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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Fri, 22 May 2020 12:32:23 +0200
Message-ID: <CAK8P3a3Uk_fmJ3UA1nuChHLC6w3p_wZfkqqRLvB01W0uLEE3-w@mail.gmail.com>
Subject: Re: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Ulf Hansson <ulf.hansson@linaro.org>,
        =?UTF-8?B?5Yav6ZSQ?= <rui_feng@realsil.com.cn>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Fri, May 22, 2020 at 11:16 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, May 19, 2020 at 03:59:23PM +0800, rui_feng@realsil.com.cn wrote:
> > From: rui_feng <rui_feng@realsil.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.
> >
> > Signed-off-by: rui_feng <rui_feng@realsil.com.cn>
> > ---
> > v2: remove config option MISC_RTSX_PCI_SD_EXPRESS
> > ---
> >
> >  drivers/misc/cardreader/rts5261.c  |  5 ++++
> >  drivers/misc/cardreader/rts5261.h  | 23 ----------------
> >  drivers/misc/cardreader/rtsx_pcr.c |  5 ++++
> >  drivers/mmc/core/sd_ops.c          |  9 ++++++-
> >  drivers/mmc/host/rtsx_pci_sdmmc.c  | 43 ++++++++++++++++++++++++++++++
> >  include/linux/mmc/host.h           |  1 +
> >  include/linux/rtsx_pci.h           | 27 +++++++++++++++++++
> >  7 files changed, 89 insertions(+), 24 deletions(-)
>
> If I can get an ack from the MMC maintainer, I can take this in my
> tree...
>
> {hint}

I think this feature needs much more discussion to make sure we
get a good user experience when it gets added to all mmc controllers.

rtsx is a bit of a special case for mmc controllers already, but we will
likely see the same requirements for a lot more mmc host drivers.

I suspect we need to tie in both the mmc block and nvme device
drivers to properly do a handover, to ensure that there is a way to
identify the block device as reliably getting probed as at least one
of the two (sd or nvme) and to get identified as the same device
during the handover, in particular across a suspend or hibernate
event.

I understand that this patch is very desirable for users, but let's
not rush it.

     Arnd