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Date:   Fri, 24 Jul 2020 15:44:37 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Ulf Hansson <ulf.hansson@linaro.org>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Rui Feng <rui_feng@realsil.com.cn>,
        linux-nvme@lists.infradead.org,
        linux-pci <linux-pci@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] mmc: core: Initial support for SD express card/host
Message-ID: <20200724134437.GB3152@lst.de>
References: <20200716141534.30241-1-ulf.hansson@linaro.org> <CAK8P3a1+rwY5uFpUMijgET_W78Tj+tqqKDevgqstjUmmhxdKuA@mail.gmail.com> <CAPDyKFp3D8xZCSGNMm2ZOpa5f5wMwderCuAA5yLMXdjoKFoxQw@mail.gmail.com> <CAK8P3a3wLPv58uqTqyXk7+0Cxoe4vdfahzCxXOp2pdGZDkeFsw@mail.gmail.com>
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On Fri, Jul 24, 2020 at 03:35:47PM +0200, Arnd Bergmann wrote:
> Starting simple is generally a good idea, yes.
> 
> It would be good to have feedback from the nvme driver maintainers.
> 
> One way I can see the handshake working would be to have
> an sdexpress class_driver that provides interfaces for both mmc
> and nvme to link against. The mmc core can then create a
> class device when it finds an sd-express device and that
> class device contains a simple state machine that keeps track of
> what either side think is going on, possibly also providing
> a way to perform callbacks between the two sides.

None of this is in scope for the NVMe spec, so I don't really want
to deal with it in the NVMe driver in any way.  Given that a SD
express card just turns into a normal PCIe link if you really want
to check that something probed I think you'd want to track if any
PCIe driver is bound to the device.  Or just wait and see if we really
need anything after all.