linux-kernel - Re: [PATCH 2/2] mmc: bcm2835: print some informational messages during reset

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Date:   Thu, 15 Feb 2018 19:22:00 +0100 (CET)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Michal Suchánek <msuchanek@...e.de>
Cc:     Scott Branden <sbranden@...adcom.com>,
        linux-rpi-kernel@...ts.infradead.org,
        Eric Anholt <eric@...olt.net>,
        bcm-kernel-feedback-list@...adcom.com,
        Gerd Hoffmann <kraxel@...hat.com>, linux-mmc@...r.kernel.org,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-kernel@...r.kernel.org, Ray Jui <rjui@...adcom.com>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] mmc: bcm2835: print some informational messages
 during reset

Hi Michal,

> Michal Suchánek <msuchanek@...e.de> hat am 14. Februar 2018 um 20:47 geschrieben:
> 
> 
> On Wed, 14 Feb 2018 08:50:16 -0800
> Florian Fainelli <f.fainelli@...il.com> wrote:
> 
> > On February 14, 2018 6:38:58 AM PST, Michal Suchanek
> > <msuchanek@...e.de> wrote:
> > >The previous patch does reset during hardware error so make the reset
> > >progress more visible.  
> > 
> > Based on your previous email it looks like this can happen quite
> > frequently so we might be spamming the kernel log with such reset
> > messages. Turning this into a debug print would not be great either,
> > how about a custom sysfs attribute counting the number of times a
> > reset was done?
> 
> Since every such message happens when the system stalls for like half a
> minute I don't think there will be that many until somebody notices
> something is amiss. It might be also helpful in diagnosing if other
> cards lock up in different way - for me the DMA shutdown is short so I
> guess it's the mmc host that is locked up and the DMA engine is fine.
> It might look differently on different systems, though.

FWIW according to your dmesg your RPi doesn't use the DMA engine:

[ 5.004609] sdhost-bcm2835 3f202000.sdhost: unable to initialise DMA channel. Falling back to PIO
[ 5.154518] sdhost-bcm2835 3f202000.sdhost: loaded - DMA disabled

For me it's a chicken and egg problem if the DMA driver is build as a kernel module.

Stefan

> 
> I understand that adding messages it somewhat controversial so I added
> them in separate patch.
> 
> Thanks
> 
> Michal