[PATCH v12 02/12] dmaengine: qcom: bam_dma: convert tasklet to a BH workqueue

Bartosz Golaszewski
2026-03-10T15:44:51Z

BH workqueues are a modern mechanism, aiming to replace legacy tasklets.
Let's convert the BAM DMA driver to using the high-priority variant of
the BH workqueue.

[Vinod: suggested using the BG workqueue instead of the regular one
running in process context]

Suggested-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
drivers/dma/qcom/bam_dma.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index 19116295f8325767a0d97a7848077885b118241c..c8601bac555edf1bb4384fd39cb3449ec6e86334 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -42,6 +42,7 @@
#include <linux/pm_runtime.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
+#include <linux/workqueue.h>

#include "../dmaengine.h"
#include "../virt-dma.h"
@@ -397,8 +398,8 @@ struct bam_device {
struct clk *bamclk;
int irq;

- /* dma start transaction tasklet */
- struct tasklet_struct task;
+ /* dma start transaction workqueue */
+ struct work_struct work;
};

/**
@@ -863,7 +864,7 @@ static u32 process_channel_irqs(struct bam_device *bdev)
/*
* if complete, process cookie. Otherwise
* push back to front of desc_issued so that
- * it gets restarted by the tasklet
+ * it gets restarted by the work queue.
*/
if (!async_desc->num_desc) {
vchan_cookie_complete(&async_desc->vd);
@@ -893,9 +894,9 @@ static irqreturn_t bam_dma_irq(int irq, void *data)

srcs |= process_channel_irqs(bdev);

- /* kick off tasklet to start next dma transfer */
+ /* kick off the work queue to start next dma transfer */
if (srcs & P_IRQ)
- tasklet_schedule(&bdev->task);
+ queue_work(system_bh_highpri_wq, &bdev->work);

ret = pm_runtime_get_sync(bdev->dev);
if (ret < 0)
@@ -1091,14 +1092,14 @@ static void bam_start_dma(struct bam_chan *bchan)
}

/**
- * dma_tasklet - DMA IRQ tasklet
- * @t: tasklet argument (bam controller structure)
+ * bam_dma_work() - DMA interrupt work queue callback
+ * @work: work queue struct embedded in the BAM controller device struct
*
* Sets up next DMA operation and then processes all completed transactions
*/
-static void dma_tasklet(struct tasklet_struct *t)
+static void bam_dma_work(struct work_struct *work)
{
- struct bam_device *bdev = from_tasklet(bdev, t, task);
+ struct bam_device *bdev = from_work(bdev, work, work);
struct bam_chan *bchan;
unsigned int i;

@@ -1111,14 +1112,13 @@ static void dma_tasklet(struct tasklet_struct *t)
if (!list_empty(&bchan->vc.desc_issued) && !IS_BUSY(bchan))
bam_start_dma(bchan);
}
-
}

/**
* bam_issue_pending - starts pending transactions
* @chan: dma channel
*
- * Calls tasklet directly which in turn starts any pending transactions
+ * Calls work queue directly which in turn starts any pending transactions
*/
static void bam_issue_pending(struct dma_chan *chan)
{
@@ -1286,14 +1286,14 @@ static int bam_dma_probe(struct platform_device *pdev)
if (ret)
goto err_disable_clk;

- tasklet_setup(&bdev->task, dma_tasklet);
+ INIT_WORK(&bdev->work, bam_dma_work);

bdev->channels = devm_kcalloc(bdev->dev, bdev->num_channels,
sizeof(*bdev->channels), GFP_KERNEL);

if (!bdev->channels) {
ret = -ENOMEM;
- goto err_tasklet_kill;
+ goto err_workqueue_cancel;
}

/* allocate and initialize channels */
@@ -1358,8 +1358,8 @@ static int bam_dma_probe(struct platform_device *pdev)
err_bam_channel_exit:
for (i = 0; i < bdev->num_channels; i++)
tasklet_kill(&bdev->channels[i].vc.task);
-err_tasklet_kill:
- tasklet_kill(&bdev->task);
+err_workqueue_cancel:
+ cancel_work_sync(&bdev->work);
err_disable_clk:
clk_disable_unprepare(bdev->bamclk);

@@ -1393,7 +1393,7 @@ static void bam_dma_remove(struct platform_device *pdev)
bdev->channels[i].fifo_phys);
}

- tasklet_kill(&bdev->task);
+ cancel_work_sync(&bdev->work);

clk_disable_unprepare(bdev->bamclk);
}

--
2.47.3