[PATCH v2 1/2] ns16550: reject IRQ above nr_irqs_gsi

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

Intel LPSS has INTERRUPT_LINE set to 0xff by default, that can't
possibly work. While a proper IRQ configuration may be useful,
validating value retrieved from the hardware is still necessary. If it
fails, use the device in poll mode, instead of crashing down the line
(at smp_initr_init()). Currently it's
x86-specific, as the surrounding code is guarded with CONFIG_X86 anyway.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
Changes in v2:
 - add log message
 - extend commit message
 - code style fix
---
 xen/drivers/char/ns16550.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index fb75cee4a13a..0c6f6ec43de1 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -1238,6 +1238,15 @@ pci_uart_config(struct ns16550 *uart, bool_t skip_amt, 
unsigned int idx)
                             pci_conf_read8(PCI_SBDF(0, b, d, f),
                                            PCI_INTERRUPT_LINE) : 0;
 
+                if ( uart->irq >= nr_irqs_gsi )
+                {
+                    printk(XENLOG_WARNING
+                           "ns16550: %02x:%02x.%u reports invalid IRQ %d, "
+                           "falling back to a poll mode\n",
+                           b, d, f, uart->irq);
+                    uart->irq = 0;
+                }
+
                 return 0;
             }
         }
-- 
2.35.1