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

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Message-Id: <20230307155543.31021-2-srinivas.kandagatla@linaro.org>
Date:   Tue,  7 Mar 2023 15:55:42 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     agross@...nel.org, andersson@...nel.org, gregkh@...uxfoundation.org
Cc:     konrad.dybcio@...aro.org, jirislaby@...nel.org,
        bartosz.golaszewski@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: [PATCH 2/2] tty: serial: qcom-geni-serial: check for valid size before starting dma

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>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 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],
-- 
2.21.0