Re: [PATCH] mmc: dw_mmc: Wait for data transfer after response errors

[Shawn Lin]

å 2016/3/31 1:26, Russell King - ARM Linux åé:
> On Wed, Mar 30, 2016 at 07:16:18PM +0200, Enric Balletbo Serra wrote:
> > 2016-03-24 17:22 GMT+01:00 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>:
> > > On Thu, Mar 24, 2016 at 09:06:45AM -0700, Doug Anderson wrote:
> > > > Russell,
> > > ...
> > > > Presumably this is similar to what you saw: the host saw the CRC error
> > > > but the card knew nothing about it.  Sending the stop command during
> > > > this time confused the card.  Presumably the card was in transfer
> > > > state during this time?
> > >
> > > If the card was in transfer state for a command which expects a stop
> > > command, and that stop command was issued after the card entered
> > > the transfer state, then I'd expect the card to handle it... though
> > > there's always the firmware bug issue.
> > >
> > > If the card hadn't entered transfer state at the time the stop command
> > > was issued.. I think that's more likely to hit card firmware issues.
> > >
> > > With the tuning commands, there's another case you can hit though:
> > > the data transfer may have completed before you get around to sending
> > > the stop command.
> > >
> > > That's why, for sdhci, I came to the conclusion that waiting for the
> > > data transfer to complete or timeout was the best solution for SDHCI.
> >
> > In fact I only saw the problem with dw_mmc-exynos, on dw_mmc-rockchip
> > it doesn't happen because it enables the DW_MCI_QUIRK_BROKEN_DTO
> > behaviour. What does this is use a kernel timer to signal when DTO
> > interrupt does NOT come. Note that if I disable this quirk I can also
> > saw the problem on rockchip.
> >
> > > Maybe, if sending a STOP command does cause card firmware issues, then:
> > >
> > > 1) it provides evidence that trying to send a stop command on response
> > >     CRC error is the wrong thing to do (it was talked about making SDHCI
> > >     do this.)
> >
> > Seems the same here, so guess is the wrong thing to do.
> >
> > > 2) it suggests that the solution I came up with for SDHCI is the better
> > >     solution, rather than trying to immediately recover the situation by
> > >     sending a STOP command.
> >
> > I'm wondering if just enable this quirk on exynos too is the proper
> > solution. Unfortunately I don't have enough documentation to check
> > differences between those controllers.
> > Also will really help have access to some hardware that uses
> > dw_mmc-pltfm to check if, like on exynos, same issue is triggered.
> > Anyone with the hardware who can do some tests?
>
> I'd really suggest that the dw-mmc folk place a moritorium on quirk
> flags, and instead deal with situations like this without resorting
> to this kind of thing.

Some quirks and some callbacks have been cleaned in Jaehoon's repo,and
still some are going to removed. Finally we do plan to turn dw_mmc core
into a pure library..

> sdhci is a good example why the quirk flag approach is totally wrong,
> and shows that it leads to an unmaintainable mess.  If dw-mmc people
> don't want the driver to decend into the same state that sdhci is,
> then things like this should not be quirks.  sdhci already has a
> long-term moritorium on quirk flags until the resulting mess has been
> cleaned up.
>
> The danger that quirk flags cause is also highlighted in your mail:
> it's very likely that this _isn't_ a host controller issue at all,

Two issues found by dw_mmc-rockchip part,
(1) need reset idma when switching between fifo-transfer and
idma-transfer. When biu:ciu > 1:6, idma internal fsm take a risk of
a race condition to maintain its fifo lookup pointer. It can be very
easy reproduce by seting biu:ciu > 1:6.. Common bug for dw_mmc! But 
unfortunately these details was missing in the commit msg.

(2) Missing DTO/DRTO; I missed the thread for this topic, so I need to
reproduce it by setting a simple C model code. I can't say more
currently until we can find a way to easily reproduce it. But I guess
it's NOT a host issue....since I slightly glance at the TMOUT reg at 
dw_mmc databook and find a software timer requirement:

31:8 data_timeout 0xffffff
Value for card Data Read Timeout; same value also used for Data
Starvation by Host timeout. The timeout counter is started only after 
thecard clock is stopped. Value is in number of card output clocks â 
cclk_out of selected card.

Note: The software timer should be used if the timeout value is in the 
order of 100 ms. In this case, read data timeout interrupt needs to be 
disabled.

> but a MMC protocol issue or a card issue - and the behaviour required
> here is not specific to any particular host controller.  The problem
> with having a quirk flag for it is that you end up with some hosts
> enabling it, and other hosts having it disabled only because they
> haven't yet tripped over the issue.


--
Best Regards
Shawn Lin