On Tue, Oct 8, 2013 at 4:44 PM, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Tue, Oct 08, 2013 at 12:00:14PM -0500, Alan Tull wrote: >> On Fri, 2013-10-04 at 16:33 -0700, Greg Kroah-Hartman wrote: >> > On Fri, Oct 04, 2013 at 11:12:13AM -0700, H. Peter Anvin wrote: >> > > On 10/04/2013 10:44 AM, Michal Simek wrote: >> > > > >> > > > If you look at it in general I believe that there is wide range of >> > > > applications which just contain one bitstream per fpga and the >> > > > bitstream is replaced by newer version in upgrade. For them >> > > > firmware interface should be pretty useful. Just setup firmware >> > > > name with bitstream and it will be automatically loaded in startup >> > > > phase. >> > > > >> > > > Then there is another set of applications especially in connection >> > > > to partial reconfiguration where this can be done statically by >> > > > pregenerated partial bitstreams or automatically generated on >> > > > target cpu. For doing everything on the target firmware interface >> > > > is not the best because everything can be handled by user >> > > > application and it is easier just to push this bitstream to do >> > > > device and not to save it to the fs. >> > > > >> > > > I think the question here is if this subsystem could have several >> > > > interfaces. For example Alan is asking for adding char support. >> > > > Does it even make sense to have more interfaces with the same >> > > > backend driver? When this is answered then we can talk which one >> > > > make sense to have. In v2 is sysfs and firmware one. Adding char >> > > > is also easy to do. >> > > > >> > > >> > > Greg, what do you think? >> > > >> > > I agree that the firmware interface makes sense when the use of the >> > > FPGA is an implementation detail in a fixed hardware configuration, >> > > but that is a fairly restricted use case all things considered. >> > >> > Ideally I thought this would be just like "firmware", you dump the file >> > to the FPGA, it validates it and away you go with a new image running in >> > the chip. >> > >> > But, it sounds like this is much more complicated, so much so that >> > configfs might be the correct interface for it, as you can do lots of >> > things there, and it is very flexible (some say too flexible...) >> > >> > A char device, with a zillion different custom ioctls is also a way to >> > do it, but one that I really want to avoid as that gets messy really >> > quickly. >> >> Hi Greg, >> >> We are discussing a char device that has very few interfaces: >> - a way of writing the image to fpga >> - a way of getting fpga manager status >> - a way of setting fpga manager state >> >> This all looks like standard char driver interface to me. Writing the >> image could be writing to the devnode (cat image.bin > /dev/fpga0). The >> status stuff would be sysfs attributes. All normal stuff any char >> driver in the kernel would do. Why not just go with that? > > Because we really hate to add new ioctls to the kernel if at all > possible. I don't see any need for adding any ioctls. > Using sysfs (and it's one-value-per-file rule), makes > userspace tools easier, and managing the different devices in the system > easier (you know _exactly_ which device you are talking to, you don't > have to guess based on minor number). That's cool. The interface we could use is writing the raw fpga data to /sys/class/fpga_manager/fpga0/fpga_config_data Reading or setting the fpga state could be from /sys/class/fpga_manager/fpga0/fpga_config_state Or do I misunderstand? Do you include sysfs attributes when you are talking about ioctls? Alan > > thanks, > > greg k-h > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
