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Date:   Fri, 12 Mar 2021 18:32:20 -0800
From:   Ira Weiny <ira.weiny@intel.com>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-mm@kvack.org, iommu@lists.linux-foundation.org,
        Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Ira Weiny <iweiny@intel.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jakowski Andrzej <andrzej.jakowski@intel.com>,
        Minturn Dave B <dave.b.minturn@intel.com>,
        Jason Ekstrand <jason@jlekstrand.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>
Subject: Re: [RFC PATCH v2 04/11] PCI/P2PDMA: Introduce
 pci_p2pdma_should_map_bus() and pci_p2pdma_bus_offset()
Message-ID: <20210313023220.GB3402637@iweiny-DESK2.sc.intel.com>
References: <20210311233142.7900-1-logang@deltatee.com>
 <20210311233142.7900-5-logang@deltatee.com>
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On Thu, Mar 11, 2021 at 04:31:34PM -0700, Logan Gunthorpe wrote:
> Introduce pci_p2pdma_should_map_bus() which is meant to be called by
            ^^^^^^^^^^^^^^^^^^^^^^^^^
	    pci_p2pdma_dma_map_type() ???

FWIW I find this name confusing with pci_p2pdma_map_type() and looking at the
implementation I'm not clear why pci_p2pdma_dma_map_type() needs to exist?

Ira

[snip]

> +
> +/**
> + * pci_p2pdma_dma_map_type - determine if a DMA mapping should use the
> + *	bus address, be mapped normally or fail
> + * @dev: device doing the DMA request
> + * @pgmap: dev_pagemap structure for the mapping
> + *
> + * Returns:
> + *    1 - if the page should be mapped with a bus address,
> + *    0 - if the page should be mapped normally through an IOMMU mapping or
> + *        physical address; or
> + *   -1 - if the device should not map the pages and an error should be
> + *        returned
> + */
> +int pci_p2pdma_dma_map_type(struct device *dev, struct dev_pagemap *pgmap)
> +{
> +	struct pci_p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(pgmap);
> +	struct pci_dev *client;
> +
> +	if (!dev_is_pci(dev))
> +		return -1;
> +
> +	client = to_pci_dev(dev);
> +
> +	switch (pci_p2pdma_map_type(p2p_pgmap->provider, client)) {
> +	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +		return 0;
> +	case PCI_P2PDMA_MAP_BUS_ADDR:
> +		return 1;
> +	default:
> +		return -1;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_dma_map_type);

I guess the main point here is to export this to the DMA layer?

Ira