linux-kernel - Re: [PATCH] of/irq: Add msi-parent check to of_msi

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Message-ID: <20250918135555.GA1540012-robh@kernel.org>
Date: Thu, 18 Sep 2025 08:55:55 -0500
From: Rob Herring <robh@...nel.org>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org,
	Sascha Bischoff <sascha.bischoff@....com>,
	Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH] of/irq: Add msi-parent check to of_msi_xlate()

On Tue, Sep 16, 2025 at 11:18:58AM +0200, Lorenzo Pieralisi wrote:
> In some legacy platforms the MSI controller for a PCI host
> bridge is identified by an msi-parent property whose phandle
> points at an MSI controller node with no #msi-cells property,
> that implicitly means #msi-cells == 0.
> 
> For such platforms, mapping a device ID and retrieving the
> MSI controller node becomes simply a matter of checking
> whether in the device hierarchy there is an msi-parent property
> pointing at an MSI controller node with such characteristics.
> 
> Add a helper function to of_msi_xlate() to check the msi-parent
> property in addition to msi-map and retrieve the MSI controller
> node (with a 1:1 ID deviceID-IN<->deviceID-OUT mapping) to
> provide support for deviceID mapping and MSI controller node
> retrieval for such platforms.

Your line wrapping is a bit short.

I had a look at who is parsing "msi-parent" themselves as that's 
typically a recipe for doing it incorrectly ('interrupt-map' anyone). 
Can we make iproc_pcie_msi_enable() use this? It's quite ugly reaching 
into the GICv3 node...

And perhaps irq-gic-its-msi-parent.c could use this? 

And looks like pcie-layerscape-gen4 is leaking a node reference...

> 
> Signed-off-by: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Cc: Sascha Bischoff <sascha.bischoff@....com>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> ---
>  drivers/of/irq.c | 38 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 35 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/of/irq.c b/drivers/of/irq.c
> index e7c12abd10ab..d0e2dfd0ee28 100644
> --- a/drivers/of/irq.c
> +++ b/drivers/of/irq.c
> @@ -670,6 +670,35 @@ void __init of_irq_init(const struct of_device_id *matches)
>  	}
>  }
>  
> +static int of_check_msi_parent(struct device_node *dev_node, struct device_node **msi_node)
> +{
> +	struct of_phandle_args msi_spec;
> +	int ret;
> +
> +	/*
> +	 * An msi-parent phandle with a missing or == 0 #msi-cells
> +	 * property identifies a 1:1 ID translation mapping.
> +	 *
> +	 * Set the msi controller node if the firmware matches this
> +	 * condition.
> +	 */
> +	ret = of_parse_phandle_with_optional_args(dev_node, "msi-parent", "#msi-cells",
> +						  0, &msi_spec);
> +	if (!ret) {
> +		if ((*msi_node && *msi_node != msi_spec.np) || msi_spec.args_count != 0)
> +			ret = -EINVAL;
> +
> +		if (!ret) {
> +			/* Return with a node reference held */
> +			*msi_node = msi_spec.np;
> +			return 0;
> +		}
> +		of_node_put(msi_spec.np);
> +	}
> +
> +	return ret;
> +}
> +
>  /**
>   * of_msi_xlate - map a MSI ID and find relevant MSI controller node
>   * @dev: device for which the mapping is to be done.
> @@ -677,7 +706,7 @@ void __init of_irq_init(const struct of_device_id *matches)
>   * @id_in: Device ID.
>   *
>   * Walk up the device hierarchy looking for devices with a "msi-map"
> - * property. If found, apply the mapping to @id_in.
> + * or "msi-parent" property. If found, apply the mapping to @id_in.
>   * If @msi_np points to a non-NULL device node pointer, only entries targeting
>   * that node will be matched; if it points to a NULL value, it will receive the
>   * device node of the first matching target phandle, with a reference held.
> @@ -691,12 +720,15 @@ u32 of_msi_xlate(struct device *dev, struct device_node **msi_np, u32 id_in)
>  
>  	/*
>  	 * Walk up the device parent links looking for one with a
> -	 * "msi-map" property.
> +	 * "msi-map" or an "msi-parent" property.
>  	 */
> -	for (parent_dev = dev; parent_dev; parent_dev = parent_dev->parent)
> +	for (parent_dev = dev; parent_dev; parent_dev = parent_dev->parent) {
>  		if (!of_map_id(parent_dev->of_node, id_in, "msi-map",
>  				"msi-map-mask", msi_np, &id_out))
>  			break;
> +		if (!of_check_msi_parent(parent_dev->of_node, msi_np))
> +			break;
> +	}
>  	return id_out;
>  }
>  
> -- 
> 2.48.0
>