On Mon, 19 Nov 2018 12:35:42 +0000 vitor <vitor.soares@xxxxxxxxxxxx> wrote: > Hi Boris, > > On 16/11/18 13:16, Boris Brezillon wrote: > > 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? > > > Usually the devices that I test aren't the final product so it isn't > easy to do the upstream. > > But when possible I plan to do that. > > > > > >> 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? > > I think that was for v6 I started to something to expose the bus like in > i2c-dev, but I liked the idea of expose only the device doesn't have a > driver. Do you know if there is already something in the kernel doing > the same? I know [1], but there might be other subsystems doing the same thing. [1]https://elixir.bootlin.com/linux/v4.20-rc3/source/drivers/spi/spidev.c
