linux-kernel - Re: [PATCH v2 pci] PCI/MSI: pci-xgene-msi: Enable MSI support in ACPI boot for X-Gene v1

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Date:   Fri, 28 Apr 2017 10:27:34 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Khuong Dinh <kdinh@....com>, lorenzo.pieralisi@....com,
        msalter@...hat.com, bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        jcm@...hat.com
Cc:     patches@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, rjw@...ysocki.net,
        Duc Dang <dhdang@....com>
Subject: Re: [PATCH v2 pci] PCI/MSI: pci-xgene-msi: Enable MSI support in ACPI
 boot for X-Gene v1

On 28/04/17 01:54, Khuong Dinh wrote:
> From: Khuong Dinh <kdinh@....com>
> 
> This patch makes pci-xgene-msi driver ACPI-aware and provides
> MSI capability for X-Gene v1 PCIe controllers in ACPI boot mode.
> 
> Signed-off-by: Khuong Dinh <kdinh@....com>
> Signed-off-by: Duc Dang <dhdang@....com>
> Acked-by: Marc Zyngier <marc.zyngier@....com>
> ---
> v2:
>  - Verify with BIOS version 3.06.25 and 3.07.09
> v1:
>  - Initial version
> ---
>  drivers/pci/host/pci-xgene-msi.c |   35 ++++++++++++++++++++++++++++++++---
>  1 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/host/pci-xgene-msi.c b/drivers/pci/host/pci-xgene-msi.c
> index f1b633b..00aaa3d 100644
> --- a/drivers/pci/host/pci-xgene-msi.c
> +++ b/drivers/pci/host/pci-xgene-msi.c
> @@ -24,6 +24,7 @@
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
>  #include <linux/of_pci.h>
> +#include <linux/acpi.h>
>  
>  #define MSI_IR0			0x000000
>  #define MSI_INT0		0x800000
> @@ -39,7 +40,7 @@ struct xgene_msi_group {
>  };
>  
>  struct xgene_msi {
> -	struct device_node	*node;
> +	struct fwnode_handle	*fwnode;
>  	struct irq_domain	*inner_domain;
>  	struct irq_domain	*msi_domain;
>  	u64			msi_addr;
> @@ -249,6 +250,13 @@ static void xgene_irq_domain_free(struct irq_domain *domain,
>  	.free   = xgene_irq_domain_free,
>  };
>  
> +#ifdef CONFIG_ACPI
> +static struct fwnode_handle *xgene_msi_get_fwnode(struct device *dev)
> +{
> +	return xgene_msi_ctrl.fwnode;
> +}
> +#endif
> +
>  static int xgene_allocate_domains(struct xgene_msi *msi)
>  {
>  	msi->inner_domain = irq_domain_add_linear(NULL, NR_MSI_VEC,
> @@ -256,7 +264,7 @@ static int xgene_allocate_domains(struct xgene_msi *msi)
>  	if (!msi->inner_domain)
>  		return -ENOMEM;
>  
> -	msi->msi_domain = pci_msi_create_irq_domain(of_node_to_fwnode(msi->node),
> +	msi->msi_domain = pci_msi_create_irq_domain(msi->fwnode,
>  						    &xgene_msi_domain_info,
>  						    msi->inner_domain);
>  
> @@ -265,6 +273,9 @@ static int xgene_allocate_domains(struct xgene_msi *msi)
>  		return -ENOMEM;
>  	}
>  
> +#ifdef CONFIG_ACPI
> +	pci_msi_register_fwnode_provider(&xgene_msi_get_fwnode);
> +#endif
>  	return 0;
>  }
>  
> @@ -449,6 +460,13 @@ static int xgene_msi_hwirq_free(unsigned int cpu)
>  	{},
>  };
>  
> +#ifdef CONFIG_ACPI
> +static const struct acpi_device_id xgene_msi_acpi_ids[] = {
> +	{"APMC0D0E", 0},
> +	{ },
> +};
> +#endif
> +
>  static int xgene_msi_probe(struct platform_device *pdev)
>  {
>  	struct resource *res;
> @@ -469,7 +487,17 @@ static int xgene_msi_probe(struct platform_device *pdev)
>  		goto error;
>  	}
>  	xgene_msi->msi_addr = res->start;
> -	xgene_msi->node = pdev->dev.of_node;
> +
> +	xgene_msi->fwnode = of_node_to_fwnode(pdev->dev.of_node);
> +	if (!xgene_msi->fwnode) {
> +		xgene_msi->fwnode = irq_domain_alloc_fwnode(NULL);

Please provide something other than NULL, such as the base address if
the device. That's quite useful for debugging.

> +		if (!xgene_msi->fwnode) {
> +			dev_err(&pdev->dev, "Failed to create fwnode\n");
> +			rc = ENOMEM;
> +			goto error;
> +		}
> +	}
> +
>  	xgene_msi->num_cpus = num_possible_cpus();
>  
>  	rc = xgene_msi_init_allocator(xgene_msi);
> @@ -540,6 +568,7 @@ static int xgene_msi_probe(struct platform_device *pdev)
>  	.driver = {
>  		.name = "xgene-msi",
>  		.of_match_table = xgene_msi_match_table,
> +		.acpi_match_table = ACPI_PTR(xgene_msi_acpi_ids),
>  	},
>  	.probe = xgene_msi_probe,
>  	.remove = xgene_msi_remove,
> 

The code is trivial, but relies on the MSI controller to probe before
the PCI bus. What enforces this? How is it making sure that this is not
going to break in the next kernel release? As far as I can tell, there
is no explicit dependency between the two, making it the whole thing
extremely fragile.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...