linux-kernel - Re: [PATCH v1 2/2] drm/tegra: Use drm_dp_aux_register

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Date:   Mon, 8 Nov 2021 16:17:33 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Lyude Paul <lyude@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Graichen <thomas.graichen@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] drm/tegra: Use drm_dp_aux_register_ddc/chardev()
 helpers

On Mon, Nov 08, 2021 at 02:08:21AM +0300, Dmitry Osipenko wrote:
> Use drm_dp_aux_register_ddc/chardev() helpers that allow to register I2C
> adapter separately from the character device. This fixes broken display
> panel driver of Acer Chromebook CB5-311 that fails to probe starting with
> v5.13 kernel when DP AUX registration order was changed. Tegra SOR driver
> is never probed now using the new registration order because tegra-output
> always fails with -EPROBE_DEFER due to missing display panel that requires
> DP AUX DDC to be registered first. The offending commit made DDC to be
> registered after SOR's output, which can't ever happen. Use new helpers
> to restore the registration order and revive display panel.

This feels a bit backward, I think the clean solution would be to untangle
the SOR loading from the panel driver loading, and then only block
registering the overall drm_device on both drivers having loaded.

This here at least feels like a game of whack-a-mole, if like every driver
needs its own careful staging of everything.
-Daniel

> 
> Cc: <stable@...r.kernel.org> # 5.13+
> Fixes: 39c17ae60ea9 ("drm/tegra: Don't register DP AUX channels before connectors")
> Reported-by: Thomas Graichen <thomas.graichen@...il.com> # T124 Nyan Big
> Tested-by: Thomas Graichen <thomas.graichen@...il.com> # T124 Nyan Big
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/gpu/drm/tegra/dpaux.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
> index 1f96e416fa08..e0d675c7c2e5 100644
> --- a/drivers/gpu/drm/tegra/dpaux.c
> +++ b/drivers/gpu/drm/tegra/dpaux.c
> @@ -532,7 +532,9 @@ static int tegra_dpaux_probe(struct platform_device *pdev)
>  	dpaux->aux.transfer = tegra_dpaux_transfer;
>  	dpaux->aux.dev = &pdev->dev;
>  
> -	drm_dp_aux_init(&dpaux->aux);
> +	err = drm_dp_aux_register_ddc(&dpaux->aux);
> +	if (err < 0)
> +		return err;
>  
>  	/*
>  	 * Assume that by default the DPAUX/I2C pads will be used for HDMI,
> @@ -585,6 +587,8 @@ static int tegra_dpaux_remove(struct platform_device *pdev)
>  	pm_runtime_put_sync(&pdev->dev);
>  	pm_runtime_disable(&pdev->dev);
>  
> +	drm_dp_aux_unregister_ddc(&dpaux->aux);
> +
>  	mutex_lock(&dpaux_lock);
>  	list_del(&dpaux->list);
>  	mutex_unlock(&dpaux_lock);
> @@ -718,7 +722,7 @@ int drm_dp_aux_attach(struct drm_dp_aux *aux, struct tegra_output *output)
>  	int err;
>  
>  	aux->drm_dev = output->connector.dev;
> -	err = drm_dp_aux_register(aux);
> +	err = drm_dp_aux_register_chardev(aux);
>  	if (err < 0)
>  		return err;
>  
> @@ -759,7 +763,7 @@ int drm_dp_aux_detach(struct drm_dp_aux *aux)
>  	unsigned long timeout;
>  	int err;
>  
> -	drm_dp_aux_unregister(aux);
> +	drm_dp_aux_unregister_chardev(aux);
>  	disable_irq(dpaux->irq);
>  
>  	if (dpaux->output->panel) {
> -- 
> 2.33.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch