On Tue, Apr 6, 2021 at 4:39 PM Corey Minyard <miny...@acm.org> wrote: > > On Tue, Apr 06, 2021 at 03:21:18PM -0700, Patrick Venture wrote: > > On Tue, Apr 6, 2021 at 11:36 AM Corey Minyard <miny...@acm.org> wrote: > > > > > > On Tue, Apr 06, 2021 at 08:55:14AM -0700, Patrick Venture wrote: > > > > On Tue, Apr 6, 2021 at 8:41 AM Patrick Venture <vent...@google.com> > > > > wrote: > > > > > > > > > > On Mon, Apr 5, 2021 at 12:58 PM Corey Minyard <cminy...@mvista.com> > > > > > wrote: > > > > > > > > > > > > On Sat, Apr 03, 2021 at 03:28:08PM -0700, Patrick Venture wrote: > > > > > > > The i2c mux device pca954x implements two devices: > > > > > > > - the pca9546 and pca9548. > > > > > > > > > > > > > > Patrick Venture (2): > > > > > > > hw/i2c/core: add reachable state boolean > > > > > > > hw/i2c: add pca954x i2c-mux switch > > > > > > > > > > > > Looking this over, the code looks good, but I have a few general > > > > > > questions: > > > > > > > > > > > > * Can you register the same slave address on different channels? > > > > > > That's > > > > > > something you could do with real hardware and might be required at > > > > > > some time. It looks like to me that you can't with this patch > > > > > > set, > > > > > > but maybe I'm missing something. > > > > > > > > > > If I understand the hardware's implementation properly you can have > > > > > collisions, and this allows for collisions. I'm not sure what you > > > > > mean by having both accessible. For instance, on hardware you can > > > > > have a switch with N channels, and on two of the channels there is an > > > > > eeprom at 50. But you're unable to talk to both eeproms at the same > > > > > time, because the addresses collide -- so how would the hardware know > > > > > which you're talking to? My understanding of the behavior in this > > > > > collision case is that it just talks to the first one that responds > > > > > and can lead to unexpected things. > > > > > > > > > > There is a board, the quanta-q71l where we had to set the > > > > > idle-disconnect because there were two muxes on the same bus, with > > > > > conflicting addresses, and so we had to use idle disconnect explicitly > > > > > to make the software happy talking to the hardware -- not ideal as > > > > > having two devices behind different channels, but ultimately it's the > > > > > same idea because the devices are conflicting. > > > > > > > > > > > > > > > > > * Can you add devices to the secondary I2C busses on the mux using > > > > > > the > > > > > > standard QEMU device model, or is the function call required? > > > > > > > > > > I added the function call because I didn't see a clean way to bridge > > > > > the issue as well as, the quasi-arbitrary bus numbering used by the > > > > > kernel isn't how the hardware truly behaves, and my goal was to > > > > > implement closer to the hardware. I thought about adding an I2cBus to > > > > > the device and then you'd be able to access it, but wasn't sure of a > > > > > nice clean way to plumb that through -- I considered adding/removing > > > > > devices from the parent i2c bus instead of the boolean reachable, but > > > > > that seemed way less clean - although do-able. > > > > > > > > > > > > > > > > > I ask because I did a pca9540 and pca9541 device, but I've never > > > > > > submitted it because I didn't think it would ever be needed. It > > > > > > takes a > > > > > > different tack on the problem; it creates the secondary busses as > > > > > > standard QEMU I2C busses and bridges them. You can see it at > > > > > > > > > > > > github.com:cminyard/qemu.git master-i2c-rebase > > > > > > > > > > > > > > > > I'll have to take a look at your approach, but the idea that it > > > > > wouldn't be needed sounds bizarre to me as nearly all BMC-based qemu > > > > > boards leverage i2c muxes to handle their PCIe slot i2c routing. > > > > > > > > > > > If you design can do the things I ask, then it's better. If not, > > > > > > then > > > > > > I'm not sure. > > > > > > > > Corey, > > > > > > > > looking at your design, I should be able to do something similar with > > > > a small tweak. > > > > > > > > I think my design follows the hardware where there can be conflicts, > > > > etc, but what I didn't know how to do was add the faux I2cBuses in a > > > > useful way -- but if I add the I2cBuses to the device, and then on > > > > add/remove it registers the device on the parent bus -- i can still > > > > use the reachable boolean to control whether it's present. The faux > > > > I2cBuses would be a simplification for adding/removing i2c devices -- > > > > and would act as the device list in my object. So then setting the > > > > channels would change to walking the devices held by the bus that > > > > corresponds with the bit -- but _still_ using the reachable boolean. > > > > > > > > If you'd like, I can update my patchset to use an i2cbus for the > > > > purpose above, then it would satisfy the requirement of leveraging the > > > > normal device process and no longer require the special function call. > > > > > > That sounds reasonable. Your implementation is quite a bit simpler than > > > mine, which is a bonus. > > > > Corey; > > > > I will send out the updated patches tomorrow, but I had to cherry-pick > > your patch: > > https://github.com/cminyard/qemu/commit/c7f696d09af2d55f221a5c22900c8f71bc2244be > > so that I can get the callbacks for the bus actions, in this case, did > > you want to send that patch to the mailing list ahead? Otherwise, > > I'll try to incorporate it as a predecessor patch. > > Go ahead and incorporate it in your set so the reviewers can see why > it's necessary. > > It would also be possible to do this by modifying the i2c bus code, but > I'm not sure what the maintainers there would like.
Corey; Just wanted to give you an update. I reworked everything but wasn't super happy with the outcome, so I had a quick discussion and came up with what I think will be clean and make everybody happy. The rework is sufficiently time consuming that I don't think it'll be ready until tomorrow. > > -corey > > > > > Patrick > > > > > > > > -corey > > > > > > > > > > > Patrick > > > > > > > > > > > > > > > > -corey > > > > > > > > > > > > > > > > > > > > MAINTAINERS | 6 + > > > > > > > hw/i2c/Kconfig | 4 + > > > > > > > hw/i2c/core.c | 6 + > > > > > > > hw/i2c/i2c_mux_pca954x.c | 182 > > > > > > > +++++++++++++++++++++++++++++++ > > > > > > > hw/i2c/meson.build | 1 + > > > > > > > hw/i2c/trace-events | 5 + > > > > > > > include/hw/i2c/i2c.h | 3 + > > > > > > > include/hw/i2c/i2c_mux_pca954x.h | 60 ++++++++++ > > > > > > > 8 files changed, 267 insertions(+) > > > > > > > create mode 100644 hw/i2c/i2c_mux_pca954x.c > > > > > > > create mode 100644 include/hw/i2c/i2c_mux_pca954x.h > > > > > > > > > > > > > > -- > > > > > > > 2.31.0.208.g409f899ff0-goog > > > > > > > > > > >
