Re: [PATCH 2/2] tty: serial: qcom-geni-serial: check for valid size before starting dma

[Konrad Dybcio]

On 7.03.2023 16:55, Srinivas Kandagatla wrote:
> Check if there are valid length of bytes to transfer before starting dma.
> 
> without this check we can see below kernel warning when we try to map a zero size buffers.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 0 at drivers/iommu/dma-iommu.c:1046 iommu_dma_unmap_page+0xe0/0xfc
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W          6.3.0-rc1-dirty #347
> Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
> pstate: 804000c5 (Nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : iommu_dma_unmap_page+0xe0/0xfc
> lr : iommu_dma_unmap_page+0x38/0xfc
> ...
> Call trace:
>  iommu_dma_unmap_page+0xe0/0xfc
>  dma_unmap_page_attrs+0x30/0x1ec
>  geni_se_tx_dma_unprep+0x58/0x80
>  qcom_geni_serial_isr+0x350/0x750
>  __handle_irq_event_percpu+0x58/0x148
>  handle_irq_event_percpu+0x18/0x4c
>  handle_irq_event+0x48/0x88
>  handle_fasteoi_irq+0xb0/0x130
>  generic_handle_domain_irq+0x2c/0x44
>  gic_handle_irq+0xd4/0x140
>  call_on_irq_stack+0x24/0x4c
>  do_interrupt_handler+0x80/0x84
>  el1_interrupt+0x38/0x6c
>  el1h_64_irq_handler+0x18/0x24
>  el1h_64_irq+0x64/0x68
>  cpuidle_enter_state+0x1e4/0x310
>  cpuidle_enter+0x3c/0x54
>  call_cpuidle+0x1c/0x40
>  do_idle+0x204/0x260
>  cpu_startup_entry+0x28/0x2c
>  kernel_init+0x0/0x12c
>  arch_post_acpi_subsys_init+0x0/0x8
>  start_kernel+0x3cc/0x74c
>  __primary_switched+0xbc/0xc4
> 
> Fixes: 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
S-o-b but no C-d-b? Weird..

> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> ---
Anyway, the change is good!

Reviewed-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>

Konrad
>  drivers/tty/serial/qcom_geni_serial.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 5972b5c317d3..bb63a00f4c07 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -637,6 +637,9 @@ static void qcom_geni_serial_start_tx_dma(struct uart_port *uport)
>  
>  	xmit_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
>  
> +	if (!xmit_size)
> +		return;
> +
>  	qcom_geni_serial_setup_tx(uport, xmit_size);
>  
>  	ret = geni_se_tx_dma_prep(&port->se, &xmit->buf[xmit->tail],