Hi Dmitry,
On Mon, Oct 28, 2024 at 2:34 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
> On Tue, Oct 22, 2024 at 07:37:01AM -0700, Doug Anderson wrote:
> > On Tue, Oct 22, 2024 at 12:12 AM Geert Uytterhoeven
> > <geert@xxxxxxxxxxxxxx> wrote:
> > > > > > > > However, using i2c_client->adapter->nr instead of ida_alloc()
> > > > > > > > in the TI driver does sound like a good idea to me...
> > > > > > >
> > > > > > > Great!
> > > > >
> > > > > > With the I2C adapter numbers, that becomes:
> > > > > >
> > > > > > /sys/bus/auxiliary/devices
> > > > > > ├── ti_sn65dsi86.gpio.1
> > > > > > ├── ti_sn65dsi86.pwm.1
> > > > > > ├── ti_sn65dsi86.aux.1
> > > > > > ├── ti_sn65dsi86.bridge.1
> > > > > > ├── ti_sn65dsi86.gpio.4
> > > > > > ├── ti_sn65dsi86.pwm.4
> > > > > > ├── ti_sn65dsi86.aux.4
> > > > > > └── ti_sn65dsi86.bridge.4
> > > > > >
> > > > > > > adapter->nr instead like other aux subsystems already do.
> > > > >
> > > > > Unfortunately the devil is in the details, as usual: there can be
> > > > > multiple instances of the sn65dsi86 bridge on a single I2C bus,
> > > > > so adapter->nr is not guaranteed to generate a unique name.
> > > >
> > > > In the case of sn65dsi86 I think we'd actually be OK. The TI bridge
> > > > chip is always at bus address 0x2d so you can't have more than one on
> > > > the same bus. Unless you added something funky atop it (like a mux of
> > > > some sort) you might be OK.
> > >
> > > It's 0x2c on mine ;-)
> > >
> > > 8.5.1 Local I2C Interface Overview
> > > The 7-bit device address for SN65DSI86 is factory preset to 010110X
> > > with the least significant bit being determined by the ADDR control
> > > input.
> >
> > Doh! I missed that in my search of the doc. I guess because they
> > decided to specify the address in binary in that part so my searching
> > for both the 7-bit and 8-bit I2C address didn't trigger. Oh well.
> >
> > > > > Changing the auxiliary bus to use the parent's name instead of the
> > > > > module name, as suggested by Laurent, would fix that.
> > > >
> > > > Right. On my system dev_name() of the sn65dsi86 device is "2-002d". If
> > > > we had a second on i2c bus 4, we'd have:
> > > >
> > > > /sys/bus/auxiliary/devices
> > > > ├── 2-002d.gpio.0
> > > > ├── 2-002d.pwm.0
> > > > ├── 2-002d.aux.0
> > > > ├── 2-002d.bridge.0
> > > > ├── 4-002d.gpio.0
> > > > ├── 4-002d.pwm.0
> > > > ├── 4-002d.aux.0
> > > > └── 4-002d.bridge.0
> > > >
> > > > ...and I think that's guaranteed to be unique because all the i2c
> > > > devices are flat in "/sys/bus/i2c/devices".
> > >
> > > Correct.
> >
> > So given everything, using the dev_name() of the "parent" sounds
> > pretty good and seems like it addresses everyone's concerns. Was there
> > a part of the conversation where someone pointed out problems with it
> > that I missed? Is the next step to post a patch implementing that?
> > It'll change sysfs paths and dev names for everyone using AUX bus, but
> > presumably that's OK?
>
> It also requires changing in the way the auxiliary_match_id() works.
> Currently matching is done using modname + ID.
Right, so just using the parent's name instead of modname won't work,
as the former is not a fixed string.
> So, maybe using MODNAME.NAME.parent-name.ID is better (e.g.
> ti_sn65dsi86.gpio.2-002d.1). It will still require changes to the
> match_id function, but they won't be that intrusive (one just has to
> skip two parts of the name instead of skipping just one).
IMHO this is becoming too complex. What if the parent's name contains
a period?
So just using ida_alloc() in the caller seems like the most
straight-forward solution.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
