linux-kernel - Re: [RFC PATCH v2 07/11] dma-mapping: Add flags to dma_map

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Date:   Mon, 15 Mar 2021 10:33:13 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Ira Weiny <iweiny@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>
Subject: Re: [RFC PATCH v2 07/11] dma-mapping: Add flags to dma_map_ops to
 indicate PCI P2PDMA support



On 2021-03-12 7:36 p.m., Ira Weiny wrote:
> On Thu, Mar 11, 2021 at 04:31:37PM -0700, Logan Gunthorpe wrote:
>  
>> +int dma_pci_p2pdma_supported(struct device *dev)
>    ^^^
>   bool?

Sure.

> 
>> +{
>> +	const struct dma_map_ops *ops = get_dma_ops(dev);
>> +
>> +	return !ops || ops->flags & DMA_F_PCI_P2PDMA_SUPPORTED;
> 
> Is this logic correct?  I would have expected.
> 
> 	return (ops && ops->flags & DMA_F_PCI_P2PDMA_SUPPORTED);


If ops is NULL then the operations in kernel/dma/direct.c are used and
support is added to those in patch 6. So it is correct as written.

Logan