Re: [RFC][RFT][PATCH] ACPI: Protection from suspending in themiddle of EC transaction

From: Maxim Levitsky
Date: Sun Jan 31 2010 - 15:41:52 EST


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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