[Intel-gfx] [PATCH 3/3] drm/i915: Prevent zero length "index" write

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

The hardware always writes one or two bytes in the index portion of
an indexed transfer. Make sure the message we send as the index
doesn't have a zero length.

Cc: stable at vger.kernel.org
Cc: Daniel Kurtz <djkurtz at chromium.org>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Sean Paul <seanpaul at chromium.org>
Fixes: 56f9eac05489 ("drm/i915/intel_i2c: use INDEX cycles for i2c read transactions")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_i2c.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 4b4528d7010f..8c6b26b5c3fb 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -439,7 +439,8 @@ gmbus_is_index_read(struct i2c_msg *msgs, int i, int num)
 {
 	return (i + 1 < num &&
 		msgs[i].addr == msgs[i + 1].addr &&
-		!(msgs[i].flags & I2C_M_RD) && msgs[i].len <= 2 &&
+		!(msgs[i].flags & I2C_M_RD) &&
+		(msgs[i].len == 1 || msgs[i].len == 2) &&
 		(msgs[i + 1].flags & I2C_M_RD));
 }
 
-- 
2.13.6