PCI: Fix link speed calculation on retrain failure

When pcie_failed_link_retrain() fails to retrain, it tries to revert to the
previous link speed.  However it calculates that speed from the Link
Control 2 register without masking out non-speed bits first.

PCIE_LNKCTL2_TLS2SPEED() converts such incorrect values to
PCI_SPEED_UNKNOWN (0xff), which in turn causes a WARN splat in
pcie_set_target_speed():

  pci 0000:00:01.1: [1022:14ed] type 01 class 0x060400 PCIe Root Port
  pci 0000:00:01.1: broken device, retraining non-functional downstream link at 2.5GT/s
  pci 0000:00:01.1: retraining failed
  WARNING: CPU: 1 PID: 1 at drivers/pci/pcie/bwctrl.c:168 pcie_set_target_speed
  RDX: 0000000000000001 RSI: 00000000000000ff RDI: ffff9acd82efa000
  pcie_failed_link_retrain
  pci_device_add
  pci_scan_single_device

Mask out the non-speed bits in PCIE_LNKCTL2_TLS2SPEED() and
PCIE_LNKCAP_SLS2SPEED() so they don't incorrectly return PCI_SPEED_UNKNOWN.

Fixes: de9a6c8 ("PCI/bwctrl: Add pcie_set_target_speed() to set PCIe Link Speed")
Reported-by: Andrew <andreasx0@protonmail.com>
Closes: https://lore.kernel.org/r/7iNzXbCGpf8yUMJZBQjLdbjPcXrEJqBxy5-bHfppz0ek-h4_-G93b1KUrm106r2VNF2FV_sSq0nENv4RsRIUGnlYZMlQr2ZD2NyB5sdj5aU=@protonmail.com/
Suggested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiwei Sun <sunjw10@lenovo.com>
[bhelgaas: commit log, add details from https://lore.kernel.org/r/1c92ef6bcb314ee6977839b46b393282e4f52e74.1750684771.git.lukas@wunner.de]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: stable@vger.kernel.org	# v6.13+
Link: https://patch.msgid.link/20250123055155.22648-2-sjiwei@163.com

Author: Jiwei Sun

drivers/pci/pci.h

@@ -391,12 +391,14 @@ void pci_bus_put(struct pci_bus *bus);
 
 #define PCIE_LNKCAP_SLS2SPEED(lnkcap)					\
 ({									\
-	((lnkcap) == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT :	\
-	 (lnkcap) == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT :	\
-	 (lnkcap) == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT :	\
-	 (lnkcap) == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT :	\
-	 (lnkcap) == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT :	\
-	 (lnkcap) == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT :	\
+	u32 lnkcap_sls = (lnkcap) & PCI_EXP_LNKCAP_SLS;			\
+									\
+	(lnkcap_sls == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT :	\
+	 lnkcap_sls == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT :	\
+	 lnkcap_sls == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT :	\
+	 lnkcap_sls == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT :	\
+	 lnkcap_sls == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT :	\
+	 lnkcap_sls == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT :	\
 	 PCI_SPEED_UNKNOWN);						\
 })
 
@@ -411,13 +413,17 @@ void pci_bus_put(struct pci_bus *bus);
 	 PCI_SPEED_UNKNOWN)
 
 #define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
-	((lnkctl2) == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
-	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
-	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
-	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
-	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
-	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
-	 PCI_SPEED_UNKNOWN)
+({									\
+	u16 lnkctl2_tls = (lnkctl2) & PCI_EXP_LNKCTL2_TLS;		\
+									\
+	(lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT :	\
+	 lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT :	\
+	 lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT :	\
+	 lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT :	\
+	 lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT :	\
+	 lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT :	\
+	 PCI_SPEED_UNKNOWN);						\
+})
 
 /* PCIe speed to Mb/s reduced by encoding overhead */
 #define PCIE_SPEED2MBS_ENC(speed) \