From: Edward Pickup <Edward.Pickup@arm.com>

This patch adds a Xen boot arguments that, if enabled, causes a call to
existing code to scan pci devices enumerated by the firmware.

This will be needed ahead of dom0less support for pci passthrough on
arm.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Signed-off-by: Mykyta Poturai <mykyta_poturai@epam.com>
---
(cherry picked from commit bce463e1588a45e1bfdf59fc0d5f88b16604e439 from
 the downstream branch poc/pci-passthrough from
 https://gitlab.com/xen-project/people/bmarquis/xen-arm-poc.git)

v1->v2:
* remove is_pci_scan_enabled wrapper
* make pci_scan_enabled ro_after_init
* drop debug prints
* drop Edward's SOB

changes since cherry-pick:
* s/always_inline/inline/
* replace additional kconfig option with config DEBUG
---
 docs/misc/xen-command-line.pandoc  |  7 +++++++
 xen/arch/arm/include/asm/pci.h     |  3 +++
 xen/arch/arm/pci/pci-host-common.c |  1 +
 xen/arch/arm/pci/pci.c             | 24 ++++++++++++++++++++++--
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 518e42d965..4a66c5a8f9 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2072,6 +2072,13 @@ This option can be specified more than once (up to 8 times at present).
 
 Flag to enable or disable support for PCI passthrough
 
+### pci-scan (arm)
+> `= <boolean>`
+
+> Default: `false`
+
+Flag to enable or disable Xen PCI scan at boot.
+
 ### pcid (x86)
 > `= <boolean> | xpti=<bool>`
 
diff --git a/xen/arch/arm/include/asm/pci.h b/xen/arch/arm/include/asm/pci.h
index 08ffcd4438..7289f7688b 100644
--- a/xen/arch/arm/include/asm/pci.h
+++ b/xen/arch/arm/include/asm/pci.h
@@ -23,6 +23,7 @@
 #define pci_to_dev(pcidev) (&(pcidev)->arch.dev)
 
 extern bool pci_passthrough_enabled;
+extern bool pci_scan_enabled;
 
 struct rangeset;
 
@@ -155,6 +156,8 @@ bool arch_pci_device_physdevop(void);
 
 #else   /*!CONFIG_HAS_PCI*/
 
+#define pci_scan_enabled false
+
 struct pci_dev;
 
 static inline void arch_pci_init_pdev(struct pci_dev *pdev) {}
diff --git a/xen/arch/arm/pci/pci-host-common.c b/xen/arch/arm/pci/pci-host-common.c
index 487c545f3a..d3481b05eb 100644
--- a/xen/arch/arm/pci/pci-host-common.c
+++ b/xen/arch/arm/pci/pci-host-common.c
@@ -284,6 +284,7 @@ pci_host_common_probe(struct dt_device_node *dev,
     }
 
     pci_add_host_bridge(bridge);
+    pci_add_segment(bridge->segment);
 
     return bridge;
 
diff --git a/xen/arch/arm/pci/pci.c b/xen/arch/arm/pci/pci.c
index beb1f971fa..1b34e17517 100644
--- a/xen/arch/arm/pci/pci.c
+++ b/xen/arch/arm/pci/pci.c
@@ -91,8 +91,14 @@ bool arch_pci_device_physdevop(void)
 bool __read_mostly pci_passthrough_enabled;
 boolean_param("pci-passthrough", pci_passthrough_enabled);
 
+/* By default pci scan is disabled. */
+bool __ro_after_init pci_scan_enabled;
+boolean_param("pci-scan", pci_scan_enabled);
+
 static int __init pci_init(void)
 {
+    int ret;
+
     /*
      * Enable PCI passthrough when has been enabled explicitly
      * (pci-passthrough=on).
@@ -104,9 +110,23 @@ static int __init pci_init(void)
         panic("Could not initialize PCI segment 0\n");
 
     if ( acpi_disabled )
-        return dt_pci_init();
+        ret = dt_pci_init();
     else
-        return acpi_pci_init();
+        ret = acpi_pci_init();
+
+    if ( ret < 0 )
+        return ret;
+
+    if ( pci_scan_enabled )
+    {
+        ret = scan_pci_devices();
+
+        if ( ret < 0 )
+            return ret;
+
+    }
+
+    return 0;
 }
 __initcall(pci_init);
 
-- 
2.34.1

On 24.09.2025 09:59, Mykyta Poturai wrote:
> --- a/xen/arch/arm/include/asm/pci.h
> +++ b/xen/arch/arm/include/asm/pci.h
> @@ -23,6 +23,7 @@
>  #define pci_to_dev(pcidev) (&(pcidev)->arch.dev)
>  
>  extern bool pci_passthrough_enabled;
> +extern bool pci_scan_enabled;

At this point of the series this isn't needed, ...

> @@ -155,6 +156,8 @@ bool arch_pci_device_physdevop(void);
>  
>  #else   /*!CONFIG_HAS_PCI*/
>  
> +#define pci_scan_enabled false

... this is entirely unused, and ...

> --- a/xen/arch/arm/pci/pci.c
> +++ b/xen/arch/arm/pci/pci.c
> @@ -91,8 +91,14 @@ bool arch_pci_device_physdevop(void)
>  bool __read_mostly pci_passthrough_enabled;
>  boolean_param("pci-passthrough", pci_passthrough_enabled);
>  
> +/* By default pci scan is disabled. */
> +bool __ro_after_init pci_scan_enabled;

... and hence this wants to be static __initdata. Otherwise, strictly
speaking, this is "unreachable data" post-init as per Misra's unreachable
code criteria (which surely ought to extend to data as well).

> @@ -104,9 +110,23 @@ static int __init pci_init(void)
>          panic("Could not initialize PCI segment 0\n");
>  
>      if ( acpi_disabled )
> -        return dt_pci_init();
> +        ret = dt_pci_init();
>      else
> -        return acpi_pci_init();
> +        ret = acpi_pci_init();
> +
> +    if ( ret < 0 )
> +        return ret;

I understand this is merely transforming existing code, but I don't see
what actual use the returning of an error here and hence also ...

> +    if ( pci_scan_enabled )
> +    {
> +        ret = scan_pci_devices();
> +
> +        if ( ret < 0 )
> +            return ret;

... here has. The system will continue booting nevertheless, iirc without
even a diagnostic from caller.

Jan