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Date:   Fri, 23 Oct 2020 11:14:08 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     =?utf-8?B?5Yav6ZSQ?= <rui_feng@realsil.com.cn>,
        Christoph Hellwig <hch@lst.de>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>
Subject: Re: [PATCH 3/3] mmc: rtsx: Add SD Express mode support for RTS5261
Message-ID: <20201023091408.GA5201@lst.de>
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On Fri, Oct 23, 2020 at 10:02:15AM +0200, Ulf Hansson wrote:
> > > Is there no mechanism to support read-only PCIe/NVMe based storage devices?
> > > If that is the case, maybe it's simply better to not support the readonly option
> > > at all for SD express cards?
> > >
> > I think there's no mechanism to support read-only PCIe/NVMe based storage devices.
> 
> I have looped in Christoph, maybe he can give us his opinion on this.

NVMe namespaces can have a bunch of 'write protection' modes advertised
by the controller, which Linux respects.  The controller in this case would
be part of the SD-Card.  IMHO it is a quality of implementation issue
of the SD-Card/Controller to have the the write protection mode of the
namespace(s) match that of the SD interface, and the SD card spec should
talk about that if it doesn't already.