linux-kernel - Re: [PATCH] nvme: Enable acceleration feature of A64FX processor

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Message-ID: <20190205161347.GA847@lst.de>
Date:   Tue, 5 Feb 2019 17:13:47 +0100
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Takao Indoh <indou.takao@...itsu.com>,
        Takao Indoh <indou.takao@...fujitsu.com>, axboe@...com,
        hch@....de, sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: Enable acceleration feature of A64FX processor

On Tue, Feb 05, 2019 at 07:39:06AM -0700, Keith Busch wrote:
> > Standard PCIe devices can use Relaxed Ordering (RO) by setting Attr
> > field in the TLP header, however, this mechanism cannot be utilized if
> > the device does not support RO feature. Fujitsu A64FX processor has an
> > alternate feature to enable RO in its Root Port by setting the bit 56 of
> > DMA address. This mechanism enables to utilize RO feature even if the
> > device does not support standard PCIe RO.
> 
> I think you're better of just purchasing devices that support the
> capability per spec rather than with a non-standard work around.

Agreed, this seems like a pretty gross hack.