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[v3,22/24] em28xx: use a better value for I2C timeouts

Message ID 1388232976-20061-23-git-send-email-mchehab@redhat.com (mailing list archive)
State New, archived
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Commit Message

Mauro Carvalho Chehab Dec. 28, 2013, 12:16 p.m. UTC 
From: Mauro Carvalho Chehab <m.chehab@samsung.com>

In the lack of a better spec, let's assume the timeout
values compatible with SMBus spec:
	http://smbus.org/specs/smbus110.pdf

at chapter 8 - Electrical Characteristics of SMBus devices

Ok, SMBus is a subset of I2C, and not all devices will be
following it, but the timeout value before this patch was not
even following the spec.

So, while we don't have a better guess for it, use 35 + 1
ms as the timeout.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
---
 drivers/media/usb/em28xx/em28xx.h | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)
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Patch

diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
index db47c2236ca4..9af19332b0f1 100644
--- a/drivers/media/usb/em28xx/em28xx.h
+++ b/drivers/media/usb/em28xx/em28xx.h
@@ -183,8 +183,21 @@ 
 
 #define EM28XX_INTERLACED_DEFAULT 1
 
-/* time in msecs to wait for i2c xfers to finish */
-#define EM2800_I2C_XFER_TIMEOUT		20
+/*
+ * Time in msecs to wait for i2c xfers to finish.
+ * 35ms is the maximum time a SMBUS device could wait when
+ * clock stretching is used. As the transfer itself will take
+ * some time to happen, set it to 35 ms.
+ *
+ * Ok, I2C doesn't specify any limit. So, eventually, we may need
+ * to increase this timeout.
+ *
+ * FIXME: this assumes that an I2C message is not longer than 1ms.
+ * This is actually dependent on the I2C bus speed, although most
+ * devices use a 100kHz clock. So, this assumtion is true most of
+ * the time.
+ */
+#define EM2800_I2C_XFER_TIMEOUT		36
 
 /* time in msecs to wait for AC97 xfers to finish */
 #define EM2800_AC97_XFER_TIMEOUT	100