Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> >
> > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > the following lock sequences:
> > >
> > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > >
> > > The actual dependency chains are much longer. The shortened version
> > > looks somewhat like:
> > >
> > > 1. cros-ec-rpmsg on mtk-scp
> > >    ec_dev->lock -> prepare_lock
> > > 2. In rt5682_i2c_probe() on native I2C bus:
> > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > 3. In rt5682_i2c_probe() on native I2C bus:
> > >    regmap->lock -> i2c_adapter->bus_lock
> > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > >    i2c_adapter->bus_lock -> ec_dev->lock
> > >
> > > While lockdep is correct that the shared lockdep classes have a circular
> > > dependency, it is bogus because
> > >
> > >   a) 2+3 happen on a native I2C bus
> > >   b) 4 happens on the actual EC on ChromeOS devices
> > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > >      happen to expose a cros-ec interface, but do not have a passthrough
> > >      I2C bus
> > >
> > > In short, the "dependencies" are actually on different devices.
> >
> > Path of 4 looks weird to me.
> >
> > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> 
> sbs_probe() calls sbs_get_battery_presence_and_health(), which
> 
>   -> does an I2C transfer. This SBS instance is connected on the I2C bus
>      on the EC, so the I2C transfer
> 
>      -> acquires i2c_adapter->bus_lock, and

I see.

Another question: the i2c_adapter here should be different from the native
I2C bus in 2 and 3.  Did they really form the circular dependencies?