Re: [PATCH] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ

On Mon, 30 Dec 2019, Wayne Lin Wayne.Lin@amd.com wrote:

[Why] According to DP spec, it should shift left 4 digits for NO_STOP_BIT in REMOTE_I2C_READ message. Not 5 digits.

[How] Correct the shifting value of NO_STOP_BIT for DP_REMOTE_I2C_READ case in drm_dp_encode_sideband_req().

Which commit introduced the issue? Fixes: tag. Does it need a stable backport? Does this fix a user visible bug?

BR, Jani.

Signed-off-by: Wayne Lin Wayne.Lin@amd.com

drivers/gpu/drm/drm_dp_mst_topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 1d1bfa49ca2b..0557e225ff67 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -393,7 +393,7 @@ drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req, memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes); idx += req->u.i2c_read.transactions[i].num_bytes;

• 	buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 5;
  

• 	buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
  buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
  idx++;
  

  }