linux-kernel - Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma

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Date: Sun, 5 May 2024 16:23:14 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Zhu Yanjun <zyjzyj2000@...il.com>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Chaitanya Kulkarni <chaitanyak@...dia.com>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Jonathan Corbet <corbet@....net>, Jens Axboe <axboe@...nel.dk>,
	Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	kvm@...r.kernel.org, linux-mm@...ck.org,
	Bart Van Assche <bvanassche@....org>,
	Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
	Amir Goldstein <amir73il@...il.com>,
	"josef@...icpanda.com" <josef@...icpanda.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"daniel@...earbox.net" <daniel@...earbox.net>,
	Dan Williams <dan.j.williams@...el.com>,
	"jack@...e.com" <jack@...e.com>
Subject: Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma_map() for NVMe SGL

On Fri, May 03, 2024 at 04:41:21PM +0200, Zhu Yanjun wrote:
> On 05.03.24 12:18, Leon Romanovsky wrote:
> > From: Chaitanya Kulkarni <kch@...dia.com>

<...>

> > This is an RFC to demonstrate the newly added DMA APIs can be used to
> > map/unmap bvecs without the use of sg list, hence I've modified the pci
> > code to only handle SGLs for now. Once we have some agreement on the
> > structure of new DMA API I'll add support for PRPs along with all the
> > optimization that I've removed from the code for this RFC for NVMe SGLs
> > and PRPs.
> > 

<...>

> > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > index e6267a6aa380..140939228409 100644
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -236,7 +236,9 @@ struct nvme_iod {
> >   	unsigned int dma_len;	/* length of single DMA segment mapping */
> >   	dma_addr_t first_dma;
> >   	dma_addr_t meta_dma;
> > -	struct sg_table sgt;
> > +	struct dma_iova_attrs iova;
> > +	dma_addr_t dma_link_address[128];
> 
> Why the length of this array is 128? Can we increase this length of the
> array?

It is combination of two things:
 * Good enough value for this nvme RFC to pass simple test, which Chaitanya did.
 * Output of various NVME_CTRL_* defines

Thanks