Hi, Bo-Chen: On Tue, 2022-07-12 at 19:12 +0800, Bo-Chen Chen wrote: > From: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx> > > This patch adds a embedded displayport driver for the MediaTek mt8195 > SoC. > > It supports the MT8195, the embedded DisplayPort units. It offers > DisplayPort 1.4 with up to 4 lanes. > > The driver creates a child device for the phy. The child device will > never exist without the parent being active. As they are sharing a > register range, the parent passes a regmap pointer to the child so > that > both can work with the same register range. The phy driver sets > device > data that is read by the parent to get the phy device that can be > used > to control the phy properties. > > This driver is based on an initial version by > Jitao shi <jitao.shi@xxxxxxxxxxxx> > > Signed-off-by: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx> > Signed-off-by: Guillaume Ranquet <granquet@xxxxxxxxxxxx> > Signed-off-by: Bo-Chen Chen <rex-bc.chen@xxxxxxxxxxxx> > --- [snip] > +static void mtk_dp_hpd_sink_event(struct mtk_dp *mtk_dp) > +{ > + ssize_t ret; > + u8 sink_count; > + u8 link_status[DP_LINK_STATUS_SIZE] = {}; > + u32 sink_count_reg = DP_SINK_COUNT_ESI; > + u32 link_status_reg = DP_LANE0_1_STATUS; > + > + ret = drm_dp_dpcd_readb(&mtk_dp->aux, sink_count_reg, > &sink_count); According to your last reply, if drm_dp_dpcd_readb() fail, we could skip below statement. So this just for error checking? If so, the next drm_dp_dpcd_read() would also do the error checking, so the checking here is redundant. Regards, CK > + if (ret < 1) { > + drm_err(mtk_dp->drm_dev, "Read sink count failed\n"); > + return; > + } > + > + drm_dbg(mtk_dp->drm_dev, > + "read sink count from dpcd: %d\n", sink_count); > + > + ret = drm_dp_dpcd_read(&mtk_dp->aux, link_status_reg, > link_status, > + sizeof(link_status)); > + if (!ret) { > + drm_err(mtk_dp->drm_dev, "Read link status failed\n"); > + return; > + } > + > + if (!drm_dp_channel_eq_ok(link_status, mtk_dp- > >train_info.lane_count)) { > + drm_err(mtk_dp->drm_dev, "Channel EQ failed\n"); > + return; > + } > + > + if (link_status[1] & DP_REMOTE_CONTROL_COMMAND_PENDING) > + drm_dp_dpcd_writeb(&mtk_dp->aux, > DP_DEVICE_SERVICE_IRQ_VECTOR, > + DP_REMOTE_CONTROL_COMMAND_PENDING); > +} > +