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

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Message-ID: <20190213120358.GA3559@esprimo>
Date:   Wed, 13 Feb 2019 21:03:58 +0900
From:   Takao Indoh <indou.takao@...itsu.com>
To:     Christoph Hellwig <hch@....de>
CC:     Keith Busch <keith.busch@...el.com>,
        Takao Indoh <indou.takao@...fujitsu.com>, <axboe@...com>,
        <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 05:13:47PM +0100, Christoph Hellwig wrote:
> 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.

Ok, let me think about how I should change this patch.
I'm thinking that the problem of this patch is adding processor specific
code into NVMe common driver, is this correct? Or another problem? It
would be great if you could give me a hint to improve this patch.

Thanks,
Takao Indoh