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From:   Guenter Roeck <groeck@google.com>
Date:   Wed, 21 Dec 2022 12:07:06 -0800
Message-ID: <CABXOdTcHppsLTDTXBd9ikL+Hk8W4oW_NkWMhOJgmf9aDSW+FKA@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 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.

> +               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() ?

> +       }

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.

How is this handled today ? Does the EC just reset the AP ?

>  }
>
>  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
>