[AMD Official Use Only - Internal Distribution Only] > ________________________________________ > 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. > > > --- > > 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
