| From 5d2818e2f90b4ecf0bacaa90458fd2ec26f5915e Mon Sep 17 00:00:00 2001 |
| From: Wayne Lin <Wayne.Lin@amd.com> |
| Date: Fri, 3 Jan 2020 13:50:01 +0800 |
| Subject: [PATCH] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ |
| |
| commit c4e4fccc5d52d881afaac11d3353265ef4eccb8b upstream. |
| |
| [Why] |
| According to DP spec, it should shift left 4 digits for NO_STOP_BIT |
| in REMOTE_I2C_READ message. Not 5 digits. |
| |
| In current code, NO_STOP_BIT is always set to zero which means I2C |
| master is always generating a I2C stop at the end of each I2C write |
| transaction while handling REMOTE_I2C_READ sideband message. This issue |
| might have the generated I2C signal not meeting the requirement. Take |
| random read in I2C for instance, I2C master should generate a repeat |
| start to start to read data after writing the read address. This issue |
| will cause the I2C master to generate a stop-start rather than a |
| re-start which is not expected in I2C random read. |
| |
| [How] |
| Correct the shifting value of NO_STOP_BIT for DP_REMOTE_I2C_READ case in |
| drm_dp_encode_sideband_req(). |
| |
| Changes since v1:(https://patchwork.kernel.org/patch/11312667/) |
| * Add more descriptions in commit and cc to stable |
| |
| Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)") |
| Reviewed-by: Harry Wentland <harry.wentland@amd.com> |
| Signed-off-by: Wayne Lin <Wayne.Lin@amd.com> |
| Cc: stable@vger.kernel.org |
| Signed-off-by: Lyude Paul <lyude@redhat.com> |
| Link: https://patchwork.freedesktop.org/patch/msgid/20200103055001.10287-1-Wayne.Lin@amd.com |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c |
| index fbfb685e4d2b..688242bc69bb 100644 |
| --- a/drivers/gpu/drm/drm_dp_mst_topology.c |
| +++ b/drivers/gpu/drm/drm_dp_mst_topology.c |
| @@ -333,7 +333,7 @@ static void drm_dp_encode_sideband_req(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++; |
| } |
| -- |
| 2.7.4 |
| |
