The existing "linux,pci-probe-only" property applies at a system level
and it is not possible to selectively convey individual host bridge's
requirement w.r.t preserving the boot configuration done by the platform
firmware to the kernel. "preserve-boot-config" addresses that concern
and can be used to preserve the boot configuration for host bridges
selectivey.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V2:
* None

 Documentation/devicetree/bindings/pci/pci.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
index 6a8f2874a24d..0a5ff998cbe8 100644
--- a/Documentation/devicetree/bindings/pci/pci.txt
+++ b/Documentation/devicetree/bindings/pci/pci.txt
@@ -32,6 +32,10 @@ driver implementation may support the following properties:
    root port to downstream device and host bridge drivers can do programming
    which depends on CLKREQ signal existence. For example, programming root port
    not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
+- preserve-boot-config:
+   If present this property specifies that this host bridge is already
+   configured by the platform firmware and the OS doesn't need to reconfigure
+   it again.
 
 PCI-PCI Bridge properties
 -------------------------
-- 
2.25.1

On Wed, Jan 10, 2024 at 08:37:24AM +0530, Vidya Sagar wrote:
> The existing "linux,pci-probe-only" property applies at a system level
> and it is not possible to selectively convey individual host bridge's
> requirement w.r.t preserving the boot configuration done by the platform
> firmware to the kernel. "preserve-boot-config" addresses that concern
> and can be used to preserve the boot configuration for host bridges
> selectivey.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V2:
> * None
> 
>  Documentation/devicetree/bindings/pci/pci.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
> index 6a8f2874a24d..0a5ff998cbe8 100644
> --- a/Documentation/devicetree/bindings/pci/pci.txt
> +++ b/Documentation/devicetree/bindings/pci/pci.txt
> @@ -32,6 +32,10 @@ driver implementation may support the following properties:
>     root port to downstream device and host bridge drivers can do programming
>     which depends on CLKREQ signal existence. For example, programming root port
>     not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
> +- preserve-boot-config:
> +   If present this property specifies that this host bridge is already
> +   configured by the platform firmware and the OS doesn't need to reconfigure
> +   it again.

Anything new must be a schema.

Don't create something new to workaround the problem. Extend the 
existing support. For this, make "linux,pci-probe-only" allowed in host 
bridge nodes. Yeah, there's the issue that this property sets a global 
flag, but I'd imagine the PCI maintainers would agree that some flags 
should/could be per bus.

Rob