linux-kernel - Re: [PATCH 1/2] mmc: bcm2835: reset host on timeout

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Date:   Wed, 14 Feb 2018 16:36:49 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Michal Suchanek <msuchanek@...e.de>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Eric Anholt <eric@...olt.net>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        Julia Lawall <Julia.Lawall@...6.fr>, linux-mmc@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mmc: bcm2835: reset host on timeout

On Wed, 14 Feb 2018 15:58:31 +0100
Stefan Wahren <stefan.wahren@...e.com> wrote:

> Hi Michal,
> 
> Am 14.02.2018 um 15:38 schrieb Michal Suchanek:
> > The bcm2835 mmc host tends to lock up for unknown reason so reset
> > it on timeout. The upper mmc block layer tries retransimitting with
> > single blocks which tends to work out after a long wait.
> >
> > This is better than giving up and leaving the machine broken for no
> > obvious reason.  
> 
> could you please provide more information about this issue (affected
> hardware, kernel config, version, dmesg, reproducible scenario)?
> 

The RPi3 is known to not work with some SD cards. You can find some
wiki pages with large tables of known-working and known-broken cards. I
have a couple of RPi3 boards and a card that works and card that does
not. I tried debugging the issue but did not find anything I can do
about it - AFAICT the issue happens somewhere inside the MMC controller
IP. 

I have no inside knowledge of the controller in question but during
testing I tried to reset the controller whenever the issue happens so I
can continue running the test system for a longer time until it gets
unusable. While I did not find any solution to the problem the
workaround with resetting the controller works quite reliably for me.

So I am posting it in the hope that people with the wrong combination
of RPi3 and SD card will not get a blank screen but rather a system
that boots but tends to lock up for half a minute occasionally.

Thanks

Michal