Re: [PATCH] acpi: Avoid dropping rapid hotkey events (or other GPEs)on Asus EeePC

[Alan Jenkins]

[Dupe apology: CC'd to stable@xxxxxxxxxx, with the right address this time]

Andrew Morton wrote:
> On Wed, 13 Aug 2008 11:21:10 +0100 Alan Jenkins <alan-jenkins@xxxxxxxxxxxxxx> wrote:
>
>   
>> Andrew Morton wrote:
>>     
>>> Did this get fixed yet?
>>>
>>> I have an patch in -mm which I just restored (I had to tempdrop it
>>> because the acpi tree was busted for some time).  But it seems to be
>>> old.
>>>
>>> http://bugzilla.kernel.org/show_bug.cgi?id=10919 is marked "resolved"
>>> but the reporter (Maximilian) seems to think otherwise.  2.6.26.x is,
>>> afaik, still unfixed, as is 2.6.27-rc.
>>>   
>>>       
>> That's correct.  I think this specific patch should go in 2.6.27 and
>> 2.6.26-stable.  No objections have been raised so far.
>>
>> I still need this patch to make my brightness and volume control keys
>> usable in 2.6.27-rc3.  (They auto-repeat fast enough to trigger the
>> bug).  This is true even after applying the latest patches from bug
>> 10919 (#25 + #27).
>>
>>     
>
> Confusing.  Please send the patch which you think we should apply.
>
>   
>> I think the 10919 fix makes it harder to reproduce, but it definitely
>> still happens.  I guess this is because the polling-driven EC
>> transactions add 1ms delays between each byte.  The slower timings leave
>> a window where the buggy behaviour of my EC can make a difference.  (It
>> has been seen to clear the "pending event" bit after a single event is
>> read, despite having more events pending).
>>
>> There are more serious consequences of this bug.  After a while it can
>> confuse the EC enough to cause lockups or reboots during boot, or after
>> pressing a single hotkey.  This bad state is preserved over reboots,
>> even into known good kernels.  Fortunately the badness clears when power
>> is removed for a long enough period.  For a while I was worried that
>> something had physically burnt out.
>>     
>
> Oh gad.  And there's no workaround?
>
Sorry, that was confusing.

The patch in currently in -mm _is_ the workaround for this damage.  It
was not initially obvious just how important it was :-).  I've
re-attached it as requested.

10919, "laggy hotkeys" is just what it says; ACPI EC events are slower
because of polling.  It appears to be a more cosmetic issue which is
orthogonal to the _dropping_ of events.

Thanks
Alan

> --- Begin Message ---
> It looks like this EC clears the SMI_EVT bit after every query, even if there
> are more events pending.  The workaround is to repeatedly query the EC until
> it reports that no events remain.
>
> This fixes a regression in 2.6.26 (from 2.6.25.3).  Initially reported as
> "Asus Eee PC hotkeys stop working if pressed quickly" in bugzilla
> <http://bugzilla.kernel.org/show_bug.cgi?id=11089>.
>
> The regression was caused by a recently added check for interrupt storms.
> The Eee PC triggers this check and switches to polling.  When multiple events
> arrive between polling intervals, only one is fetched from the EC.  This causes
> erroneous behaviour; ultimately events stop being delivered altogether when the
> EC buffer overflows.
>
> Signed-off-by: Alan Jenkins <alan-jenkins@xxxxxxxxxxxxxx>
>
> ---
> diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
> index 5622aee..2b4c5a2 100644
> --- a/drivers/acpi/ec.c
> +++ b/drivers/acpi/ec.c
> @@ -459,14 +459,10 @@ void acpi_ec_remove_query_handler(struct acpi_ec *ec, u8 query_bit)
>  
>  EXPORT_SYMBOL_GPL(acpi_ec_remove_query_handler);
>  
> -static void acpi_ec_gpe_query(void *ec_cxt)
> +static void acpi_ec_gpe_run_handler(struct acpi_ec *ec, u8 value)
>  {
> -	struct acpi_ec *ec = ec_cxt;
> -	u8 value = 0;
>  	struct acpi_ec_query_handler *handler, copy;
>  
> -	if (!ec || acpi_ec_query(ec, &value))
> -		return;
>  	mutex_lock(&ec->lock);
>  	list_for_each_entry(handler, &ec->list, node) {
>  		if (value == handler->query_bit) {
> @@ -484,6 +480,18 @@ static void acpi_ec_gpe_query(void *ec_cxt)
>  	mutex_unlock(&ec->lock);
>  }
>  
> +static void acpi_ec_gpe_query(void *ec_cxt)
> +{
> +	struct acpi_ec *ec = ec_cxt;
> +	u8 value = 0;
> +
> +	if (!ec)
> +		return;
> +
> +	while (!acpi_ec_query(ec, &value))
> +		acpi_ec_gpe_run_handler(ec, value);
> +}
> +
>  static u32 acpi_ec_gpe_handler(void *data)
>  {
>  	acpi_status status = AE_OK;
>
>
>
>
> --- End Message ---