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Subject[PATCH 1/2] drm/i915/intel_i2c: handle zero-length reads
Date
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.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
---
drivers/gpu/drm/i915/intel_i2c.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index cab879f..e249160 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -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;
}
--
1.7.7.3


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