On Mon, 12 Apr 2021, at 18:18, Arnd Bergmann wrote: > On Mon, Apr 12, 2021 at 3:33 AM Andrew Jeffery <andrew@xxxxxxxx> wrote: > > On Fri, 9 Apr 2021, at 17:25, Arnd Bergmann wrote: > > > On Fri, Mar 19, 2021 at 7:31 AM Andrew Jeffery <andrew@xxxxxxxx> wrote: > > > > > > > > The existing IPMI chardev encodes IPMI behaviours as the name suggests. > > > > However, KCS devices are useful beyond IPMI (or keyboards), as they > > > > provide a means to generate IRQs and exchange arbitrary data between a > > > > BMC and its host system. > > > > > > I only noticed the series after Joel asked about the DT changes on the arm > > > side. One question though: > > > > > > How does this related to the drivers/input/serio/ framework that also talks > > > to the keyboard controller for things that are not keyboards? > > > > I've taken a brief look and I feel they're somewhat closely related. > > > > It's plausible that we could wrangle the code so the Aspeed and Nuvoton > > KCS drivers move under drivers/input/serio. If you squint, the i8042 > > serio device driver has similarities with what the Aspeed and Nuvoton > > device drivers are providing to the KCS IPMI stack. > > After looking some more into it, I finally understood that the two are > rather complementary. While the drivers/char/ipmi/kcs_bmc.c > is the other (bmc) end of drivers/char/ipmi/ipmi_kcs_sm.c, it seems > that the proposed kcs_bmc_cdev_raw.c interface would be > what corresponds to the other side of > drivers/input/serio/i8042.c+userio.c. Right. I guess the question is should we be splitting kernel subsystems along host/bmc lines? Doesn't feel intuitive, it's all Linux, but maybe we can consolidate in the future if it makes sense? > Then again, these are also on > separate ports (0x60 for the keyboard controller, 0xca2 for the BMC > KCS), so they would never actually talk to one another. Well, sort of I guess. On Power systems we don't use the keyboard controller for IPMI or keyboards, so we're just kinda exploiting the hardware for our own purposes. > > > Both the KCS IPMI and raw chardev I've implemented in this patch need > > both read and write access to the status register (STR). serio could > > potentially expose its value through serio_interrupt() using the > > SERIO_OOB_DATA flag, but I haven't put any thought into it beyond this > > sentence. We'd need some extra support for writing STR via the serio > > API. I'm not sure that fits into the abstraction (unless we make > > serio_write() take a flags argument?). > > > > In that vein, the serio_raw interface is close to the functionality > > that the raw chardev provides in this patch, though again serio_raw > > lacks userspace access to STR. Flags are ignored in the ->interrupt() > > callback so all values received via ->interrupt() are exposed as data. > > The result is there's no way to take care of SERIO_OOB_DATA in the > > read() path. Given that, I think we'd have to expose an ioctl() to > > access the STR value after taking care of SERIO_OOB_DATA in > > ->interrupt(). > > > > I'm not sure where that lands us. > > Based on what I looked up, I think you can just forget about my original > question. We have two separate interfaces that use an Intel 8042-style > protocol, but they don't really interact. Right, this is still true given Power doesn't care for keyboards or IPMI via the keyboard controllers; the two still don't interact. Andrew
