linux-kernel - Re: [PATCH v3 08/15] drm/rockchip: analogix_dp: Add support to get panel from the DP AUX bus

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Message-ID: <aiggslcdbdmnc2amlvmzycyxmu3f5zp6kt4ifgzq5gkuugmnem@oqnwf4o7hbss>
Date: Fri, 20 Dec 2024 02:16:41 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Damon Ding <damon.ding@...k-chips.com>
Cc: heiko@...ech.de, robh@...nel.org, krzk+dt@...nel.org, 
	conor+dt@...nel.org, rfoss@...nel.org, vkoul@...nel.org, 
	sebastian.reichel@...labora.com, cristian.ciocaltea@...labora.com, l.stach@...gutronix.de, 
	andy.yan@...k-chips.com, hjc@...k-chips.com, algea.cao@...k-chips.com, 
	kever.yang@...k-chips.com, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-phy@...ts.infradead.org
Subject: Re: [PATCH v3 08/15] drm/rockchip: analogix_dp: Add support to get
 panel from the DP AUX bus

On Thu, Dec 19, 2024 at 04:05:57PM +0800, Damon Ding wrote:
> The rockchip_dp_of_panel_on_aux_bus() helps to check whether the DT
> configurations related to the DP AUX bus are correct or not.
> 
> If failed to get the panel from the platform bus, it is good to try
> the DP AUX bus. Then, the probing process will continue until it enters
> the analogix_dp_bind(), where devm_of_dp_aux_populate_bus() is called
> after &analogix_dp_device.aux has been initialized.

No. devm_of_dp_aux_populate_bus() should be called before bind(). And
bind should only be called from the done_probing() callback. The reason
is very simple: the panel driver might be built as a module and might be
not available when the analogix driver is being probed.

Also, please invert the logic of the commit message (and the driver).
The platform bus should be a fallback if there is no AUX bus panel, not
other way around.

> 
> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
> ---
>  .../gpu/drm/rockchip/analogix_dp-rockchip.c   | 24 +++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> index ba5263f85ee2..60c902abf40b 100644
> --- a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> +++ b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> @@ -317,6 +317,24 @@ static const struct drm_encoder_helper_funcs rockchip_dp_encoder_helper_funcs =
>  	.atomic_check = rockchip_dp_drm_encoder_atomic_check,
>  };
>  
> +static bool rockchip_dp_of_panel_on_aux_bus(const struct device_node *np)
> +{
> +	struct device_node *bus_node, *panel_node;
> +
> +	bus_node = of_get_child_by_name(np, "aux-bus");
> +	if (!bus_node)
> +		return false;
> +
> +	panel_node = of_get_child_by_name(bus_node, "panel");
> +	of_node_put(bus_node);
> +	if (!panel_node)
> +		return false;
> +
> +	of_node_put(panel_node);
> +
> +	return true;
> +}
> +
>  static int rockchip_dp_of_probe(struct rockchip_dp_device *dp)
>  {
>  	struct device *dev = dp->dev;
> @@ -435,8 +453,10 @@ static int rockchip_dp_probe(struct platform_device *pdev)
>  		return -ENODEV;
>  
>  	ret = drm_of_find_panel_or_bridge(dev->of_node, 1, 0, &panel, NULL);
> -	if (ret < 0)
> -		return ret;
> +	if (ret < 0) {
> +		if (!rockchip_dp_of_panel_on_aux_bus(dev->of_node))
> +			return ret;
> +	}
>  
>  	dp = devm_kzalloc(dev, sizeof(*dp), GFP_KERNEL);
>  	if (!dp)
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry