Re: [PATCH v8 20/24] blk-mq: add scatterlist-less DMA mapping helpers

[ALOK TIWARI <alok.a.tiwari@oracle.com>]

> + * Start DMA mapping @req to @dma_dev.  @state and @iter are provided by the
> + * caller and don't need to be initialized.  @state needs to be stored for use
> + * at unmap time, @iter is only needed at map time.
> + *
> + * Returns %false if there is no segment to map, including due to an error, or
> + * %true it it did map a segment.

typo - it it -> if it

> + *
> + * If a segment was mapped, the DMA address for it is returned in @iter.addr and
> + * the length in @iter.len.  If no segment was mapped the status code is
> + * returned in @iter.status.
> + *
> + * The caller can call blk_rq_dma_map_coalesce() to check if further segments
> + * need to be mapped after this, or go straight to blk_rq_dma_map_iter_next()
> + * to try to map the following segments.
> + */
> +bool blk_rq_dma_map_iter_start(struct request *req, struct device *dma_dev,
> +		struct dma_iova_state *state, struct blk_dma_iter *iter)
> +{
> +	unsigned int total_len = blk_rq_payload_bytes(req);
> +	struct phys_vec vec;
> +
> +	iter->iter.bio = req->bio;
> +	iter->iter.iter = req->bio->bi_iter;
> +	memset(&iter->p2pdma, 0, sizeof(iter->p2pdma));
> +	iter->status = BLK_STS_OK;
> +
> +	/*
> +	 * Grab the first segment ASAP because we'll need it to check for P2P
> +	 * transfers.
> +	 */
> +	if (!blk_map_iter_next(req, &iter->iter, &vec))
> +		return false;
> +
> +	if (IS_ENABLED(CONFIG_PCI_P2PDMA) && (req->cmd_flags & REQ_P2PDMA)) {
> +		switch (pci_p2pdma_state(&iter->p2pdma, dma_dev,
> +				blk_phys_to_page(vec.paddr))) {
> +		case PCI_P2PDMA_MAP_BUS_ADDR:
> +			return blk_dma_map_bus(req, dma_dev, iter, &vec);
> +		case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +			/*
> +			 * P2P transfers through the host bridge are treated the
> +			 * same as non-P2P transfers below and during unmap.
> +			 */
> +			req->cmd_flags &= ~REQ_P2PDMA;
> +			break;
> +		default:
> +			iter->status = BLK_STS_INVAL;
> +			return false;
> +		}
> +	}
> +
> +	if (blk_can_dma_map_iova(req, dma_dev) &&
> +	    dma_iova_try_alloc(dma_dev, state, vec.paddr, total_len))
> +		return blk_rq_dma_map_iova(req, dma_dev, state, iter, &vec);
> +	return blk_dma_map_direct(req, dma_dev, iter, &vec);
> +}
> +EXPORT_SYMBOL_GPL(blk_rq_dma_map_iter_start);
> +
> +/**
> + * blk_rq_dma_map_iter_next - map the next DMA segment for a request
> + * @req:	request to map
> + * @dma_dev:	device to map to
> + * @state:	DMA IOVA state
> + * @iter:	block layer DMA iterator
> + *
> + * Iterate to the next mapping after a previous call to
> + * blk_rq_dma_map_iter_start().  See there for a detailed description of the
> + * arguments.
> + *
> + * Returns %false if there is no segment to map, including due to an error, or
> + * %true it it did map a segment.

typo - it it -> if it

> + *
> + * If a segment was mapped, the DMA address for it is returned in @iter.addr and
> + * the length in @iter.len.  If no segment was mapped the status code is
> + * returned in @iter.status.
> + */
> +bool blk_rq_dma_map_iter_next(struct request *req, struct device *dma_dev,
> +		struct dma_iova_state *state, struct blk_dma_iter *iter)
> +{
> +	struct phys_vec vec;
> +
> +	if (!blk_map_iter_next(req, &iter->iter, &vec))
> +		return false;
> +
> +	if (iter->p2pdma.map == PCI_P2PDMA_MAP_BUS_ADDR)
> +		return blk_dma_map_bus(req, dma_dev, iter, &vec);
> +	return blk_dma_map_direct(req, dma_dev, iter, &vec);
> +}
> +EXPORT_SYMBOL_GPL(blk_rq_dma_map_iter_next);
> +
>   static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
>   		struct scatterlist *sglist)
>   {
> diff --git a/include/linux/blk-mq-dma.h b/include/linux/blk-mq-dma.h
> new file mode 100644
> index 000000000000..588dc3c1ad1f
> --- /dev/null
> +++ b/include/linux/blk-mq-dma.h
> @@ -0,0 +1,62 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef BLK_MQ_DMA_H
> +#define BLK_MQ_DMA_H
> +
> +#include <linux/blk-mq.h>
> +#include <linux/pci-p2pdma.h>
> +
> +struct blk_dma_iter {
> +	/* Output address range for this iteration */
> +	dma_addr_t			addr;
> +	u32				len;
> +
> +	/* Status code. Only valid when blk_rq_dma_map_iter_* returned false */
> +	blk_status_t			status;
> +
> +	/* Internal to blk_rq_dma_map_iter_* */
> +	struct req_iterator		iter;
> +	struct pci_p2pdma_map_state	p2pdma;
> +};
> +
> +bool blk_rq_dma_map_iter_start(struct request *req, struct device *dma_dev,
> +		struct dma_iova_state *state, struct blk_dma_iter *iter);
> +bool blk_rq_dma_map_iter_next(struct request *req, struct device *dma_dev,
> +		struct dma_iova_state *state, struct blk_dma_iter *iter);
> +
> +/**
> + * blk_rq_dma_map_coalesce - were all segments coalesced?
> + * @state: DMA state to check
> + *
> + * Returns true if blk_rq_dma_map_iter_start coalesced all segments into a
> + * single DMA range.
> + */
> +static inline bool blk_rq_dma_map_coalesce(struct dma_iova_state *state)
> +{
> +	return dma_use_iova(state);
> +}
> +
> +/**
> + * blk_rq_dma_map_coalesce - try to DMA unmap a request
> + * @req:	request to unmap
> + * @dma_dev:	device to unmap from
> + * @state:	DMA IOVA state
> + * @mapped_len: number of bytes to unmap
> + *
> + * Returns %false if the callers needs to manually unmap every DMA segment

typo needs -> need

> + * mapped using @iter or %true if no work is left to be done.
> + */


Thanks,
Alok