linux-kernel - Re: [RFC][RFT][PATCH] ACPI: Protection from suspending in the middle of EC transaction

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Date:	Sun, 31 Jan 2010 22:41:40 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Len Brown <lenb@...nel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][RFT][PATCH] ACPI: Protection from suspending in the
 middle of EC transaction

On Sun, 2010-01-31 at 00:29 +0100, Rafael J. Wysocki wrote: 
> Hi,
> 
> While Maxim is testing if the patch below helps with
> http://bugzilla.kernel.org/show_bug.cgi?id=14668
> I think it's necessary anyway.
> 
> The problem is that currently there's nothing to prevent us from suspending in
> the middle of an EC transaction in progress, at least as far as I can see.
> As a result, we can suspend with the ACPI global lock held or something like
> this, which leads to problems especially for hibernation (if the resume kernel
> passes control to the image kernel in the middle of an EC transaction, things
> aren't nice).  For this reason I think we should wait until there are no EC
> transactions in progress before we suspend and we should prevent any new
> EC transactions from starting after that point.  The patch below does that.
> 
> However, it does that in the EC's suspend callback, which may be too early,
> because there still is _PTS to run, so it might be necessary to do that later.
> On the other hand, the mechanics behind the ACPI global lock, which is
> acquired in acpi_ec_transaction(), requires that interrupts work, because
> otherwise there may be a problem if the global lock is not actually acquired
> after ACPI_ACQUIRE_GLOBAL_LOCK(), so the last place in which to
> wait for EC transactions to complete seems to be the platform suspend
> .prepare() callback.  Unfortunately, it's not implemented at the moment for
> ACPI and it doesn't have a hibernate counterpart and that's why I'd rather use
> the patch below, unless it's known to break things for someone.  So, if you
> can, please test it and tell me if you have any problems with it.
> 
> Of course, comments are welcome as well.
> 
> Thanks,
> Rafael
> 
> ---
>  drivers/acpi/ec.c |   17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/acpi/ec.c
> ===================================================================
> --- linux-2.6.orig/drivers/acpi/ec.c
> +++ linux-2.6/drivers/acpi/ec.c
> @@ -76,8 +76,9 @@ enum ec_command {
>  enum {
>  	EC_FLAGS_QUERY_PENDING,		/* Query is pending */
>  	EC_FLAGS_GPE_STORM,		/* GPE storm detected */
> -	EC_FLAGS_HANDLERS_INSTALLED	/* Handlers for GPE and
> +	EC_FLAGS_HANDLERS_INSTALLED,	/* Handlers for GPE and
>  					 * OpReg are installed */
> +	EC_FLAGS_SUSPENDED,		/* Driver is suspended */
>  };
>  
>  /* If we find an EC via the ECDT, we need to keep a ptr to its context */
> @@ -291,6 +292,10 @@ static int acpi_ec_transaction(struct ac
>  	if (t->rdata)
>  		memset(t->rdata, 0, t->rlen);
>  	mutex_lock(&ec->lock);
> +	if (test_bit(EC_FLAGS_SUSPENDED, &ec->flags)) {
> +		status = -EBUSY;
> +		goto unlock;
> +	}
>  	if (ec->global_lock) {
>  		status = acpi_acquire_global_lock(ACPI_EC_UDELAY_GLK, &glk);
>  		if (ACPI_FAILURE(status)) {
> @@ -1059,16 +1064,26 @@ error:
>  static int acpi_ec_suspend(struct acpi_device *device, pm_message_t state)
>  {
>  	struct acpi_ec *ec = acpi_driver_data(device);
> +
> +	mutex_lock(&ec->lock);
> +	/* Prevent transactions from happening while suspended */
> +	set_bit(EC_FLAGS_SUSPENDED, &ec->flags);
>  	/* Stop using GPE */
>  	acpi_disable_gpe(NULL, ec->gpe);
> +	mutex_unlock(&ec->lock);
>  	return 0;
>  }
>  
>  static int acpi_ec_resume(struct acpi_device *device)
>  {
>  	struct acpi_ec *ec = acpi_driver_data(device);
> +
> +	mutex_lock(&ec->lock);
>  	/* Enable use of GPE back */
>  	acpi_enable_gpe(NULL, ec->gpe);
> +	/* Allow transactions to happen again */
> +	set_bit(EC_FLAGS_SUSPENDED, &ec->flags);
          ^^^^^^^^^^^^
Thats why it doesn't work here....
Will retest now.

> +	mutex_unlock(&ec->lock);
>  	return 0;
>  }
>  
> --
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