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

[冯锐]

> 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.

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.