On 28/04/16 14:46, Ulf Hansson wrote: > On 28 April 2016 at 13:02, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >> On 28/04/16 13:34, Ulf Hansson wrote: >>> On 21 April 2016 at 15:28, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>>> The RPMB partition only allows certain commands. In particular, >>>> the tuning command (CMD21) is not allowed - refer JEDEC eMMC >>>> standard v5.1 section 6.2.2 Command restrictions. >>>> >>>> To avoid tuning for RPMB, switch to High Speed mode from HS200 >>>> or HS400 mode if re-tuning has been enabled. And switch back >>>> when leaving RPMB. >>> >>> I would rather just disable re-tuning during this period, instead of >>> changing the speed mode. >>> The primary reason to why, is because the latency it would introduce >>> to first switch to HS speed then back to HS200/400. >> >> I wouldn't expect RPMB accesses to be frequent enough for the latency to matter. >> >>> >>> My concern is not the throughput as I expect read/writes request to an >>> RPMB partition is rather small. >>> >>> Of course I realize that we need to take care when disable re-tuning. >>> Perhaps we can solve that by a re-try mechanism if the RPMB request >>> fails, and thus perform the re-tuning as part of the re-try? >> >> The interdependent nature of RPMB commands suggests that re-trying is not >> possible. It seems to me that you would have to make up a new set of >> commands and start again. i.e. return an error to the user so that they can >> start again. > > Ok. > > So perhaps returning -EAGAIN could work!? I don't think existing code would expect that. Doesn't seem like level of service I would expect from the kernel. And the concern is, that being an error path, it gets overlooked. > >> >> Another dependency is that we always need to re-tune after host runtime >> suspend, which is why we always hit this problem when RPMB is accessed. So > > Just to make sure I understand correctly; I would imagine you hit the > problem *only* when the RPMB partition was already selected, right? Yes > > Because that would then skip the switch command, and you will > therefore try to re-tune after the partition has already been switched > to? Yes > >> to avoid errors you would either need to disable runtime PM when the RPMB >> partition is selected (which might be a long time if we don't get an access >> to another partition), or always switch back to the main partition (not sure >> if that would mess up the RPMB command sequence though). > > I wouldn't mind that we switch back to the main partition when we have > served an RPMB IOCTL request. Of course not in between every mmc > request, in case of using the MULTI IOCTL. > > That would prevent the next regular mmc request on the main partition > to not have to switch partition and thus get decreased latency. Doesn't stop us getting CRC errors because the eMMC needs tuning while in the RPMB partition though. -- 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
