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. 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, 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. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
