On Fri, Oct 27, 2023 at 01:25:56PM +0200, Krzysztof Kozlowski wrote: > On 27/10/2023 11:09, Wolfram Sang wrote: > > On Fri, Oct 27, 2023 at 04:31:03PM +1300, Chris Packham wrote: > >> Add bus-reset-gpios and bus-reset-duration-us properties to the > >> marvell,mv64xxx-i2c binding. These can be used to describe hardware > >> where a common reset GPIO is connected to all downstream devices on and > >> I2C bus. This reset will be asserted then released before the downstream > >> devices on the bus are probed. > >> > >> Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx> > >> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> > > > > Krzysztof, are you fine with this change? > > Actually no. NAK. > > Not because of the naming, but because the new name triggered some new > paths in my brain which brought the point - this is old problem of power > sequencing of children. > > I believe this must be solved in more generic way. First - generic for > all I2C devices. Second - generic also matching other buses/subsystems, > which have similar problem. We did it for USB (onboard USB), MMC > (unloved MMC power sequence) and now we are doing it for PCIe and few > others (Cc: Abel) Unlike the others I2C doesn't expect to access the bus/device before devices probe, right? > https://lpc.events/event/17/contributions/1507/ Oh, good! > Current solution is heavily limited. What about regulators? What about > buses having 2 reset lines (still the same bus)? What about sequence? A more complicated case should be handled by the device's driver. If the GPIO reset was not shared we'd be handling it there too. I think what's needed is to solve the shared aspect. That's already done with reset subsys, so I think making 'reset-gpios' handled by it too is the way forward. That would handle the QCA WiFi/BT case I think. I'm not sure waiting for that or something else to happen is worth holding up this simple case. It's not the only case of a common reset for a bus (MDIO). Rob
