From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 10/13] megaraid_sas: set virt_boundary_mask in the scsi
 host
Date: Mon, 17 Jun 2019 10:44:33 +0200
Message-ID: <20190617084433.GA7969@lst.de>
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To: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>, Sebastian Ott <sebott@linux.ibm.com>, Sagi Grimberg <sagi@grimberg.me>, Max Gurtovoy <maxg@mellanox.com>, Bart Van Assche <bvanassche@acm.org>, Ulf Hansson <ulf.hansson@linaro.org>, Alan Stern <stern@rowland.harvard.edu>, Oliver Neukum <oneukum@suse.com>, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, linux-mmc@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, "PDL,MEGARAIDLINUX" <megaraidlinux.pdl@broadcom.com>, PDL-MPT-FUSIONLINUX <mpt-fusionlinux.pdl@broadcom.com>, linux-hyperv@vger.kernel.org, linux-usb@vger.kernel.org, usb-storage@lists.one-eyed-alien.net, linux-kernel@vger.kernel.org
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On Fri, Jun 14, 2019 at 01:28:47AM +0530, Kashyap Desai wrote:
> Is there any changes in API  blk_queue_virt_boundary? I could not find
> relevant code which account for this. Can you help ?
> Which git repo shall I use for testing ? That way I can confirm, I didn't
> miss relevant changes.

Latest mainline plus the series (which is about to get resent).
blk_queue_virt_boundary now forced an unlimited max_hw_sectors as that
is how PRP-like schemes work, to work around a block driver merging
bug.  But we also need to communicate that limit to the DMA layer so
that we don't set a smaller iommu segment size limitation.

> >From your above explanation, it means (after this patch) max segment size
> of the MR controller will be set to 4K.
> Earlier it is possible to receive single SGE of 64K datalength (Since max
> seg size was 64K), but now the same buffer will reach the driver having 16
> SGEs (Each SGE will contain 4K length).

No, there is no more limit for the size of the segment at all,
as for PRPs each PRP is sort of a segment from the hardware perspective.
We just require the segments to not have gaps, as PRPs don't allow for
that.

That being said I think these patches are wrong for the case of megaraid
or mpt having both NVMe and SAS/ATA devices behind a single controller.
Is that a valid configuration?