Re: [PATCH v3 07/10] drm/bridge: synopsys: dw-dp: Add Runtime PM support

From: Sebastian Reichel

Date: Wed Jul 15 2026 - 14:32:38 EST

Hello Andy,

On Tue, Jul 14, 2026 at 05:01:14PM +0800, Andy Yan wrote:
> Hello Sebastian,
>
> Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx> 于2026年6月13日周六 02:01写道：
>
> > Add runtime PM stubs to the Synopsys DesignWare DisplayPort bridge
> > driver. Support is not enabled automatically and must be hooked up
> > in the vendor specific glue code.
> >
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/bridge/synopsys/dw-dp.c | 27 +++++++++++++++++++++++++++
> > include/drm/bridge/dw_dp.h | 3 +++
> > 2 files changed, 30 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> > b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> > index 7fa38145e35c..7f4f36c61484 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> > @@ -1465,6 +1465,8 @@ static ssize_t dw_dp_aux_transfer(struct drm_dp_aux
> > *aux,
> > if (WARN_ON(msg->size > 16))
> > return -E2BIG;
> >
> > + ACQUIRE(pm_runtime_active_auto, pm)(dp->dev);
> > +
> > switch (msg->request & ~DP_AUX_I2C_MOT) {
> > case DP_AUX_NATIVE_WRITE:
> > case DP_AUX_I2C_WRITE:
> > @@ -1655,6 +1657,8 @@ static void dw_dp_bridge_atomic_enable(struct
> > drm_bridge *bridge,
> > struct drm_connector_state *conn_state;
> > int ret;
> >
> > + pm_runtime_get_sync(dp->dev);
> > +
> > connector = drm_atomic_get_new_connector_for_encoder(state,
> > bridge->encoder);
> > if (!connector) {
> > dev_err(dp->dev, "failed to get connector\n");
> > @@ -1709,6 +1713,7 @@ static void dw_dp_bridge_atomic_disable(struct
> > drm_bridge *bridge,
> > dw_dp_link_disable(dp);
> > bitmap_zero(dp->sdp_reg_bank, SDP_REG_BANK_SIZE);
> > dw_dp_reset(dp);
> > + pm_runtime_put_autosuspend(dp->dev);
> > }
> >
> > static bool dw_dp_hpd_detect_link(struct dw_dp *dp, struct drm_connector
> > *connector)
> > @@ -1729,6 +1734,8 @@ static enum drm_connector_status
> > dw_dp_bridge_detect(struct drm_bridge *bridge,
> > {
> > struct dw_dp *dp = bridge_to_dp(bridge);
> >
> > + ACQUIRE(pm_runtime_active_auto, pm)(dp->dev);
> >
>
> This may not work correctly. Per the DW-DP TRM, the " HPD_HOT_PLUG
> bit is asserted only after the sink is attached and holds HPD high
> for at least 100ms". Consequently, reading this bit within 100ms
> after resuming runtime_pm may fail to detect the status. I've
> verified this behavior on a Rock 5B board—the HPD bit remains
> unreadable at this point.
>
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> @@ -1761,12 +1761,17 @@ static enum drm_connector_status
> dw_dp_bridge_detect(struct drm_bridge *bridge,
>
> ACQUIRE(pm_runtime_active_auto, pm)(dp->dev);
>
> - if (!dw_dp_hpd_detect(dp))
> + if (!dw_dp_hpd_detect(dp)) {
> + printk(KERN_DEBUG "%s no hpd\n", __func__);
> return connector_status_disconnected;
> + }
>
> - if (!dw_dp_hpd_detect_link(dp, connector))
> + if (!dw_dp_hpd_detect_link(dp, connector)) {
> + printk(KERN_DEBUG "%s no link\n", __func__);
> return connector_status_disconnected;
> + }
>
> + printk(KERN_DEBUG "%s connected\n", __func__);
> return connector_status_connected;
> }
>
> @@ -2149,6 +2154,7 @@ static irqreturn_t dw_dp_irq(int irq, void *data)
> u32 value;
>
> regmap_read(dp->regmap, DW_DP_GENERAL_INTERRUPT, &value);
> + printk(KERN_DEBUG "%s value: %d\n", __func__, value);
> if (!value)
> return IRQ_NONE;
>
> bootup
> [ 5.218035] panthor fb000000.gpu: [drm] Using Transparent Hugepage
> [ 5.219073] [drm] Initialized panthor 1.9.0 for fb000000.gpu on minor 1
> [ 7.953973] r8169 0004:41:00.0 enP4p65s0: Link is Up - 1Gbps/Full - flow
> control off
> [ 8.601273] dw_dp_rockchip_runtime_resume ret: 0
> [ 8.702748] dw_dp_irq value: 1 // (HPD irq 100 100ms after
> runtime_resume)
> [ 8.714236] dw_dp_irq value: 2
> [ 8.714775] dw_dp_irq value: 2
> [ 8.715201] dw_dp_irq value: 2
> [ 8.715710] dw_dp_irq value: 2
> [ 8.715744] dw_dp_bridge_detect connected
> [ 9.226752] dw_dp_rockchip_runtime_suspend
>
>
> Then run modetest:
>
> # modetest
> trying to open device '/dev/dri/card1'... is not a KMS device
> trying to open device '/dev/dri/card0'... done
> opened device `RockChip Soc DRM` on driver `rockchip` (version 1.0.0 at 0)
> Encoders:
> id crtc type possible crtcs possible clones
> 86 0 TMDS 0x00000004 0x00000001
> 88 0 TMDS 0x00000001 0x00000002
> 92 0 TMDS 0x00000002 0x00000004
>
> Connectors:
> id encoder status name size (mm) modes
> encoders
> 87 0 disconnected DP-1 0x0 0 86
> props:
> 1 EDID:
>
> [ 13.809398] rockchip-pm-domain
> fd8d8000.power-management:power-controller: sync_state() pending due to
> fdee0000.hdmi_receiver
> [ 29.225506] dw_dp_rockchip_runtime_resume ret: 0
> [ 29.225940] dw_dp_bridge_detect no hpd // no HPD read here
> [ 29.326986] dw_dp_irq value: 1 // HPD irq ater
> 100ms
> [ 29.346609] dw_dp_irq value: 2
> [ 29.347150] dw_dp_irq value: 2
> [ 29.347578] dw_dp_irq value: 2
> [ 29.348092] dw_dp_irq value: 2
>
>
> if I add a mdelay(110) after ACQUIRE pm_runtime, the hdp can be read.
> index 02ca7fe725876..5959e79eb3e2b 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> @@ -1760,7 +1760,7 @@ static enum drm_connector_status
> dw_dp_bridge_detect(struct drm_bridge *bridge,
> struct dw_dp *dp = bridge_to_dp(bridge);
>
> ACQUIRE(pm_runtime_active_auto, pm)(dp->dev);
> -
> + mdelay(110);

Interesting, I did not notice this issue with the Sige 5 (RK3576).
Thanks for not just reporting it to not work, but also figuring out
what is going on :) I will add an msleep(110); in the next version.

Greetings,

-- Sebastian

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