On 10/10/17 16:08, Ulf Hansson wrote: > [...] > >>>>> >>>>> I have also run some test on my ux500 board and enabling the blkmq >>>>> path via the new MMC Kconfig option. My idea was to run some iozone >>>>> comparisons between the legacy path and the new blkmq path, but I just >>>>> couldn't get to that point because of the following errors. >>>>> >>>>> I am using a Kingston 4GB SDHC card, which is detected and mounted >>>>> nicely. However, when I decide to do some writes to the card I get the >>>>> following errors. >>>>> >>>>> root@ME:/mnt/sdcard dd if=/dev/zero of=testfile bs=8192 count=5000 conv=fsync >>>>> [ 463.714294] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 464.722656] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 466.081481] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 467.111236] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 468.669647] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 469.685699] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 471.043334] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 472.052337] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 473.342651] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 474.323760] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 475.544769] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 476.539031] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 477.748474] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> [ 478.724182] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>>>> >>>>> I haven't yet got the point of investigating this any further, and >>>>> unfortunate I have a busy schedule with traveling next week. I will do >>>>> my best to look into this as soon as I can. >>>>> >>>>> Perhaps you have some ideas? >>>> >>>> The behaviour depends on whether you have MMC_CAP_WAIT_WHILE_BUSY. Try >>>> changing that and see if it makes a difference. >>> >>> Yes, it does! I disabled MMC_CAP_WAIT_WHILE_BUSY (and its >>> corresponding code in mmci.c) and the errors goes away. >>> >>> When I use MMC_CAP_WAIT_WHILE_BUSY I get these problems: >>> >>> [ 223.820983] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 224.815795] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 226.034881] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 227.112884] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 227.220275] mmc0: Card stuck in wrong state! mmcblk0 mmc_blk_card_stuck >>> [ 228.686798] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 229.892150] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 231.031890] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> [ 232.239013] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer! >>> 5000+0 records in >>> 5000+0 records out >>> root@ME:/mnt/sdcard >>> >>> I looked at the new blkmq code from patch v10 13/15. It seems like the >>> MMC_CAP_WAIT_WHILE_BUSY is used to determine whether the async request >>> mechanism should be used or not. Perhaps I didn't looked close enough, >>> but maybe you could elaborate on why this seems to be the case!? >> >> MMC_CAP_WAIT_WHILE_BUSY is necessary because it means that a data transfer >> request has finished when the host controller calls mmc_request_done(). i.e. >> polling the card is not necessary. > > Well, that is a rather big change on its own. Earlier we polled with > CMD13 to verify that the card has moved back to the transfer state, in > case it was a write. And that was no matter of MMC_CAP_WAIT_WHILE_BUSY > was set or not. Right!? Yes > > I am not sure it's a good idea to bypass that validation, it seems > fragile to rely only on the busy detection on DAT line for writes. Can you cite something from the specifications that backs that up, because I couldn't find anything to suggest that CMD13 polling was expected. > >> >> Have you tried V9 or V10. There was a fix in V9 related to calling >> ->post_req() which could mess up DMA. > > I have used V10. > >> >> The other thing that could go wrong with DMA is if it cannot accept >> ->post_req() being called from mmc_request_done(). > > I don't think mmci has a problem with that, however why do you want to > do this? Wouldn't that defeat some of the benefits with the async > request mechanism? Perhaps - but it would need to be tested. If there are more requests waiting, one optimization could be to defer ->post_req() until after the next request is started.
