[xen master] xen/drivers/char/cadence-uart: fix IRQ registration failure propagation

[patchbot@xxxxxxx]

commit d075ab7f255a0cd50a778693a9c7743941b13eea
Author:     Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>
AuthorDate: Thu Apr 23 16:11:42 2026 +0000
Commit:     Michal Orzel <michal.orzel@xxxxxxx>
CommitDate: Mon Apr 27 08:52:38 2026 +0200

    xen/drivers/char/cadence-uart: fix IRQ registration failure propagation
    
    In cuart_init_postirq(), two code paths could reach the
    interrupt-enable write to IER without a handler being registered:
    
    - When no valid IRQ number was provided (uart->irq <= 0), the original
      positive-condition guard (if uart->irq > 0) skipped the irqaction
      setup but still fell through to the IER write, enabling the receive
      data interrupt with no handler installed.
    
    - When setup_irq() returned an error, only an error message was
      printed and execution continued to the IER write, arming the
      receive hardware interrupt line with no handler to service it. On
      platforms where the GIC receives this asserted line, the result is
      either repeated spurious-interrupt warnings or an unhandled
      interrupt fault.
    
    Restructure cuart_init_postirq() to use early returns in both error
    paths.
    
    Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
    Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
    Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 xen/drivers/char/cadence-uart.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/xen/drivers/char/cadence-uart.c b/xen/drivers/char/cadence-uart.c
index b2f379833f..0f1c3dd461 100644
--- a/xen/drivers/char/cadence-uart.c
+++ b/xen/drivers/char/cadence-uart.c
@@ -72,19 +72,25 @@ static void __init cuart_init_postirq(struct serial_port 
*port)
     struct cuart *uart = port->uart;
     int rc;
 
-    if ( uart->irq > 0 )
-    {
-        uart->irqaction.handler = cuart_interrupt;
-        uart->irqaction.name    = "cadence-uart";
-        uart->irqaction.dev_id  = port;
-        if ( (rc = setup_irq(uart->irq, 0, &uart->irqaction)) != 0 )
-            printk("ERROR: Failed to allocate cadence-uart IRQ %d\n", 
uart->irq);
-    }
+    /* Don't unmask interrupts if no valid irq was provided */
+    if ( uart->irq == 0 )
+        return;
+
+    uart->irqaction.handler = cuart_interrupt;
+    uart->irqaction.name    = "cadence-uart";
+    uart->irqaction.dev_id  = port;
 
     /* Clear pending error interrupts */
     cuart_write(uart, R_UART_RTRIG, 1);
     cuart_write(uart, R_UART_CISR, ~0);
 
+    if ( (rc = setup_irq(uart->irq, 0, &uart->irqaction)) != 0 )
+    {
+        printk("ERROR: Failed to allocate cadence-uart IRQ %u\n", uart->irq);
+        /* Do not unmask interrupts if irq handler wasn't set */
+        return;
+    }
+
     /* Unmask interrupts */
     cuart_write(uart, R_UART_IDR, ~0);
     cuart_write(uart, R_UART_IER, UART_SR_INTR_RTRIG);
--
generated by git-patchbot for /home/xen/git/xen.git#master