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drm/i915/intel_i2c: handle zero-length reads 

A common method of probing an i2c bus is trying to do a zero-length read.
Handle this case by checking the length first waiting for data to be read.

This is actually important, since attempting a zero-length read is one
of the ways that i2cdetect and i2c_new_probed_device detect whether
there is device present on the bus with a given address.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=48269
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Daniel Kurtz 2012-04-13 19:47:53 +08:00 committed by Daniel Vetter
parent f637fde434
commit 79985eee84
1 changed files with 2 additions and 2 deletions
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4
drivers/gpu/drm/i915/intel_i2c.c
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@ -217,7 +217,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
(len << GMBUS_BYTE_COUNT_SHIFT) |
(msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
GMBUS_SLAVE_READ | GMBUS_SW_RDY);
do {
while (len) {
int ret;
u32 val, loop = 0;
u32 gmbus2;
@ -235,7 +235,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
*buf++ = val & 0xff;
val >>= 8;
} while (--len && ++loop < 4);
} while (len);
}
return 0;
}