linux-kernel - Re: [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers

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Date:   Thu, 5 Aug 2021 21:35:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Rob Herring <robh@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>, list@...ndingux.net,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers

On Thu, Aug 05, 2021 at 09:21:09PM +0200, Paul Cercueil wrote:
> When the drivers of remote devices (e.g. HDMI chip) are disabled in the
> config, we want the ingenic-drm driver to be able to probe nonetheless
> with the other devices (e.g. internal LCD panel) that are enabled.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> index d261f7a03b18..5e1fdbb0ba6b 100644
> --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> @@ -1058,6 +1058,18 @@ static int ingenic_drm_bind(struct device *dev, bool has_components)
>  	for (i = 0; ; i++) {
>  		ret = drm_of_find_panel_or_bridge(dev->of_node, 0, i, &panel, &bridge);
>  		if (ret) {
> +			/*
> +			 * Workaround for the case where the drivers for the
> +			 * remote devices are not enabled. When that happens,
> +			 * drm_of_find_panel_or_bridge() returns -EPROBE_DEFER
> +			 * endlessly, which prevents the ingenic-drm driver from
> +			 * working at all.
> +			 */
> +			if (ret == -EPROBE_DEFER) {
> +				ret = driver_deferred_probe_check_state(dev);
> +				if (ret == -ENODEV || ret == -ETIMEDOUT)
> +					continue;
> +			}

So you are mucking around with devices on other busses within this
driver?  What could go wrong?  :(

Please use the existing driver core functionality for this type of
thing, it is not unique, no need for this function to be called.

thanks,

greg k-h