Re: [PATCH v7 1/2] drm/mediatek: Adjust bandwidth limit for DP

["LIANKUN YANG (杨连坤)" <Liankun.Yang@mediatek.com>]

On Wed, 2025-11-19 at 09:18 +0000, CK Hu (胡俊光) wrote:
> On Tue, 2025-11-04 at 16:55 +0800, Liankun Yang wrote:
> > By adjusting the order of link training and relocating it to HPD,
> > link training can identify the usability of each lane in the
> > current link.
> > 
> > It also supports handling signal instability and weakness due to
> > environmental issues, enabling the acquisition of a stable
> > bandwidth
> > for the current link. Subsequently, DP work can proceed based on
> > the actual maximum bandwidth.
> > 
> > It should training in the hpd event thread.
> > Check the mode with lane count and link rate of training.
> > 
> > If we're eDP and capabilities were already parsed we can skip
> > reading again because eDP panels aren't hotpluggable hence the
> > caps and training information won't ever change in a boot life
> > 
> > Therefore, bridge typec judgment is required for edp training in
> > atomic_enable function.
> > 
> > The `mtk_dp_aux_panel_poweron` function fails to align.
> > Within the `mtk_dp_hpd_event_thread`, if DP is disconnected,
> > the `mtk_dp_aux_panel_poweron` function will write from `aux` to
> > `DPRX`,
> > causing a failure and thus preventing symmetry.
> 
> I'm curious about another case.
> In your description, when DP plug out and plug in, DRM core would not
> call mtk_dp_bridge_atomic_enable(), right?
> If so, when I plug out DP, and plug in another DP panel which support
> smaller resolution,
> then mtk_dp_bridge_atomic_enable() is not called and below call
> sequence would not happen:
> 
> mtk_dp_bridge_atomic_enable() -> mtk_dp_video_enable() ->
> mtk_dp_set_tx_out() -> mtk_dp_setup_tu()
> 
> In mtk_dp_setup_tu, it would set sram_read_start according to
> lane_count.
> But the call sequence would not happen when new plug in, the
> sram_read_start would be old value which may incorrect.
> If think that when plug in and plug out, it should disable DP and
> then enable DP again.
> If DRM core does not do this, I think we should modify DRM core or
> you should reconfig the whole DP when plug in, not only training.
> 
> Regards,
> CK
> 

Hi CK

When DP plug out, DRM core will call mtk_dp_bridge_atomic_disable().
When DP plug in, DRM core will call mtk_dp_bridge_atomic_enable().

If DP plug in, sram_read_start will be recalculate based on the lane
count.

Regards
Liankun.

> 
> > 
> > Signed-off-by: Liankun Yang <liankun.yang@mediatek.com>
> > ---
> > Change in V7:
> > - Separate the edp part:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250822120506.15486-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9dixTD-P0$
> >  
> > 
> > Change in V6:
> > - Fixed power on in atomic enable.
> > Per suggestion from the previous thread:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250630080824.7107-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9d2uyXyOA$
> >  
> > 
> > Change in V5:
> > - Fixed the issue that the 4th version of the patch caused DP to
> > have no screen.
> > Per suggestion from the previous thread:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250625095446.31726-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9dptlx1kc$
> >  
> > 
> > Change in V4:
> > - Tested the internal eDP display on MT8195 Tomato and it is fine.
> > Per suggestion from the previous thread:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250318140236.13650-2-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9dTyrYJLQ$
> >  
> > 
> > Change in V3:
> > - Remove 'mtk_dp->enabled = false" in atomic disable.
> > - Remove 'mtk_dp->enabled = true" in atomic enable.
> > Per suggestion from the previous thread:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20241025083036.8829-4-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9drgc9X0o$
> >  
> > 
> > Change in V2:
> > - Adjust DP training timing.
> > - Adjust parse capabilities timing.
> > - Add power on/off for connect/disconnect.
> > Per suggestion from the previous thread:
> > 
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20240315015233.2023-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!k4Lf9UagGvqF5rzqpPtWReo4zF4UzBkmgcHZq0z6q3f7kyA-rtj8kV8uiKP2nryG0sTpORl1Y58Sum9dYxjNtE8$
> >  
> > ---
> >  drivers/gpu/drm/mediatek/mtk_dp.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c
> > b/drivers/gpu/drm/mediatek/mtk_dp.c
> > index bef6eeb30d3e..0ba2c208811c 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> > @@ -1976,6 +1976,7 @@ static irqreturn_t
> > mtk_dp_hpd_event_thread(int hpd, void *dev)
> >  	struct mtk_dp *mtk_dp = dev;
> >  	unsigned long flags;
> >  	u32 status;
> > +	int ret;
> >  
> >  	if (mtk_dp->need_debounce && mtk_dp-
> > >train_info.cable_plugged_in)
> >  		msleep(100);
> > @@ -1994,9 +1995,28 @@ static irqreturn_t
> > mtk_dp_hpd_event_thread(int hpd, void *dev)
> >  			memset(&mtk_dp->info.audio_cur_cfg, 0,
> >  			       sizeof(mtk_dp->info.audio_cur_cfg));
> >  
> > +			mtk_dp->enabled = false;
> > +			/* power off aux */
> > +			mtk_dp_update_bits(mtk_dp,
> > MTK_DP_TOP_PWR_STATE,
> > +					   DP_PWR_STATE_BANDGAP_TPLL,
> > +					   DP_PWR_STATE_MASK);
> > +
> >  			mtk_dp->need_debounce = false;
> >  			mod_timer(&mtk_dp->debounce_timer,
> >  				  jiffies + msecs_to_jiffies(100) - 1);
> > +		} else {
> > +			mtk_dp_aux_panel_poweron(mtk_dp, true);
> > +
> > +			ret = mtk_dp_parse_capabilities(mtk_dp);
> > +			if (ret)
> > +				drm_err(mtk_dp->drm_dev, "Can't parse
> > capabilities\n");
> > +
> > +			/* Training */
> > +			ret = mtk_dp_training(mtk_dp);
> > +			if (ret)
> > +				drm_err(mtk_dp->drm_dev, "Training
> > failed, %d\n", ret);
> > +
> > +			mtk_dp->enabled = true;
> >  		}
> >  	}
> >  
> 
>