Date:	Thu, 27 Feb 2014 00:45:55 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Kieran Clancy <clancy.kieran@...il.com>
Cc:	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lan Tianyu <tianyu.lan@...el.com>,
	Juan Manuel Cabo <juanmanuel.cabo@...il.com>,
	Dennis Jansen <dennis.jansen@....de>
Subject: Re: [PATCH] ACPI / EC: Clear stale EC events on Samsung systems

On Thursday, February 27, 2014 02:12:40 AM Kieran Clancy wrote:
> A number of Samsung notebooks (530Uxx/535Uxx/540Uxx/550Pxx/900Xxx/etc)
> continue to log events during sleep (lid open/close, AC plug/unplug,
> battery level change), which accumulate in the EC until a buffer fills.
> After the buffer is full (tests suggest it holds 8 events), GPEs stop
> being triggered for new events. This state persists on wake or even on
> power cycle, and prevents new events from being registered until the EC
> is manually polled.
> 
> This is the root cause of a number of bugs, including AC not being
> detected properly, lid close not triggering suspend, and low ambient
> light not triggering the keyboard backlight. The bug also seemed to be
> responsible for performance issues on at least one user's machine.
> 
> Juan Manuel Cabo found the cause of bug and the workaround of polling
> the EC manually on wake.
> 
> This patch:
> - Adds a function acpi_ec_clear() which polls the EC, at most
>   ACPI_EC_CLEAR_MAX (currently 20) times. A warning is logged if this
>   limit is reached.
> - Adds a flag EC_FLAGS_CLEAR_ON_RESUME which is set to 1 if the DMI
>   system vendor is Samsung. This check could be replaced by several more
>   specific DMI vendor/product pairs, but it's likely that the bug
>   affects more Samsung products than just the five series mentioned
>   above. Further, it should not be harmful to run acpi_ec_clear() on
>   systems without the bug; it will return immediately after finding no
>   data waiting.
> - Runs acpi_ec_clear() on initialisation (boot), from acpi_ec_add()
> - Runs acpi_ec_clear() on wake, from acpi_ec_unblock_transactions()
> 
> References: https://bugzilla.kernel.org/show_bug.cgi?id=44161
> References: https://bugzilla.kernel.org/show_bug.cgi?id=45461
> References: https://bugzilla.kernel.org/show_bug.cgi?id=57271
> Signed-off-by: Kieran Clancy <clancy.kieran@...il.com>
> Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
> Signed-off-by: Juan Manuel Cabo <juanmanuel.cabo@...il.com>
> Signed-off-by: Dennis Jansen <dennis.jansen@....de>

There are too many sign-offs under this patch.  I suppose some of them
should be Acked-by or Reviewed-by.

Are you the author?

> Tested-by: Maurizio D'Addona <mauritiusdadd@...il.com>
> Tested-by: San Zamoyski <san@...snet.pl>
> ---
>  drivers/acpi/ec.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
> index 959d41a..f437d9a 100644
> --- a/drivers/acpi/ec.c
> +++ b/drivers/acpi/ec.c
> @@ -67,6 +67,8 @@ enum ec_command {
>  #define ACPI_EC_DELAY		500	/* Wait 500ms max. during EC ops */
>  #define ACPI_EC_UDELAY_GLK	1000	/* Wait 1ms max. to get global lock */
>  #define ACPI_EC_MSI_UDELAY	550	/* Wait 550us for MSI EC */
> +#define ACPI_EC_CLEAR_MAX	20	/* Maximum number of events to query
> +					 * when trying to clear the EC */
>  
>  enum {
>  	EC_FLAGS_QUERY_PENDING,		/* Query is pending */
> @@ -116,6 +118,7 @@ EXPORT_SYMBOL(first_ec);
>  static int EC_FLAGS_MSI; /* Out-of-spec MSI controller */
>  static int EC_FLAGS_VALIDATE_ECDT; /* ASUStec ECDTs need to be validated */
>  static int EC_FLAGS_SKIP_DSDT_SCAN; /* Not all BIOS survive early DSDT scan */
> +static int EC_FLAGS_CLEAR_ON_RESUME; /* EC should be polled on boot/resume */
>  
>  /* --------------------------------------------------------------------------
>                               Transaction Management
> @@ -440,6 +443,26 @@ acpi_handle ec_get_handle(void)
>  
>  EXPORT_SYMBOL(ec_get_handle);
>  
> +static int acpi_ec_query_unlocked(struct acpi_ec *ec, u8 *data);
> +
> +/* run with locked ec mutex */
> +static void acpi_ec_clear(struct acpi_ec *ec)
> +{
> +	int i, status;
> +	u8 value = 0;
> +
> +	for (i = 0; i < ACPI_EC_CLEAR_MAX; i++) {
> +		status = acpi_ec_query_unlocked(ec, &value);
> +		if (status || !value)
> +			break;
> +	}
> +
> +	if (i == ACPI_EC_CLEAR_MAX)
> +		pr_warn("Warning: Maximum of %d stale EC events cleared\n", i);
> +	else
> +		pr_info("%d stale EC events cleared\n", i);
> +}
> +
>  void acpi_ec_block_transactions(void)
>  {
>  	struct acpi_ec *ec = first_ec;
> @@ -463,6 +486,10 @@ void acpi_ec_unblock_transactions(void)
>  	mutex_lock(&ec->mutex);
>  	/* Allow transactions to be carried out again */
>  	clear_bit(EC_FLAGS_BLOCKED, &ec->flags);
> +
> +	if (EC_FLAGS_CLEAR_ON_RESUME)
> +		acpi_ec_clear(ec);
> +
>  	mutex_unlock(&ec->mutex);
>  }
>  
> @@ -821,6 +848,13 @@ static int acpi_ec_add(struct acpi_device *device)
>  
>  	/* EC is fully operational, allow queries */
>  	clear_bit(EC_FLAGS_QUERY_PENDING, &ec->flags);
> +
> +	/* Some hardware may need the EC to be cleared before use */
> +	if (EC_FLAGS_CLEAR_ON_RESUME) {
> +		mutex_lock(&ec->mutex);
> +		acpi_ec_clear(ec);
> +		mutex_unlock(&ec->mutex);
> +	}
>  	return ret;
>  }
>  
> @@ -922,6 +956,30 @@ static int ec_enlarge_storm_threshold(const struct dmi_system_id *id)
>  	return 0;
>  }
>  
> +/*
> + * On some hardware it is necessary to clear events accumulated by the EC during
> + * sleep. These ECs stop reporting GPEs until they are manually polled, if too
> + * many events are accumulated. (e.g. Samsung Series 5/9 notebooks)
> + *
> + * https://bugzilla.kernel.org/show_bug.cgi?id=44161
> + *
> + * Ideally, the EC should also be instructed not to accumulate events during
> + * sleep (which Windows seems to do somehow), but the interface to control this
> + * behaviour is not known at this time.
> + *
> + * Models known to be affected are Samsung 530Uxx/535Uxx/540Uxx/550Pxx/900Xxx,
> + * however it is very likely that other Samsung models are affected.
> + *
> + * On systems which don't accumulate EC events during sleep, this extra check
> + * should be harmless.
> + */
> +static int ec_clear_on_resume(const struct dmi_system_id *id)
> +{
> +	pr_debug("Detected system needing EC poll on resume.\n");
> +	EC_FLAGS_CLEAR_ON_RESUME = 1;
> +	return 0;
> +}
> +
>  static struct dmi_system_id ec_dmi_table[] __initdata = {
>  	{
>  	ec_skip_dsdt_scan, "Compal JFL92", {
> @@ -965,6 +1023,9 @@ static struct dmi_system_id ec_dmi_table[] __initdata = {
>  	ec_validate_ecdt, "ASUS hardware", {
>  	DMI_MATCH(DMI_SYS_VENDOR, "ASUSTek Computer Inc."),
>  	DMI_MATCH(DMI_PRODUCT_NAME, "L4R"),}, NULL},
> +	{
> +	ec_clear_on_resume, "Samsung hardware", {
> +	DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD.")}, NULL},
>  	{},
>  };
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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