On Mon, Jan 15, 2024 at 08:02:56PM +0530, Vidya Sagar wrote: > > > On 1/12/2024 10:28 PM, Bjorn Helgaas wrote: > > External email: Use caution opening links or attachments > > > > > > 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@xxxxxxxxx> > > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx> > > > --- > > > V2: > > > * Addressed issues reported by kernel test robot <lkp@xxxxxxxxx> > > > > > > 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. > My understanding is that pci_host_common_probe() is mainly used in > systems where the firmware would have taken care of all the platform > specific initialization and giving the ECAM and 'ranges' info through DT > for the Linux kernel to go ahead and perform the enumeration. This is > similar to ACPI way of handing over the system from firmware to the OS. > > If PCIe controllers are getting initialized in the kernel itself, then > pci_host_probe() is called directly from the respective host controller > drivers which is the case with all the DesignWare based implementations > including Tegra194 and Tegra234. In those systems, since the controllers > themselves have come up and gotten initialized in the kernel, resource > assignment has to happen anyway. > > > > > 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 :) > Honestly I would have liked to repurpose of_pci_check_probe_only() API > to look for "preserve-boot-config" in the respective PCIe controller's > DT node and not "linux,pci-probe-only" in the chosen entry, had it not > for the single usage of of_pci_check_probe_only() in arch/powerpc > /platforms/pseries/setup.c file. > Also FWIW, "linux,pci-probe-only" is not documented anywhere. Yes, it is[1]. > > Since there is at least one user for of_pci_check_probe_only(), and > combining with the fact that the scope where "linux,pci-probe-only" and > "preserve-boot-config" are used (i.e. chosen entry Vs individual PCIe > controller node), I prefer to have it as a separate option. > Rob, please let me know if you have any strong objections to that? Didn't I already object? What's the concern with existing users? There shouldn't be any. If "linux,pci-probe-only" appeared in a bridge node, it would have been ignored and now would be honored. Rob [1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/chosen.yaml#L140
