Re: [PATCH v2 0/4] hw/i2c: Adds pca954x i2c mux switch device

[Patrick Venture]

On Fri, Apr 9, 2021 at 11:31 AM Corey Minyard <cminyard@mvista.com> wrote:
>
> On Fri, Apr 09, 2021 at 09:25:41AM -0700, Patrick Venture wrote:
> > The i2c mux device pca954x implements two devices:
> >  - the pca9546 and pca9548.
> >
> > v2:
> >  - the core i2c bus now calls a match method on each i2c child, which
> >  by default will only check for a match against itself.
> >  - the pca954x device overrides the i2c device match method to search
> >  the children for each of its buses that are active.
> >  - the pca954x device now owns an i2c bus for each channel, allowing
> >  the normal device model to attach devices to the channels.
>
> I like this design.  Avoiding hacking into the bus code is a bonus.
>
> Can these devices really have multiple channels enabled at the same
> time?  That seems strange, but I guess that could be useful.

I believe I saw that in the datasheet, and it seems reasonable that
someone might want to do that.

>
> I'm not sure if you need to add a vmstate structure for this.  In
> general most new devices have them; if it's ever included on an x86
> system (or a system with vmstate transfer capability, probably more than
> x86) that will become an issue.  I'm not sure what the expectations are,
> though.

I am perfectly willing to add the vmstate structure in a future
patchset.  My team is actively developing Qemu now for BMC automated
testing support, and we will be adding other pca mux configurations,
and other support, so this will be active.  I don't anticipate a host
system including this device yet, but that's a consideration I had not
considered.

>
> -corey
>
> >
> > Patrick Venture (4):
> >   hw/i2c: name I2CNode list in I2CBus
> >   hw/i2c: add match method for device search
> >   hw/i2c: move search to i2c_scan_bus method
> >   hw/i2c: add pca954x i2c-mux switch
> >
> >  MAINTAINERS                      |   6 +
> >  hw/i2c/Kconfig                   |   4 +
> >  hw/i2c/core.c                    |  55 ++++--
> >  hw/i2c/i2c_mux_pca954x.c         | 290 +++++++++++++++++++++++++++++++
> >  hw/i2c/meson.build               |   1 +
> >  hw/i2c/trace-events              |   5 +
> >  include/hw/i2c/i2c.h             |  16 +-
> >  include/hw/i2c/i2c_mux_pca954x.h |  19 ++
> >  8 files changed, 382 insertions(+), 14 deletions(-)
> >  create mode 100644 hw/i2c/i2c_mux_pca954x.c
> >  create mode 100644 include/hw/i2c/i2c_mux_pca954x.h
> >
> > --
> > 2.31.1.295.g9ea45b61b8-goog
> >