On 2019-12-30 11:00 p.m., Lin, Wayne wrote: > [AMD Official Use Only - Internal Distribution Only] > Make sure to select the correct AIP designation for public emails. See my email on that from yesterday. :) >> ________________________________________ >> From: Wentland, Harry <Harry.Wentland@xxxxxxx> >> Sent: Monday, December 30, 2019 23:26 >> To: Lin, Wayne; dri-devel@xxxxxxxxxxxxxxxxxxxxx; amd-gfx@xxxxxxxxxxxxxxxxxxxxx >> Cc: lyude@xxxxxxxxxx; Zuo, Jerry; Kazlauskas, Nicholas; Wentland, Harry >> Subject: Re: [PATCH] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ >> >> On 2019-12-30 2:05 a.m., 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. >>> >>> [How] >>> Correct the shifting value of NO_STOP_BIT for DP_REMOTE_I2C_READ case in >>> drm_dp_encode_sideband_req(). >>> >>> Signed-off-by: Wayne Lin <Wayne.Lin@xxxxxxx> >> >> Good catch. Looks like this has been there since the beginning of MST in >> the kernel. How did you find this? Did this cause bad EDID reads or some >> other problem? If so the commit message should probably mention it. >> >> Harry > Thanks for your time. > > I found this while I was trying to debug MST issues by using AUX monitor. > So far, I don't observe problems that relate to this under my test cases and environment. > However, this bit might affect the I2C signal generated by I2C master, I will mention more > in the commit message. > Thanks. Was just curious if you saw any real issues. Good find nevertheless and good patch. You can add my Reviewed-by: Harry Wentland <harry.wentland@xxxxxxx> Harry > Thanks. >> >>> --- >>> 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++; >>> } >>> > -- > Wayne Lin > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
