linux-kernel - Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

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Message-ID: <20240112165830.GA2271982@bhelgaas>
Date: Fri, 12 Jan 2024 10:58:30 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, will@...nel.org, frowand.list@...il.com,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	treding@...dia.com, jonathanh@...dia.com, kthota@...dia.com,
	mmaddireddy@...dia.com, sagar.tv@...il.com,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config"
 property

On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
> Add support for "preserve-boot-config" property that can be used to
> selectively (i.e. per host bridge) instruct the kernel to preserve the
> boot time configuration done by the platform firmware.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> V2:
> * Addressed issues reported by kernel test robot <lkp@...el.com>
> 
>  drivers/pci/controller/pci-host-common.c |  5 ++++-
>  drivers/pci/of.c                         | 18 ++++++++++++++++++
>  drivers/pci/probe.c                      |  2 +-
>  include/linux/of_pci.h                   |  6 ++++++
>  4 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index 6be3266cd7b5..d3475dc9ec44 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
>  
>  	of_pci_check_probe_only();
>  
> +	bridge->preserve_config =
> +		of_pci_check_preserve_boot_config(dev->of_node);

Thanks for leveraging the existing "preserve_config" support for the
ACPI _DSM.  Is pci_host_common_probe() the best place for this?  I
think there are many DT platform drivers that do not use
pci_host_common_probe(), so I wonder if there's a more generic place
to put this.

I see Rob's concern about adding "preserve-boot-config" vs extending
"linux,pci-probe-only" and I don't really have an opinion on that,
although I do think the "pci-probe-only" name is not as descriptive as
it could be.  I guess somebody will argue that "preserve_config" could
be more descriptive, too :)

Bjorn