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 16:48:26 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>, agross@...nel.org,
        andersson@...nel.org, gregkh@...uxfoundation.org
Cc:     jirislaby@...nel.org, bartosz.golaszewski@...aro.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 07/03/2023 16:20, Konrad Dybcio 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..
> 
Yes, I did mess up this part.
thanks for spotting this, Will fix this in next spin!

--srini
>> 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],