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drm/i915/intel_i2c: handle zero-length writes

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A common method of probing an i2c bus is trying to do a zero-length write.
Handle this case by checking the length first before decrementing it.

This is actually important, since attempting a zero-length write 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.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Daniel Kurtz 2012-03-30 19:46:36 +08:00 committed by Daniel Vetter
parent 3fdcf43192
commit 26883c31b0
1 changed files with 4 additions and 3 deletions
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7
drivers/gpu/drm/i915/intel_i2c.c
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@ -248,9 +248,10 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
u32 val, loop;
val = loop = 0;
do {
val |= *buf++ << (8 * loop);
} while (--len && ++loop < 4);
while (len && loop < 4) {
val |= *buf++ << (8 * loop++);
len -= 1;
}
I915_WRITE(GMBUS3 + reg_offset, val);
I915_WRITE(GMBUS1 + reg_offset,