Re: [PATCH v5 1/3] PCI: Cache bridge firmware secondary bus number

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 11-Nov-26 4:18 AM, Mario Limonciello wrote:
> Bridge scans are split into two passes when bus numbers need reassigning.
> Save the firmware secondary bus number on the bridge pci_dev during pass 0,
> before the bridge is disabled, and keep it for pass 1 so devices discovered
> there can read the original bus number via their upstream bridge.
> 
> Guard the cached value with a validity flag so later rescans do not overwrite
> it with the renumbered runtime value.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>   drivers/pci/probe.c | 4 ++++
>   include/linux/pci.h | 3 +++
>   2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 27008e2ea5afc..14b3dd7dac271 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1418,6 +1418,10 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
>   
>   	pci_dbg(dev, "scanning [bus %02x-%02x] behind bridge, pass %d\n",
>   		secondary, subordinate, pass);
> +	if (!pass && !dev->fw_sec_busnr_valid) {
> +		dev->fw_sec_busnr = secondary;
> +		dev->fw_sec_busnr_valid = true;
> +	}

I think the original suggestion from Bjorn was to save it inside 
pci_read_bridge_windows() which happens before the two pass scan. In 
that case, it doesn't need the extra flag or checks.

Thanks,
Lijo

>   
>   	if (!primary && (primary != bus->number) && secondary && subordinate) {
>   		pci_warn(dev, "Primary bus is hard wired to 0\n");
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 5ffcf5ce8c966..b942dbb4edf57 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -363,6 +363,8 @@ struct pci_dev {
>   	struct pci_slot	*slot;		/* Physical slot this device is in */
>   
>   	unsigned int	devfn;		/* Encoded device & function index */
> +	/* Firmware secondary bus number saved across bridge scan passes */
> +	unsigned char	fw_sec_busnr;
>   	unsigned short	vendor;
>   	unsigned short	device;
>   	unsigned short	subsystem_vendor;
> @@ -414,6 +416,7 @@ struct pci_dev {
>   	unsigned int	pme_poll:1;	/* Poll device's PME status bit */
>   	unsigned int	pinned:1;	/* Whether this dev is pinned */
>   	unsigned int	config_rrs_sv:1; /* Config RRS software visibility */
> +	unsigned int	fw_sec_busnr_valid:1;
>   	unsigned int	imm_ready:1;	/* Supports Immediate Readiness */
>   	unsigned int	d1_support:1;	/* Low power state D1 is supported */
>   	unsigned int	d2_support:1;	/* Low power state D2 is supported */
>