Re: [PATCH] hw/char/bcm2835_aux: Fix incorrect interrupt ID when RX disabled

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 28/3/25 13:37, Chung-Yi Chen wrote:
> This patch fixes a misconfiguration issue in the read implementation of
> the AUX_MU_IIR_REG register. This issue can lead to a transmit interrupt
> being incorrectly interpreted as a receive interrupt when the receive
> interrupt is disabled and the receive FIFO holds valid bytes.
> 
> The AUX_MU_IIR_REG register (interrupt ID bits [2:1]) indicates the
> status of mini UART interrupts:
> 
>      - 00: No interrupts
>      - 01: Transmit FIFO is empty
>      - 10: Receive FIFO is not empty
>      - 11: <Not possible>
> 
> When the transmit interrupt is enabled and the receive interrupt is
> disabled, the original code incorrectly sets the interrupt ID bits.
> Specifically:
> 
>      1. Transmit FIFO empty, receive FIFO empty
>          - Expected 0b01, returned 0b01 (correct)
>      2. Transmit FIFO empty, receive FIFO not empty
>          - Expected 0b01, returned 0b10 (incorrect)
> 
> In the second case, the code sets the interrupt ID to 0b10 (receive FIFO
> is not empty) even if the receive interrupt is disabled.
> 
> To fix this, the patch adds additional condition for setting the
> interrupt ID bits to also check if the receive interrupt is enabled.
> 
> Reference: BCM2835 ARM Peripherals, page 13. Available on
> https://datasheets.raspberrypi.com/bcm2835/bcm2835-peripherals.pdf
> 
> Signed-off-by: Chung-Yi Chen <yeechen0207@gmail.com>
> ---
>   hw/char/bcm2835_aux.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Fixes: 97398d900ca ("bcm2835_aux: add emulation of BCM2835 AUX (aka 
UART1) block")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>