linux-kernel - Re: [PATCH] mmc: rtsx: Add SD Express mode support for RTS5261

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Date:   Mon, 27 Apr 2020 13:07:20 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     冯锐 <rui_feng@...lsil.com.cn>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] mmc: rtsx: Add SD Express mode support for RTS5261

On Mon, Apr 27, 2020 at 11:41 AM 冯锐 <rui_feng@...lsil.com.cn> wrote:
>
>
> > On Sun, Apr 26, 2020 at 09:25:46AM +0800, rui_feng@...lsil.com.cn wrote:
> > > From: Rui Feng <rui_feng@...lsil.com.cn>
> > >
> > > RTS5261 support legacy SD mode and SD Express mode.
> > > In SD7.x, SD association introduce SD Express as a new mode.
> > > SD Express mode is distinguished by CMD8.
> > > Therefore, CMD8 has new bit for SD Express.
> > > SD Express is based on PCIe/NVMe.
> > > RTS5261 uses CMD8 to switch to SD Express mode.
> >
> > So how does this bit work?  They way I imagined SD Express to work is that
> > the actual SD Card just shows up as a real PCIe device, similar to say
> > Thunderbolt.
>
> New SD Express card has dual mode. One is SD mode and another is PCIe mode.
> In PCIe mode, it act as a PCIe device and use PCIe protocol not Thunderbolt protocol.

I think what Christoph was asking about is why you need to issue any commands at
all in SD mode when you want to use PCIe mode instead. What happens if you load
the NVMe driver before loading the rts5261 driver?

       Arnd