[PATCH 3/3] mmc: dw_mmc: Add locking to the CTO timer

[Doug Anderson]

Hi,

On Wed, Sep 27, 2017 at 1:56 PM, Douglas Anderson <dianders at chromium.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 at chromium.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