linux-kernel - Re: [PATCH v3 01/20] lib/scatterlist: add flag for indicating P2PDMA segments in an SGL

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Date:   Thu, 30 Sep 2021 04:47:50 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
CC:     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>,
        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>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>
Subject: Re: [PATCH v3 01/20] lib/scatterlist: add flag for indicating P2PDMA
 segments in an SGL

Logan,

> +/*
> + * bit 2 is the third free bit in the page_link on 64bit systems which
> + * is used by dma_unmap_sg() to determine if the dma_address is a PCI
> + * bus address when doing P2PDMA.
> + * Note: CONFIG_PCI_P2PDMA depends on CONFIG_64BIT because of this.
> + */
> +
> +#ifdef CONFIG_PCI_P2PDMA
> +#define SG_DMA_PCI_P2PDMA      0x04UL
> +#else
> +#define SG_DMA_PCI_P2PDMA      0x00UL
> +#endif
> +
> +#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END | SG_DMA_PCI_P2PDMA)
> +

You are doing two things in one patch :-
1. Introducing a new macro to replace the current macros.
2. Adding a new member to those macros.

shouldn't this be split into two patches where you introduce a
macro SG_PAGE_LINK_MASK (SG_CHAIN | SG_END) in prep patch and
update the SF_PAGE_LINK_MASK with SG_DMA_PCI_P2PDMA with related
code?

OR

Is there a reason why it is not split ?

-ck