Re: [RFC PATCH v4 5/6] drivers/migrate_offload: add DMA batch copy driver (dcbm)

[Gregory Price]

On Mon, Mar 09, 2026 at 12:07:31PM +0000, Shivank Garg wrote:
> diff --git a/drivers/migrate_offload/Kconfig b/drivers/migrate_offload/Kconfig
> new file mode 100644
> index 000000000000..0bbaedbae4ad
> --- /dev/null
> +++ b/drivers/migrate_offload/Kconfig
> @@ -0,0 +1,8 @@
> +config DCBM_DMA
> +	bool "DMA Core Batch Migrator"

Should this be tri-state or is built-in the only valid state?

> +static int setup_sg_tables(struct dma_work *work, struct list_head **src_pos,
> +		struct list_head **dst_pos, int nr)
> +{
... snip ..
> +	dev = dmaengine_get_dma_device(work->chan);
> +	if (!dev) {
> +		ret = -ENODEV;
> +		goto err_free_dst_table;
> +	}
> +	ret = dma_map_sgtable(dev, work->src_sgt, DMA_TO_DEVICE,
> +			DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING);
> +	if (ret)
> +		goto err_free_dst_table;
> +	ret = dma_map_sgtable(dev, work->dst_sgt, DMA_FROM_DEVICE,
> +			DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING);
> +	if (ret)
> +		goto err_unmap_src;
> +
> +	if (work->src_sgt->nents != work->dst_sgt->nents) {
> +		ret = -EINVAL;
> +		goto err_unmap_dst;
> +	}

Fairly new to dma space, but I thought the dma stuff could merge pages
on iommu systems. Wouldn't this check hit fairly often?

~Gregory