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From:   Guenter Roeck <groeck@google.com>
Date:   Wed, 21 Dec 2022 16:08:40 -0800
Message-ID: <CABXOdTdKNSfEbRAjrPTrCghb05xMNLrqhTz1C+G_UCnpMBJL+A@mail.gmail.com>
Subject: Re: [PATCH] drivers/cros_ec: Handle CrOS EC panics
To:     Rob Barnes <robbarnes@google.com>
Cc:     Guenter Roeck <groeck@chromium.org>,
        chrome-platform@lists.linux.dev, linux-kernel@vger.kernel.org,
        dtor@chromium.org, Benson Leung <bleung@chromium.org>
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On Wed, Dec 21, 2022 at 3:56 PM Rob Barnes <robbarnes@google.com> wrote:
>
> On Wed, Dec 21, 2022 at 1:07 PM Guenter Roeck <groeck@google.com> wrote:
> >
> > On Wed, Dec 21, 2022 at 10:56 AM Rob Barnes <robbarnes@google.com> wrote:
> > >
> > > Add handler for CrOS EC panic events. When a panic is reported,
> > > poll EC log then force an orderly shutdown.
> > >
> > > This will preserve the EC log leading up to the crash.
> > >
> > > Signed-off-by: Rob Barnes <robbarnes@google.com>
> > > ---
> > >  drivers/platform/chrome/cros_ec_debugfs.c   | 24 +++++++++++++++++++++
> > >  drivers/platform/chrome/cros_ec_lpc.c       | 10 +++++++++
> > >  include/linux/platform_data/cros_ec_proto.h |  9 ++++++++
> > >  3 files changed, 43 insertions(+)
> > >
> > > diff --git a/drivers/platform/chrome/cros_ec_debugfs.c b/drivers/platform/chrome/cros_ec_debugfs.c
> > > index 21d973fc6be2..31637a4e4cf9 100644
> > > --- a/drivers/platform/chrome/cros_ec_debugfs.c
> > > +++ b/drivers/platform/chrome/cros_ec_debugfs.c
> > > @@ -49,6 +49,7 @@ struct cros_ec_debugfs {
> > >         struct delayed_work log_poll_work;
> > >         /* EC panicinfo */
> > >         struct debugfs_blob_wrapper panicinfo_blob;
> > > +       struct notifier_block notifier_panic;
> > >  };
> > >
> > >  /*
> > > @@ -437,6 +438,23 @@ static int cros_ec_create_panicinfo(struct cros_ec_debugfs *debug_info)
> > >         return ret;
> > >  }
> > >
> > > +static int cros_ec_debugfs_panic_event(struct notifier_block *nb,
> > > +                                      unsigned long queued_during_suspend,
> > > +                                      void *_notify)
> > > +{
> > > +       struct cros_ec_debugfs *debug_info =
> > > +               container_of(nb, struct cros_ec_debugfs, notifier_panic);
> > > +
> > > +       if (debug_info->log_buffer.buf) {
> > > +               /* Force log poll work to run immediately */
> > > +               mod_delayed_work(debug_info->log_poll_work.wq, &debug_info->log_poll_work, 0);
> > > +               /* Block until log poll work finishes */
> > > +               flush_delayed_work(&debug_info->log_poll_work);
> > > +       }
> > > +
> > > +       return NOTIFY_DONE;
> > > +}
> > > +
> > >  static int cros_ec_debugfs_probe(struct platform_device *pd)
> > >  {
> > >         struct cros_ec_dev *ec = dev_get_drvdata(pd->dev.parent);
> > > @@ -473,6 +491,12 @@ static int cros_ec_debugfs_probe(struct platform_device *pd)
> > >         debugfs_create_u16("suspend_timeout_ms", 0664, debug_info->dir,
> > >                            &ec->ec_dev->suspend_timeout_ms);
> > >
> > > +       debug_info->notifier_panic.notifier_call = cros_ec_debugfs_panic_event;
> > > +       ret = blocking_notifier_chain_register(&ec->ec_dev->panic_notifier,
> > > +                                              &debug_info->notifier_panic);
> > > +       if (ret)
> > > +               goto remove_debugfs;
> > > +
> > >         ec->debug_info = debug_info;
> > >
> > >         dev_set_drvdata(&pd->dev, ec);
> > > diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
> > > index 7fc8f82280ac..21958c3b0c28 100644
> > > --- a/drivers/platform/chrome/cros_ec_lpc.c
> > > +++ b/drivers/platform/chrome/cros_ec_lpc.c
> > > @@ -21,6 +21,7 @@
> > >  #include <linux/platform_data/cros_ec_proto.h>
> > >  #include <linux/platform_device.h>
> > >  #include <linux/printk.h>
> > > +#include <linux/reboot.h>
> > >  #include <linux/suspend.h>
> > >
> > >  #include "cros_ec.h"
> > > @@ -332,6 +333,15 @@ static void cros_ec_lpc_acpi_notify(acpi_handle device, u32 value, void *data)
> > >
> > >         if (value == ACPI_NOTIFY_DEVICE_WAKE)
> > >                 pm_system_wakeup();
> > > +
> > > +       if (value == ACPI_NOTIFY_CROS_EC_PANIC) {
> > > +               dev_err(ec_dev->dev,
> > > +                       "CrOS EC Panic Reported. Shutdown is imminent!");
> >
> > dev_emerg() would seem to be more appropriate, given that we'll be
> > crashing a second later.
>
> Makes sense. Will do.
>
> >
> > > +               blocking_notifier_call_chain(&ec_dev->panic_notifier, 0,
> > > +                                            ec_dev);
> > > +               /* Begin orderly shutdown. Force shutdown after 1 second. */
> > > +               hw_protection_shutdown("CrOS EC Panic", 1000);
> >
> > That seems to be the wrong API. From its description:
> >
> >  * Initiate an emergency system shutdown in order to protect hardware from
> >  * further damage. Usage examples include a thermal protection or a voltage or
> >  * current regulator failures.
> >
> > This is an EC crash that apparently can not be handled gracefully.
> > That has nothing to do with hardware protection. Why not just call
> > panic() ?
>
> I'm adding the ability for the EC to somewhat gracefully handle a
> class of panics. The EC will enter "system safe mode" aka limp mode.
> All tasks are disabled except for a few critical ones. The purpose of
> this mode is to give the OS a couple of seconds to extract info about
> the EC panic and shutdown as gracefully as possible. EC will still
> force a reset after 2 seconds.
>
> Since the EC is in a precarious, non deterministic state and the EC is
> at least partially responsible for thermal and power regulation, it is
> arguably a hardware protection event.
>

In my opinion it is an abuse of the API. I guess we have to agree to disagree.

Guenter

> The primary motivation for allowing the OS to attempt an orderly
> shutdown is to sync user data and EC panic data to storage. Will panic
> sync storage? Or will that need to be a seperate call?
>
> >
> > > +       }
> >
> > It troubles me that this comes last. That means the entire
> > mkbp_event_supported handling executes first. What troubles me even
> > more is that 'value' is, with the exception of
> > ACPI_NOTIFY_DEVICE_WAKE, not checked at all. Presumably the EC sends
> > some well defined value if it has an event to report. I don't think it
> > is a good idea to depend on cros_ec_get_next_event() returning
> > something useful after the EC crashed.
>
> Could certainly move the ACPI_NOTIFY_CROS_EC_PANIC to the top. I think
> 'value' will be 0x80 when there's MKBP events. I will validate this
> assumption.
>
> > How is this handled today ? Does the EC just reset the AP ?
>
> EC just immediately resets the AP and itself. System safe mode (see
> go/ec-system-safe-mode) will allow the EC to run a few seconds after
> some types of crashes.
>
>
>
> >
> > >  }
> > >
> > >  static int cros_ec_lpc_probe(struct platform_device *pdev)
> > > diff --git a/include/linux/platform_data/cros_ec_proto.h b/include/linux/platform_data/cros_ec_proto.h
> > > index e43107e0bee1..1c4487271836 100644
> > > --- a/include/linux/platform_data/cros_ec_proto.h
> > > +++ b/include/linux/platform_data/cros_ec_proto.h
> > > @@ -41,6 +41,13 @@
> > >  #define EC_MAX_REQUEST_OVERHEAD                1
> > >  #define EC_MAX_RESPONSE_OVERHEAD       32
> > >
> > > +/*
> > > + * EC panic is not covered by the standard (0-F) ACPI notify values.
> > > + * Arbitrarily choosing B0 to notify ec panic, which is in the 84-BF
> > > + * device specific ACPI notify range.
> > > + */
> > > +#define ACPI_NOTIFY_CROS_EC_PANIC      0xB0
> > > +
> > >  /*
> > >   * Command interface between EC and AP, for LPC, I2C and SPI interfaces.
> > >   */
> > > @@ -176,6 +183,8 @@ struct cros_ec_device {
> > >         /* The platform devices used by the mfd driver */
> > >         struct platform_device *ec;
> > >         struct platform_device *pd;
> > > +
> > > +       struct blocking_notifier_head panic_notifier;
> > >  };
> > >
> > >  /**
> > > --
> > > 2.39.0.314.g84b9a713c41-goog
> > >