Re: [PATCH v20 6/9] PCI: Cache PCI DSN into pci_dev->dsn during probe

["Cheatham, Benjamin" <benjamin.cheatham@amd.com>]

On 9/2/2026 8:39 AM, Terry Bowman wrote:
> Subsequent CXL error-reporting code paths need to log the PCI Device
> Serial Number (DSN) as part of trace events emitted from interrupt or
> panic context. Computing the DSN there via pci_get_dsn() requires PCI
> configuration space reads, which are slow, can fail when the link is
> down or frozen, and may not be safe in some contexts.
> 
> Add a u64 dsn field to struct pci_dev and populate it from pci_get_dsn()
> during pci_init_capabilities() at probe time via pci_dsn_init(). Only
> write dev->dsn when the read succeeds. The zero initial value from
> pci_dev allocation already represents 'no DSN available.'
> 
> Remove the now-redundant dsn member from the pciehp struct controller
> along with its kernel-doc. Drop the pci_get_slot()/pci_dev_put() pairs
> in pciehp_configure_device() and pcie_init() that existed solely to
> read the DSN into ctrl->dsn. Use pdev->dsn in pciehp_device_replaced()
> for the device-replacement comparison.
> 
> pci_get_dsn() is not modified because it remains a pure config-space read
> with no side effects on pci_dev. The cache is written exclusively by
> pci_dsn_init() at probe time.
> 
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
> 
> ---

Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>