[PATCH] cxl/port: Fix endpoint RAS error unmasking

[Richard Cheng <icheng@nvidia.com>]

Commit dab7162d0ae7 ("cxl/port: Move endpoint component register
management to cxl_port") moved EP RAS handling from cxl_pci to cxl_port,
while cxl_ras_unmask() have the assumption that port->uport_dev is a PCI
device.
If the topology use cxl_memdev as uport_dev, the PCI check will fail and
CXL RAS masks remain set.

Resolve memdev uports to their parent dev and verify the device is PCI.

Fixes: dab7162d0ae7 ("cxl/port: Move endpoint component register management to cxl_port")
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
Reproducer is a QEMU Type-3 guest

1. Ensure no CXL region is active and PCIe AER is enabled.
2. Restore the emulated RAS registers to their reset masks.
3. Reprobe cxl_pci and read the masks again.

```
BDF=$(basename "$(dirname "$(readlink -f /sys/bus/cxl/devices/mem0)")")
BAR0=$(awk 'NR == 1 { print $1 }' /sys/bus/pci/devices/$BDF/resource)
UNC_MASK=$(printf '0x%x' $((BAR0 + 0x1084)))
COR_MASK=$(printf '0x%x' $((BAR0 + 0x1090)))

busybox devmem "$UNC_MASK" 32 0x1cfff
busybox devmem "$COR_MASK" 32 0x7f

echo "$BDF" > /sys/bus/pci/drivers/cxl_pci/unbind
echo "$BDF" > /sys/bus/pci/drivers/cxl_pci/bind
udevadm settle

busybox devmem "$UNC_MASK" 32
busybox devmem "$COR_MASK" 32
```

Before the fix, the masks remain 0x1cfff and 0x7f. After the fix,
both masks read as zero.

Best regards,
Richard Cheng.
---
 drivers/cxl/port.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
index c12fd0b89883..c48216e5078f 100644
--- a/drivers/cxl/port.c
+++ b/drivers/cxl/port.c
@@ -74,15 +74,18 @@ static int cxl_switch_port_probe(struct cxl_port *port)
 
 static int cxl_ras_unmask(struct cxl_port *port)
 {
+	struct device *host = port->uport_dev;
 	struct pci_dev *pdev;
 	void __iomem *addr;
 	u32 orig_val, val, mask;
 	u16 cap;
 	int rc;
 
-	if (!dev_is_pci(port->uport_dev))
+	if (is_cxl_memdev(host))
+		host = host->parent;
+	if (!host || !dev_is_pci(host))
 		return 0;
-	pdev = to_pci_dev(port->uport_dev);
+	pdev = to_pci_dev(host);
 
 	if (!port->regs.ras) {
 		pci_dbg(pdev, "No RAS registers.\n");

base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
-- 
2.43.0