linux-kernel - Re: [PATCH 3/3] mmc: dw_mmc: Add locking to the CTO timer

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Date:   Tue, 3 Oct 2017 11:45:50 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Jaehoon Chung <jh80.chung@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Shawn Lin <shawn.lin@...k-chips.com>
Cc:     Brian Norris <briannorris@...omium.org>,
        Alexandru M Stan <amstan@...omium.org>,
        Ziyuan Xu <xzy.xu@...k-chips.com>,
        Douglas Anderson <dianders@...omium.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH 3/3] mmc: dw_mmc: Add locking to the CTO timer

Hi,

On Wed, Sep 27, 2017 at 1:56 PM, Douglas Anderson <dianders@...omium.org> wrote:
> This attempts to instill a bit of paranoia to the code dealing with
> the CTO timer.  It's believed that this will make the CTO timer more
> robust in the case that we're having very long interrupt latencies.
>
> Note that I originally thought that perhaps this patch was being
> overly paranoid and wasn't really needed, but then while I was running
> mmc_test on an rk3399 board I saw one instance of the message:
>   dwmmc_rockchip fe320000.dwmmc: Unexpected interrupt latency
>
> I had debug prints in the CTO timer code and I found that it was
> running CMD 13 at the time.
>
> ...so even though this patch seems like it might be overly paranoid,
> maybe it really isn't?
>
> Presumably the bad interrupt latency experienced was due to the fact
> that I had serial console enabled as serial console is typically where
> I place blame when I see absurdly large interrupt latencies.  In this
> particular case there was an (unrelated) printout to the serial
> console just before I saw the "Unexpected interrupt latency" printout.
>
> ...and actually, I managed to even reproduce the problems by running
> "iw mlan0 scan > /dev/null" while mmc_test was running.  That not only
> does a bunch of PCIe traffic but it also (on my system) outputs some
> SELinux log spam.
>
> Fixes: 03de19212ea3 ("mmc: dw_mmc: introduce timer for broken command transfer over scheme")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  drivers/mmc/host/dw_mmc.c | 92 +++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 82 insertions(+), 10 deletions(-)

I'm hoping that someone upstream might have some time to test and
review these three patches since I believe that they fix a regression
in 4.14.  I pinged Shawn Lin and found that it's a Chinese holiday
right now so he won't be able to test util next week, but presumably
others might be noticing problems with SD cards or eMMC using dw_mmc
on kernel 4.14, especially with serial console enabled?

Adding linux-rockchip to the CC here.  Original patches can be found
on patchwork.kernel.org...

Thanks!

-Doug