Re: [PATCH V2 1/2] dt-bindings: Add PCIe "preserve-boot-config" property

From: Rob Herring <robh@kernel.org>
To: Vidya Sagar <vidyas@nvidia.com>
Cc: lpieralisi@kernel.org, kw@linux.com, bhelgaas@google.com,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	will@kernel.org, frowand.list@gmail.com,
	linux-pci@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, treding@nvidia.com,
	jonathanh@nvidia.com, kthota@nvidia.com, mmaddireddy@nvidia.com,
	sagar.tv@gmail.com
Subject: Re: [PATCH V2 1/2] dt-bindings: Add PCIe "preserve-boot-config" property
Date: Fri, 12 Jan 2024 08:33:20 -0600	[thread overview]
Message-ID: <20240112143320.GA3143039-robh@kernel.org> (raw)
In-Reply-To: <20240110030725.710547-2-vidyas@nvidia.com>

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