[PATCH v4 5/6] ACPI / EC: Reduce ec_poll() by referencing the last register access timestamp.

Lv Zheng
2015-02-05T08:27:38Z

Timeout in the ec_poll() doesn't refer to the last register access time. It
thus can win the competition against the acpi_ec_gpe_handler() if a
transaction takes longer than 1ms but individual register accesses are less
than 1ms. In some cases, it can make the following silicon bug easier to
be triggered:
GPE EN is not wired to the GPE trigger line, so when GPE STS is already
set when 1 is written to GPE EN, no GPE can be triggered.

This patch adds register access timestamp reference support for ec_poll()
to reduce the number of ec_poll() invocations.

Reported-by: Venkat Raghavulu <venkat.raghavulu@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
---
drivers/acpi/ec.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 2540870..e000cf7 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -71,6 +71,7 @@ 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_UDELAY_POLL 1000 /* Wait 1ms for EC transaction polling */
#define ACPI_EC_CLEAR_MAX 100 /* Maximum number of events to query
* when trying to clear the EC */

@@ -118,6 +119,7 @@ struct transaction {
u8 wlen;
u8 rlen;
u8 flags;
+ unsigned long timestamp;
};

static int acpi_ec_query(struct acpi_ec *ec, u8 *data);
@@ -155,6 +157,7 @@ static inline u8 acpi_ec_read_data(struct acpi_ec *ec)
{
u8 x = inb(ec->data_addr);

+ ec->curr->timestamp = jiffies;
pr_debug("EC_DATA(R) = 0x%2.2x\n", x);
return x;
}
@@ -163,12 +166,14 @@ static inline void acpi_ec_write_cmd(struct acpi_ec *ec, u8 command)
{
pr_debug("EC_SC(W) = 0x%2.2x\n", command);
outb(command, ec->command_addr);
+ ec->curr->timestamp = jiffies;
}

static inline void acpi_ec_write_data(struct acpi_ec *ec, u8 data)
{
pr_debug("EC_DATA(W) = 0x%2.2x\n", data);
outb(data, ec->data_addr);
+ ec->curr->timestamp = jiffies;
}

#ifdef DEBUG
@@ -359,6 +364,7 @@ static void start_transaction(struct acpi_ec *ec)
{
ec->curr->irq_count = ec->curr->wi = ec->curr->ri = 0;
ec->curr->flags = 0;
+ ec->curr->timestamp = jiffies;
advance_transaction(ec);
}

@@ -370,20 +376,25 @@ static int ec_poll(struct acpi_ec *ec)
while (repeat--) {
unsigned long delay = jiffies +
msecs_to_jiffies(ec_delay);
+ unsigned long usecs = ACPI_EC_UDELAY_POLL;
do {
/* don't sleep with disabled interrupts */
if (EC_FLAGS_MSI || irqs_disabled()) {
- udelay(ACPI_EC_MSI_UDELAY);
+ usecs = ACPI_EC_MSI_UDELAY;
+ udelay(usecs);
if (ec_transaction_completed(ec))
return 0;
} else {
if (wait_event_timeout(ec->wait,
ec_transaction_completed(ec),
- msecs_to_jiffies(1)))
+ usecs_to_jiffies(usecs)))
return 0;
}
spin_lock_irqsave(&ec->lock, flags);
- advance_transaction(ec);
+ if (time_after(jiffies,
+ ec->curr->timestamp +
+ usecs_to_jiffies(usecs)))
+ advance_transaction(ec);
spin_unlock_irqrestore(&ec->lock, flags);
} while (time_before(jiffies, delay));
pr_debug("controller reset, restart transaction\n");
--
1.7.10