Re: [PATCH 3/3] mmc: rtsx: Add SD Express mode support for RTS5261

[Christoph Hellwig <hch@lst.de>]

On Tue, Oct 27, 2020 at 01:54:46PM +0100, Ulf Hansson wrote:
> > For information security purpose, some companies or business users set their notebook SD as "read only".
> > Because a lot of "read only" requirements from those companies or business users, notebook vendor controls reader write protect pin to achieve it.
> > Notebook BIOS might have option to choose "read only" or not.
> > This is why we think write protect is more important than speed.
> 
> I understand that it may be used, in some way or the other to provide
> a hint to the operating system to mount it in read-only mode.
> 
> Although, if there were a real security feature involved, the internal
> FW of the SD card would also monitor the switch, to support read-only
> mode. As I understand it, that's not the common case.

Yes.  "Security" that relies on the driver to fall back to a different
mode doesn't work.

> 
> > If you prefer to consistent behavior, I can ignore the write protect switch for SD express.
> 
> At this point, I prefer if you would ignore the write protect switch
> in the SD controller driver.

Same here.

> According to Christoph, it should be possible to support read-only
> mode via PCIe/NVMe. You may need to add some tweaks to support this in
> the PCIe controller driver, but I can't advise you how to exactly do
> this.

The NVMe driver already supports write protected namespaces.

I'll ask my contact in the JEDEC SD card working group if there was
any consideration of the read-only handling for classic SD vs NVMe.