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SubjectRe: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort driver
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Hi, Rex:

On Tue, 2022-06-07 at 20:44 +0800, Rex-BC Chen wrote:
> On Tue, 2022-06-07 at 14:44 +0800, CK Hu wrote:
> > Hi, Rex:
> >
> > On Mon, 2022-05-23 at 12:47 +0200, Guillaume Ranquet wrote:
> > > From: Markus Schneider-Pargmann <msp@baylibre.com>
> > >
> > > This patch adds a 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
> > > Jason-JH.Lin <jason-jh.lin@mediatek.com>.
> > >
> > > Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> > > Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> > > ---
> >
> > [snip]
> >
> > > +
> > > +static int mtk_dp_train_handler(struct mtk_dp *mtk_dp)
> > > +{
> > > + bool training_done = false;
> > > + short max_retry = 50;
> > > + int ret = 0;
> > > +
> > > + do {
> > > + switch (mtk_dp->train_state) {
> > > + case MTK_DP_TRAIN_STATE_STARTUP:
> >
> > mtk_dp->train_state is initialized as MTK_DP_TRAIN_STATE_STARTUP
> > even
> > though HPD ISR does not exist. Does this mean HPD ISR is redundant?
> > If
> > HPD ISR is not redundant, create a new state
> > MTK_DP_TRAIN_STATE_NONE
> > for init state.
> >
>
> Hello CK,
>
> I think we don't need MTK_DP_TRAIN_STATE_NONE.
> Because it's "DP_TRAIN_STATE" not "DP_STATE", I think it's ok if we
> start this state machine with "MTK_DP_TRAIN_STATE_STARTUP".

The initial state is MTK_DP_TRAIN_STATE_STARTUP, and HPD thread would
change state from MTK_DP_TRAIN_STATE_STARTUP to
MTK_DP_TRAIN_STATE_STARTUP, this is redundant. So drop the state change
in HPD thread.

>
> > > + mtk_dp_state_handler(mtk_dp);
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_CHECKCAP;
> > > + break;
> > > +
> > > + case MTK_DP_TRAIN_STATE_CHECKCAP:
> > > + if (mtk_dp_parse_capabilities(mtk_dp)) {
> > > + mtk_dp->train_info.check_cap_count = 0;
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_CHECKEDID;
> > > + } else {
> > > + mtk_dp->train_info.check_cap_count++;
> > > +
> > > + if (mtk_dp->train_info.check_cap_count
> > > >
> > >
> > > + MTK_DP_CHECK_SINK_CAP_TIMEOUT_COUNT
> > > ) {
> > > + mtk_dp-
> > > > train_info.check_cap_count = 0;
> > >
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_DPIDLE;
> > > + ret = -ETIMEDOUT;
> > > + }
> > > + }
> > > + break;
> > > +
> > > + case MTK_DP_TRAIN_STATE_CHECKEDID:
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_TRAINING_PRE;
> >
> > MTK_DP_TRAIN_STATE_CHECKEDID is a redundant state, drop it.
> >
> > > + break;
> > > +
> > > + case MTK_DP_TRAIN_STATE_TRAINING_PRE:
> > > + mtk_dp_state_handler(mtk_dp);
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_TRAINING;
> > > + break;
> > > +
> > > + case MTK_DP_TRAIN_STATE_TRAINING:
> > > + ret = mtk_dp_train_start(mtk_dp);
> > > + if (ret == 0) {
> > > + mtk_dp_video_mute(mtk_dp, true);
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_NORMAL;
> > > + mtk_dp_fec_enable(mtk_dp, mtk_dp-
> > > > has_fec);
> > >
> > > + } else if (ret != -EAGAIN) {
> > > + mtk_dp->train_state =
> > > MTK_DP_TRAIN_STATE_DPIDLE;
> > > + }
> > > + break;
> > > + case MTK_DP_TRAIN_STATE_NORMAL:
> > > + mtk_dp_state_handler(mtk_dp);
> > > + training_done = true;
> > > + break;
> > > + case MTK_DP_TRAIN_STATE_DPIDLE:
> >
> > When would this case happen?
> >
> > Regards,
> > CK
>
> Yes, if it's disconnected if we are still training for dp.
> or failed to training min spec RBR.

I mean, every time state change to MTK_DP_TRAIN_STATE_DPIDLE, it would
jump out of this loop and would not get into this loop, so this case
would never get in. This is redundant, so remove this.

Regards,
CK

>
> BRs,
> Rex
> >
> > > + break;
> > > + default:
> > > + break;
> > > + }
> > > +
> > > + if (ret) {
> > > + if (ret == -EAGAIN)
> > > + continue;
> > > + /*
> > > + * If we get any other error number, it doesn't
> > > + * make any sense to keep iterating.
> > > + */
> > > + break;
> > > + }
> > > + } while (!training_done || --max_retry);
> > > +
> > > + return ret;
> > > +}
> >
> >
>
>

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