Date:	Mon, 12 Jan 2015 09:11:17 +0100
From:	Johannes Schauer <j.schauer@...il.de>
To:	wei_wang@...lsil.com.cn, phihag@...hag.de, ben@...adent.org.uk
Cc:	757733@...s.debian.org, linux-kernel@...r.kernel.org
Subject: Re: Bug#757733: RTS2557 SD card reader does not work

Hi,

On Sun, 11 Jan 2015 01:09:19 +0100 Johannes Schauer <j.schauer@...il.de> wrote:
> Weirdly, my SD card reader used to work (but presented the SD card as
> /dev/mmcblk0pX). I do not know why it stopped working though as I didn't reboot
> my laptop for several months. Running an older kernel version (3.14 for
> example) does not fix the problem. Maybe it is related to other parts of my
> (Debian testing) OS. I'll see if I can find a Debian unstable snapshot that
> restores the behaviour I observed last year and try to bisect to find the
> source of the regression.

I spent the past two days trying to reproduce the problem and I'm unable to get
reliable results. Let me explain what I did.

 - December 20 I took a snapshot of my system (but without rebooting) at this
   time my T440s SD card reader worked fine and showed up as /dev/mmcblk0*
 - January 10 (three weeks later) I did a big `apt-get upgrade/dist-upgrade` to
   update all the packages to their Jessie or Sid versions, respectively and
   rebooted. The card reader didn't show up anymore. Nothing on dmesg when I
   inserted my sdcard which would before show me the new registered partitions
 - I put a Debian Sid debootstrap from January 1 2014 on a USB stick and booted
   that. Same thing, no SD card.
 - I put a Debian Sid debootstrap from January 1 2013 on a USB stick and booted
   that. Same thing, no SD card.
 - In the hopes that at least the snapshot from December 20 would work and
   somehow allow me to find out which package upgrade broke my system, I put
   this back on my harddisk and booted it. The SD card reader worked and was
   available as /dev/mmcblk0*
 - I upgraded step by step important packages like linux-image-amd64,
   initramfs, udev, while rebooting after every step. The system kept working.
 - I added /usr /bin /sbin /var /etc /boot and /lib to a git on my / so that I
   would always be able to quickly roll back everything and did `apt-get
   upgrade/dist-upgrade` for the rest of my system and rebooted. Everything
   kept working
 - So at this point I executed the same upgrade path which before made a system
   that was working not working but in this case the SD card reader kept
   working. I had no explanation as I didn't do anything different.
 - I put the prior non-working snapshot of my system from January 10 back which
   had all the upgrades already done. And surprise: this time it worked! The
   exact same hard disk image which before leads to my MMC card reader not
   showing up worked fine this time.
 - I installed Debian Jessie (with the daily installer from [1]) on a USB stick
   and booted that. My card reader keeps working
 - I put put a Debian Sid debootstrap from January 1 2014 on a USB stick and
   booted that (this wasn't working before, see above). This time it worked and
   I was able to mount my SD card.

What do you make from this?

Apparently there are situations where, with the exact same root file system (My
January 20 full snapshot and the January 1 2014 Debian Sid debootstrap) it at
some point did not work but then worked again.

How can this happen?

What else can I try?

Right now everything works and I'm not able to make it not-working again.
Thoughts?

cheers, josch

[1] http://cdimage.debian.org/cdimage/daily-builds/daily/arch-latest/amd64/iso-cd/debian-testing-amd64-netinst.iso

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