linux-kernel - fw_devlink=on and sunxi HDMI

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Date:   Sun, 16 May 2021 19:05:39 +0200
From:   Ondřej Jirman <megi@....cz>
To:     saravanak@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, mripard@...nel.org, wens@...e.org,
        jernej.skrabec@...il.com, gregkh@...uxfoundation.org,
        rafael@...nel.org, linux-kernel@...r.kernel.org,
        andre.przywara@....com
Subject: fw_devlink=on and sunxi HDMI

Hello,

Linux 5.13-rc1 again has fw_devlink=on enabled by default. I've found that this
breaks probing display pipeline and HDMI output on sunxi boards, because of
fwnode_link between hdmi and hdmi-phy nodes.

HDMI device probe keeps being avoided with these repeated messages in dmesg:

  platform 1ee0000.hdmi: probe deferral - supplier 1ef0000.hdmi-phy not ready

Both nodes have their own compatible, but are implemented by a single
struct device.

This looks like a kind of situation that's expected to break fw_devlink
expectations by my reading of the the e-mails about trying the fw_devlink=on
during 5.12 cycle.

Is this supposed to be solved by implementing the PHY node as it's own
device or by breaking the fwnode_link between the hdmi phy and hdmi nodes?
Seems like second solution would be quicker now that rc1 is out.

Where would be a good place to break that fwnode_link in code?

Or can the fw_devlink code be made aware of this situation, where two fwnodes
are implemented by the same Linux device, somehow?

Relevant references:

https://elixir.bootlin.com/linux/v5.13-rc1/source/drivers/gpu/drm/sun4i/sun8i_hdmi_phy.c#L600
https://elixir.bootlin.com/linux/v5.13-rc1/source/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c#L212
https://elixir.bootlin.com/linux/v5.13-rc1/source/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi#L1176

kind regards,
	o.