PCI: Add PCIE_RESET_CONFIG_DEVICE_WAIT_MS waiting time value

Add the PCIE_RESET_CONFIG_DEVICE_WAIT_MS macro to define the minimum
waiting time between exit from a conventional reset and sending the
first configuration request to the device.

As described in PCIe r6.0, sec 6.6.1 <Conventional Reset>, there are two
different use cases of the value:

   - "With a Downstream Port that does not support Link speeds greater
     than 5.0 GT/s, software must wait a minimum of 100 ms following exit
     from a Conventional Reset before sending a Configuration Request to
     the device immediately below that Port."

   - "With a Downstream Port that supports Link speeds greater than
     5.0 GT/s, software must wait a minimum of 100 ms after Link training
     completes before sending a Configuration Request to the device
     immediately below that Port."

[kwilczynski: commit log]
Link: https://lore.kernel.org/linux-pci/20240328091835.14797-21-minda.chen@starfivetech.comSigned-off-by: Kevin Xie <kevin.xie@starfivetech.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mason Huo <mason.huo@starfivetech.com>

drivers/pci/pci.h

@@ -22,6 +22,21 @@
  */
 #define PCIE_PME_TO_L2_TIMEOUT_US	10000
 
+/*
+ * PCIe r6.0, sec 6.6.1 <Conventional Reset>
+ *
+ * - "With a Downstream Port that does not support Link speeds greater
+ *    than 5.0 GT/s, software must wait a minimum of 100 ms following exit
+ *    from a Conventional Reset before sending a Configuration Request to
+ *    the device immediately below that Port."
+ *
+ * - "With a Downstream Port that supports Link speeds greater than
+ *    5.0 GT/s, software must wait a minimum of 100 ms after Link training
+ *    completes before sending a Configuration Request to the device
+ *    immediately below that Port."
+ */
+#define PCIE_RESET_CONFIG_DEVICE_WAIT_MS	100
+
 extern const unsigned char pcie_link_speed[];
 extern bool pci_early_dump;