On 2020-01-03 12:50 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. > > 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. >
Thanks for elaborating on the potential consequences of this bug. Harry > [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: ad7f8a1f9ce (drm/helper: add Displayport multi-stream helper (v0.6)) > Reviewed-by: Harry Wentland <harry.wentl...@amd.com> > Signed-off-by: Wayne Lin <wayne....@amd.com> > Cc: sta...@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++; > } > _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/amd-gfx
