Re: [PATCH v8 06/29] phy: rockchip: usbdp: Drop seamless DP takeover

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Unconditionally disabling the active DP PHY while the upstream display controller is still streaming data causes an AXI bus stall and system hang on Rockchip SoCs.
- [High] Forcing DP HPD to disconnected during probe permanently breaks fixed eDP/DP displays.
--

commit 31addd0a9ff6667916e1a40ca73d061ababa8583
Author: Sebastian Reichel <sebastian.reichel@collabora.com>

phy: rockchip: usbdp: Drop seamless DP takeover

This commit drops support for seamless DP takeover from the bootloader. If a
pre-enabled DP PHY is detected, it logs a warning, forces HPD low, and
unconditionally disables the PHY.

Link: https://lore.kernel.org/linux-phy/20260612164107.C7DB21F000E9@smtp.kernel.org/

> diff --git a/drivers/phy/rockchip/phy-rockchip-usbdp.c b/drivers/phy/rockchip/phy-rockchip-usbdp.c
> index 3fc8222fcaec2..f7ff55f03b7cf 100644
> --- a/drivers/phy/rockchip/phy-rockchip-usbdp.c
> +++ b/drivers/phy/rockchip/phy-rockchip-usbdp.c
> @@ -938,10 +939,12 @@ static int rk_udphy_get_initial_status(struct rk_udphy *udphy)
>  	rk_udphy_reset_deassert_all(udphy);
>  
>  	regmap_read(udphy->pma_regmap, CMN_LANE_MUX_AND_EN_OFFSET, &value);
> -	if (FIELD_GET(CMN_DP_LANE_MUX_ALL, value) && FIELD_GET(CMN_DP_LANE_EN_ALL, value))
> -		udphy->status = UDPHY_MODE_DP;
> -	else
> -		rk_udphy_disable(udphy);
> +	if (FIELD_GET(CMN_DP_LANE_MUX_ALL, value) && FIELD_GET(CMN_DP_LANE_EN_ALL, value)) {
> +		dev_info(udphy->dev, "Started with DP PHY pre-enabled; seamless takeover unsupported\n");
> +		rk_udphy_grfreg_write(udphy->vogrf, &cfg->vogrfcfg[udphy->id].hpd_trigger, false);

[Severity: High]
Will forcing HPD low here permanently break fixed eDP or DP displays?

While this pulls HPD low to signal a disconnect, fixed eDP/DP boards do not
use Type-C muxes and will never trigger a re-assertion via Type-C events.
Since the upstream DP controller driver does not know about the VO GRF
override, the HPD signal remains permanently forced low, and the display
will be seen as disconnected by the kernel.

> +	}
> +
> +	rk_udphy_disable(udphy);

[Severity: High]
Could calling rk_udphy_disable() synchronously right after forcing HPD low
trigger an AXI bus stall?

If the DP PHY was left enabled by the bootloader, the upstream display
controller (VOP) might still be actively issuing AXI/AHB transactions to the
PHY. 

The HPD state change via GRF is asynchronous, but this disables the PHY clocks
immediately on the very next line. Removing the clock from an active AXI slave
often causes the bus to stall indefinitely, resulting in a hard system freeze.

>  
>  	return 0;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260626-rockchip-usbdp-cleanup-v8-0-47f682987895@collabora.com?part=6

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