivers. If this is, for some reason, > >>>> not possible for some driver, then we have a use case at hand to test > >>>> the then-to-be-developed userspace interface against. Until then, I > >>>> personally wouldn't waste effort on designing it without a user in > >>>> sight. > >>> I kind of agree with that. Vitor, do you have a use case in mind for > >>> such userspace drivers? I don't think it's worth designing an API for > >>> something we don't need (yet). > >> My use case is a tool for tests, lets say like the i2c tools. > > What would you like to test exactly? > > > >> There is > >> other subsystems, some of them mentioned on this thread, that have and > >> ioctl system call or other method to change parameters or send data. > > I don't think they added the /dev interface before having a real use > > case for it. > > > >> > >> I rise this topic because I really think it worth to define now how this > >> should be design (and for me how to do the things right) to avoid future > >> issues. > > Actually it should be done the other way around: you should have a real > > need and the /dev interface should be designed to fulfill this need. > > Based on this real use case we can discuss other potential usage that > > might appear in the future and try to design something more > > future-proof, but clearly, this userspace interface should be driven by > > a real/well-defined use case. > > > > Also, exposing things to userspace is way more risky than adding a new > > in-kernel subsystem/framework, because it then becomes part of the > > stable ABI. > > > > To make things clearer, I'm not against the idea of exposing I3C > > devices (or I3C buses) to userspace, but I'd like to understand what you > > plan to do with that. If this is about testing, what kind of tests > > you'd like to run. If this is about developing drivers in userspace, > > why can't these be done in kernel space (license issues?), and what > > would those drivers be allowed to do? > > > Basically I need a tool that help me during the development and to avoid > me to write a dummy driver for each device that I test. But we want I3C device drivers to be upstreamed, so why not developing a real driver everytime you test a new device and submitting it upstream? > > For instances do some read/write, Doing SDR/DDR transfers is probably acceptable, but I still think we should push hard to have kernel drivers when that's possible. > get/set ccc commands, Exposing CCC commands is definitely not a good idea, since they're not even exposed to kernel drivers. > if something > goes wrong during the bus initialization have a to debug etc... Can't we add such a debug infrastructure in the kernel. Maybe we can expose debugfs files too if that helps, though if those debugfs files are actually used by userspace libs/tools, it's not any better than ioctls or sysfs files, since they will anyway become a stable ABI. > > > For me this is a valid use case and I imagine when people start to > develop in i3c this interface will help everyone. How about you propose an i3cdev driver that allow users to do SDR transfers throuh an ioctl?
