drm/i915/intel_i2c: handle zero-length reads (79985eee) · Commits · e / devices / android_kernel_oneplus_sm7250

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>

drivers/gpu/drm/i915/intel_i2c.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -217,7 +217,7 @@ gmbus_xfer_read(struct drm_i915_private dev_priv, struct i2c_msg msg,
	(len << GMBUS_BYTE_COUNT_SHIFT) \|		(len << GMBUS_BYTE_COUNT_SHIFT) \|
	(msg->addr << GMBUS_SLAVE_ADDR_SHIFT) \|		(msg->addr << GMBUS_SLAVE_ADDR_SHIFT) \|
	GMBUS_SLAVE_READ \| GMBUS_SW_RDY);		GMBUS_SLAVE_READ \| GMBUS_SW_RDY);
	do {		while (len) {
	int ret;		int ret;
	u32 val, loop = 0;		u32 val, loop = 0;
	u32 gmbus2;		u32 gmbus2;
	@@ -235,7 +235,7 @@ gmbus_xfer_read(struct drm_i915_private dev_priv, struct i2c_msg msg,
	*buf++ = val & 0xff;		*buf++ = val & 0xff;
	val >>= 8;		val >>= 8;
	} while (--len && ++loop < 4);		} while (--len && ++loop < 4);
	} while (len);		}

	return 0;		return 0;
	}		}