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

[Manivannan Sadhasivam]

On Tue, Mar 10, 2026 at 04:44:16PM +0100, Bartosz Golaszewski wrote:
> 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@xxxxxxxxxx>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> Reviewed-by: Bjorn Andersson <andersson@xxxxxxxxxx>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>

Reviewed-by: Manivannan Sadhasivam <mani@xxxxxxxxxx>

- Mani

> ---
>  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
> 

-- 
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