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From:   Guenter Roeck <groeck@google.com>
Date:   Thu, 7 Apr 2022 11:51:58 -0700
Message-ID: <CABXOdTeAN201fA5FMT1jhOmooNHmvkZPdjnwMM=5j-btovF+3Q@mail.gmail.com>
Subject: Re: [PATCH] platform/chrome: cros_ec_typec: Check for EC driver
To:     Benson Leung <bleung@google.com>
Cc:     Akihiko Odaki <akihiko.odaki@gmail.com>,
        Prashant Malani <pmalani@chromium.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        chrome-platform@lists.linux.dev,
        Benson Leung <bleung@chromium.org>,
        Guenter Roeck <groeck@chromium.org>
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On Thu, Apr 7, 2022 at 10:09 AM Benson Leung <bleung@google.com> wrote:
>
> Hi Akihiko,
>
> On Fri, Apr 08, 2022 at 02:03:52AM +0900, Akihiko Odaki wrote:
> > If I read the code correctly, the registration itself happens synchronously
> > and platform_device_register_data() always returns a non-NULL value unless
> > it returns -ENOMEM. The driver, however, can be asynchronously bound and
> > dev_get_drvdata(&typec->ec->ec->dev) can return NULL as the consequence. It
> > would have a call trace like the following when scheduling asynchronous
> > driver binding:
> > platform_device_register_data()
> > platform_device_register_resndata()
> > platform_device_register_full()
> > -  This always creates and returns platform_device.
> > platform_device_add()
> > - This adds the created platform_device.
> > device_add()
> > bus_probe_device()
> > device_initial_probe()
> > __device_attach()
> > - This schedules asynchronous probing.
> >
> > typec->ec->ec should be pointing to the correct platform_device as the
> > patched driver works without Oops on my computer. It is not NULL at least.
>
> Can you provide more information about your test computer in this case?
>
> Is it a Chromebook running stock firmware (if so, please let us know which
> model, and which firmware version it is running).
> In the past, we've also gotten some reports from people running MrChromebox
> custom firmware on older Chromebooks which have exposed other bugs in
> this driver.
>

I think we should be able to reproduce the problem by configuring
CONFIG_CROS_EC_CHARDEV=m on any Chromebook supporting Type C.

Guenter

> Let us know if that's the case here, and where we can get that firmware.
>
> Thanks,
> Benson
>
> --
> Benson Leung
> Staff Software Engineer
> Chrome OS Kernel
> Google Inc.
> bleung@google.com
> Chromium OS Project
> bleung@chromium.org