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

[Christoph Hellwig]

On Sun, Apr 26, 2020 at 09:25:46AM +0800, rui_feng@xxxxxxxxxxxxxx wrote:
> From: Rui Feng <rui_feng@xxxxxxxxxxxxxx>
> 
> 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.