From: Peter Swain <pswain@xxxxxxxxxx>
Some versions can deliver low-level twsi irq before twsi_ctl.iflg
is set, leading to timeout-driven i/o.
When an irq signals event, but woken task does not see the expected
twsi_ctl.iflg, re-check about 80uS later.
EEPROM reads on 100kHz i2c now measure ~5.2kB/s, about 1/2 what's
achievable, and much better than the worst-case 100 bytes/sec before.
Signed-off-by: Peter Swain <pswain@xxxxxxxxxx>
Signed-off-by: Jan Glauber <jglauber@xxxxxxxxxx>
Acked-by: David Daney <ddaney@xxxxxxxxxxxxxxxxxx>
---
drivers/i2c/busses/i2c-octeon.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)
diff --git a/drivers/i2c/busses/i2c-octeon.c b/drivers/i2c/busses/i2c-octeon.c
index bb15a9c..e3552e5 100644
--- a/drivers/i2c/busses/i2c-octeon.c
+++ b/drivers/i2c/busses/i2c-octeon.c
@@ -130,6 +130,14 @@ static int timeout = 2;
module_param(timeout, int, 0444);
MODULE_PARM_DESC(timeout, "Low-level device timeout (ms)");
+/*
+ * On some hardware IFLG is not visible in TWSI_CTL until after low-level IRQ,
+ * so re-sample CTL a short time later to avoid stalls.
+ */
+static int irq_early_us = 80;
+module_param(irq_early_us, int, 0644);
+MODULE_PARM_DESC(irq_early_us, "Re-poll for IFLG after IRQ (us)");
+
static void writeqflush(u64 val, void __iomem *addr)
{
__raw_writeq(val, addr);
@@ -343,6 +351,26 @@ static int octeon_i2c_test_iflg(struct octeon_i2c *i2c)
return (octeon_i2c_read_ctl(i2c) & TWSI_CTL_IFLG) != 0;
}
+/*
+ * Wait-helper which addresses the delayed-IFLAG problem by re-polling for
+ * missing TWSI_CTL[IFLG] a few us later, when irq has signalled an event,
+ * but none found. Skip this re-poll on the first (non-wakeup) call.
+ */
+static int poll_iflg(struct octeon_i2c *i2c, int *first_p)
+{
+ int iflg = octeon_i2c_test_iflg(i2c);
+
+ if (iflg)
+ return 1;
+ if (*first_p)
+ *first_p = 0;
+ else {
+ usleep_range(irq_early_us, 2 * irq_early_us);
+ iflg = octeon_i2c_test_iflg(i2c);
+ }
+ return iflg;
+}
+
/**
* octeon_i2c_wait - wait for the IFLG to be set
* @i2c: The struct octeon_i2c
@@ -351,10 +379,11 @@ static int octeon_i2c_test_iflg(struct octeon_i2c *i2c)
*/
static int octeon_i2c_wait(struct octeon_i2c *i2c)
{
+ int first = 1;
long result;
i2c->int_en(i2c);
- result = wait_event_timeout(i2c->queue, octeon_i2c_test_iflg(i2c),
+ result = wait_event_timeout(i2c->queue, poll_iflg(i2c, &first),
i2c->adap.timeout);
i2c->int_dis(i2c);
if (!result) {
--
1.9.1
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