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-----Original Message----- From: Lyude Paul lyude@redhat.com Sent: Saturday, January 4, 2020 6:02 AM To: Lin, Wayne Wayne.Lin@amd.com; dri-devel@lists.freedesktop.org; amd-gfx@lists.freedesktop.org Cc: Kazlauskas, Nicholas Nicholas.Kazlauskas@amd.com; Wentland, Harry Harry.Wentland@amd.com; Zuo, Jerry Jerry.Zuo@amd.com; stable@vger.kernel.org Subject: Re: [PATCH v2] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ
Oh! Just a friendly tip, I fixed this before pushing your patch:
➜ drm-maint git:(drm-misc-fixes) dim push dim: 0b1d54cedbb4 ("drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ"): Fixes: SHA1 needs at least 12 digits: dim: ad7f8a1f9ce (drm/helper: add Displayport multi-stream helper (v0.6)) dim: ERROR: issues in commits detected, aborting
For the future, we have a set of DRM maintainer tools (they're quite useful for people who aren't maintainers though!) that you can use to make sure your patch is formatted correctly ahead of time:
https://drm.pages.freedesktop.org/maintainer-tools/dim.html%3E
Particularly useful commands:
- dim sparse # Checks for trivial code issues, like set but unused variables
- dim checkpatch # Checks for code style issues
- dim fixes $COMMIT_ID # Adds an appropriately formatted Fixes: tag
- dim cite $COMMIT_ID # Adds an appropriately formatted Reference: tag
Really appreciate for your time! I will have a look on this. Thanks a lot.
On Fri, 2020-01-03 at 13:50 +0800, Wayne Lin wrote:
[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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2F
patchwork.kernel.org%2Fpatch%2F11312667%2F&data=02%7C01%7Cw ayne.li
n%40amd.com%7Ce4299c1721bd4bcb486708d790989148%7C3dd8961fe4884e 608e11a
82d994e183d%7C0%7C0%7C637136857271065549&sdata=eoxiRojffBepY YoQbjp
j8b6R%2BkwaOQWBoU%2Fu8lY5gIQ%3D&reserved=0)
- Add more descriptions in commit and cc to stable
Fixes: ad7f8a1f9ce (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
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 1cf5f8b8bbb8..9d24c98bece1 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++; }-- Cheers, Lyude Paul
-- Best Regards, Wayne Lin