Re: [PATCH v23 06/14] dmaengine: qcom: bam_dma: add support for BAM locking

Hi Bartosz,

On 7/21/2026 7:03 PM, Bartosz Golaszewski wrote:
[...]

> @@ -676,13 +691,26 @@ static void bam_free_chan(struct dma_chan *chan)
>   static int bam_slave_config(struct dma_chan *chan,
>   			    struct dma_slave_config *cfg)
>   {
> +	struct bam_config *peripheral_cfg = cfg->peripheral_config;
>   	struct bam_chan *bchan = to_bam_chan(chan);
> +	const struct bam_device_data *bdata = bchan->bdev->dev_data;
>   
>   	guard(spinlock_irqsave)(&bchan->vc.lock);
>   
>   	memcpy(&bchan->slave, cfg, sizeof(*cfg));
>   	bchan->reconfigure = 1;
>   
> +	/*
> +	 * This is required to setup the pipe locking and must be done even
> +	 * before the first call to bam_start_dma().
> +	 */
> +	if (bdata->pipe_lock_supported && peripheral_cfg) {
> +		if (cfg->direction != DMA_MEM_TO_DEV)
> +			return -EINVAL;
> +
> +		bchan->lock_scratchpad_addr = peripheral_cfg->lock_scratchpad_addr;
IIUC, peripheral_cfg will be filled by the client driver of BAM right ? 
if not, who actually passes it ?
> +	}
> +
>   	return 0;
>   }
>   
> @@ -802,6 +830,7 @@ static int bam_dma_terminate_all(struct dma_chan *chan)
>   		}

[...]

>   static void bam_start_dma(struct bam_chan *bchan)
>   {
> -	struct virt_dma_desc *vd = vchan_next_desc(&bchan->vc);
> +	struct virt_dma_desc *vd;
>   	struct bam_device *bdev = bchan->bdev;
>   	struct bam_async_desc *async_desc = NULL;
>   	struct bam_desc_hw *desc;
> @@ -1064,6 +1197,7 @@ static void bam_start_dma(struct bam_chan *bchan)
>   
>   	lockdep_assert_held(&bchan->vc.lock);
>   
> +	vd = vchan_next_desc(&bchan->vc);
>   	if (!vd)
>   		return;
>   
> @@ -1072,6 +1206,24 @@ static void bam_start_dma(struct bam_chan *bchan)
>   		return;
>   
>   	while (vd && !IS_BUSY(bchan)) {
> +		/*
> +		 * Open a LOCK/UNLOCK bracket around each fresh sequence.
> +		 * Sentinels inserted by bam_setup_pipe_lock() are skipped: they
> +		 * already have bam_locked set and must not trigger a second pair.
> +		 */
> +		if (!bchan->bam_locked) {
> +			ret = bam_setup_pipe_lock(bchan);
Hence, overall you meant to lock bam pipe once during the starting of 
the bam dma engine ? is it ?
> +			if (ret) {
> +				dev_err_ratelimited(bdev->dev,
> +					"failed to setup the pipe lock, deferring transfer: %d\n",
> +					ret);
> +				queue_work(system_bh_highpri_wq, &bdev->work);
> +				break;
> +			}
> +			if (bchan->bam_locked)
> +				vd = vchan_next_desc(&bchan->vc);
> +		}
> +
>   		list_del(&vd->node);
>   
>   		async_desc = container_of(vd, struct bam_async_desc, vd);
> @@ -1133,6 +1285,10 @@ static void bam_start_dma(struct bam_chan *bchan)
>   		bchan->tail += async_desc->xfer_len;
>   		bchan->tail %= MAX_DESCRIPTORS;
>   		list_add_tail(&async_desc->desc_node, &bchan->desc_list);
> +
> +		if (async_desc->is_lock_desc &&
> +		    (le16_to_cpu(async_desc->desc->flags) & DESC_FLAG_UNLOCK))
> +			bchan->bam_locked = false;
>   	}
>   
[...]