[PATCH 3.16 019/254] drm/i915: Prevent zero length "index" write

Ben Hutchings
2018-02-28T16:20:42Z

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

commit 56350fb8978bbf4aafe08f21234e161dd128b417 upstream.

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: Daniel Kurtz <djkurtz@chromium.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <seanpaul@chromium.org>
Fixes: 56f9eac05489 ("drm/i915/intel_i2c: use INDEX cycles for i2c read transactions")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171123194157.25367-3-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
(cherry picked from commit bb9e0d4bca50f429152e74a459160b41f3d60fb2)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/gpu/drm/i915/intel_i2c.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -449,7 +449,8 @@ gmbus_is_index_read(struct i2c_msg *msgs
{
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));
}