On 10 October 2017 at 15:31, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > 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. No I can't, but I don't see why that matters. My point is, if we want to go down that road by avoiding the CMD13 polling, that needs to be a separate change, which we can test and confirm on its own. > >> >>> >>> 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. This is already proven, because this how the existing mmc async request mechanism works. In ->post_req() callbacks, host drivers may do dma_unmap_sg(), which is something that could be costly and therefore it's better to start a new request before, such these things can go on in parallel. Kind regards Uffe
