linux-kernel - Re: [PATCH] PCI: of: Update parent unit address generation in of_pci_prop_intr

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Message-ID: <af3f61d0-7288-76fa-9d4c-9b33e8411f8a@amd.com>
Date: Mon, 18 Aug 2025 08:11:00 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>, <linux-kernel@...r.kernel.org>
CC: <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH] PCI: of: Update parent unit address generation in
 of_pci_prop_intr_map()


On 8/18/25 02:35, Lorenzo Pieralisi wrote:
> Some interrupt controllers require an #address-cells property in their
> bindings without requiring a "reg" property to be present.
>
> The current logic used to craft an interrupt-map property in
> of_pci_prop_intr_map() is based on reading the #address-cells
> property in the interrupt-parent and, if != 0, read the interrupt
> parent "reg" property to determine the parent unit address to be
> used to create the parent unit interrupt specifier.
>
> First of all, it is not correct to read the "reg" property of
> the interrupt-parent with an #address-cells value taken from the
> interrupt-parent node, because the #address-cells value define the
> number of address cells required by child nodes.
>
> More importantly, for all modern interrupt controllers, the parent
> unit address is irrelevant in HW in relation to the
> device<->interrupt-controller connection and the kernel actually
> ignores the parent unit address value when hierarchically parsing
> the interrupt-map property (ie of_irq_parse_raw()).
>
> For the reasons above, remove the code parsing the interrupt
> parent "reg" property in of_pci_prop_intr_map() - it is not
> needed and as it is it is detrimental in that it prevents
> interrupt-map property generation on systems with an
> interrupt-controller that has no "reg" property in its
> interrupt-controller node - and leave the parent unit address
> always initialized to 0 since it is simply ignored by the kernel.
>
> Signed-off-by: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Lizhi Hou <lizhi.hou@....com>
> Link: https://lore.kernel.org/lkml/aJms+YT8TnpzpCY8@lpieralisi/
> ---
>   drivers/pci/of_property.c | 21 ++++++++++++++-------
>   1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/pci/of_property.c b/drivers/pci/of_property.c
> index 506fcd507113..09b7bc335ec5 100644
> --- a/drivers/pci/of_property.c
> +++ b/drivers/pci/of_property.c
> @@ -279,13 +279,20 @@ static int of_pci_prop_intr_map(struct pci_dev *pdev, struct of_changeset *ocs,
>   			mapp++;
>   			*mapp = out_irq[i].np->phandle;
>   			mapp++;
> -			if (addr_sz[i]) {
> -				ret = of_property_read_u32_array(out_irq[i].np,
> -								 "reg", mapp,
> -								 addr_sz[i]);
> -				if (ret)
> -					goto failed;
> -			}
> +
> +			/*
> +			 * A device address does not affect the
> +			 * device<->interrupt-controller HW connection for all
> +			 * modern interrupt controllers; moreover, the kernel
> +			 * (ie of_irq_parse_raw()) ignores the values in the
> +			 * parent unit address cells while parsing the interrupt-map
> +			 * property because they are irrelevant for interrupts mapping
> +			 * in modern system.
> +			 *
> +			 * Leave the parent unit address initialized to 0 - just
> +			 * take into account the #address-cells size to build
> +			 * the property properly.
> +			 */
Reviewed-by: Lizhi Hou <lizhi.hou@....com>
>   			mapp += addr_sz[i];
>   			memcpy(mapp, out_irq[i].args,
>   			       out_irq[i].args_count * sizeof(u32));