linux-kernel - Re: [PATCH] drm/rockchip: Cope with endpoints that haven't been registered yet

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Date:   Sun, 21 Mar 2021 19:58:13 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Sandy Huang <hjc@...k-chips.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jonathan McDowell <noodles@...th.li>
Subject: Re: [PATCH] drm/rockchip: Cope with endpoints that haven't been registered yet

Hi Jonathan,

Am Dienstag, 16. März 2021, 19:27:53 CET schrieb Jonathan McDowell:
> The Rockchip RGB CRTC output driver attempts to avoid probing Rockchip
> subdrivers to see if they're a connected panel or bridge. However part
> of its checks assumes that if no OF platform device is found then it
> can't be a valid bridge or panel. This causes issues with I2C controlled
> bridges that have not yet been registered to the point they can be
> found.
> 
> Change this to return EPROBE_DEFER instead of ENODEV and don't ignore
> such devices. The subsequent call to drm_of_find_panel_or_bridge() will
> return EPROBE_DEFER as well if there's actually a valid device we should
> wait for.
> 
> Signed-off-by: Jonathan McDowell <noodles@...th.li>
> ---
>  drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 8 ++++++--
>  drivers/gpu/drm/rockchip/rockchip_rgb.c     | 7 ++++---
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> index 212bd87c0c4a..b0d63a566501 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> @@ -270,11 +270,15 @@ int rockchip_drm_endpoint_is_subdriver(struct device_node *ep)
>  	if (!node)
>  		return -ENODEV;
>  
> -	/* status disabled will prevent creation of platform-devices */
> +	/*
> +	 * status disabled will prevent creation of platform-devices,
> +	 * but equally we can't rely on the driver having been registered
> +	 * yet (e.g. I2C bridges).
> +	 */
>  	pdev = of_find_device_by_node(node);
>  	of_node_put(node);
>  	if (!pdev)
> -		return -ENODEV;
> +		return -EPROBE_DEFER;

In general, how does that relate to i2c-bridge-drivers, as
of_find_device_by_node supposedly only acts on platform-devices?

Also if that points to a disabled bridge (hdmi, etc) that would likely make
it probe-defer indefinitly, as that device will never become available?

Maybe we could do something like of_device_is_available() which checks
the status property of the node. So something like:

  	pdev = of_find_device_by_node(node);
  	if (!pdev) {
		bool avail = of_device_is_available(node);

		of_node_put(node);

		/* if disabled
		if (!avail)
			return -ENODEV;
		else
			return -EPROBE_DEFER;
	}
  	of_node_put(node);

Though I still do not understand how that should actually pick up on
i2c devices at all.


Heiko