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[media] em28xx: use a better value for I2C timeouts

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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>
This commit is contained in:
Mauro Carvalho Chehab 2013-12-28 07:42:47 -03:00
parent d1b7213b48
commit d20e4ed6d3
1 changed files with 15 additions and 2 deletions
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17
drivers/media/usb/em28xx/em28xx.h
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@ -183,8 +183,21 @@
#define EM28XX_INTERLACED_DEFAULT 1
/* time in msecs to wait for i2c writes 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 EM28XX_I2C_XFER_TIMEOUT 36
/* time in msecs to wait for AC97 xfers to finish */
#define EM28XX_AC97_XFER_TIMEOUT 100