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

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Date:   Tue, 7 Mar 2023 17:43:47 +0100
From:   Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        agross@...nel.org, andersson@...nel.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tty: serial: qcom-geni-serial: check for valid size
 before starting dma

On Tue, 7 Mar 2023 at 17:20, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
>
>
> 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@...aro.org>
> S-o-b but no C-d-b? Weird..
>

It was supposed to be Reviewed-by actually.

Bart

> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> Anyway, the change is good!
>
> Reviewed-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>
> 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],