linux-kernel - [PATCH v2] dmaengine: qcom: bam_dma: convert tasklet to a BH workqueue

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Message-Id: <20251219-bam-dma-bh-workqueue-v2-1-ed5eeab78cf0@oss.qualcomm.com>
Date: Fri, 19 Dec 2025 10:46:40 +0100
From: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
To: Vinod Koul <vkoul@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
Subject: [PATCH v2] dmaengine: qcom: bam_dma: convert tasklet to a BH
 workqueue

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@...nel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Reviewed-by: Bjorn Andersson <andersson@...nel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
---
Tested with the Qualcomm Crypto Engine with no impact on stability or
performance (according to cryptsetup benchmark).

Changes in v2:
- Use the high-priority BH workqueue
- Link to v1: https://lore.kernel.org/all/20251106-qcom-bam-dma-refactor-v1-0-0e2baaf3d81a@linaro.org/
---
 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 bcd8de9a9a12621a36b49c31bff96f474468be06..509d9296f6d7ef7662325e39fa12b6db45badbec 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;
 };
 
 /**
@@ -869,7 +870,7 @@ 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);
@@ -899,9 +900,9 @@ 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)
@@ -1097,14 +1098,14 @@ 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;
 
@@ -1117,14 +1118,13 @@ 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)
 {
@@ -1292,14 +1292,14 @@ 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 */
@@ -1364,8 +1364,8 @@ 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);
 
@@ -1399,7 +1399,7 @@ 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);
 }

---
base-commit: 970d7fed472fd561d12773ff445497f847b7161d
change-id: 20251218-bam-dma-bh-workqueue-0d80ec0b6392

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>