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

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Date:   Sun, 4 Mar 2018 16:46:16 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        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

On Thu, 15 Feb 2018 19:22:00 +0100 (CET)
Stefan Wahren <stefan.wahren@...e.com> wrote:

> 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.

It can be included in the ramdisk but somebody would have to add it to
the list of required modules because the dependency is non-obvious.

Thanks

Michal