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Re: [PATCH v2 1/4] xen/drivers/char: fix SCIF IRQ registration failure propagation
- To: Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Thu, 9 Apr 2026 16:31:58 +0200
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- Cc: Bertrand Marquis <bertrand.marquis@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "Volodymyr Babchuk" <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 09 Apr 2026 14:32:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09/04/2026 15:50, Oleksii Moisieiev wrote:
> In scif_uart_init_postirq(), when setup_irq() returns an error the
> failure was only logged via dprintk() and execution continued,
> unconditionally writing TIE|RIE|REIE into the Serial Control Register
> (SCSCR). This armed all three hardware interrupt lines (TX FIFO empty,
> RX data ready, receive error) with no handler registered to service
> them. On platforms where the GIC receives these asserted lines, the
> result is either repeated spurious-interrupt warnings or an unhandled
> interrupt fault.
>
> The fix adds an early return inside the error branch. The
> interrupt-enable write to SCSCR is skipped entirely when no handler is
> registered.
>
> SCIF TX continues to operate correctly after this change. The Xen
> serial framework never calls serial_async_transmit() for SCIF, so
> port->txbuf is always NULL. This causes __serial_putc() to take the
> synchronous finite-capacity path, which polls the SCFSR_TDFE hardware
> flag directly and does not depend on the interrupt mechanism. RX
> wouldn't work if irq wasn't registered.
>
> As a secondary clean-up, the hardware error-flag clearing sequence is
> moved to before the setup_irq() call so that error bits accumulated
> since init_preirq() are cleared unconditionally, regardless of whether
> IRQ registration succeeds.
>
> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
~Michal
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