On 13/01/12 15:14, Ulf Hansson wrote: >>>>> In principles this means the following sequence: >>>>> >>>>> We will rely on that the get_cd function will return 0 (indicating card is >>>>> removed) when the card is "slowly" removed at the point when the rescan >>>>> function is calling it through the bus_ops->detect --> >>>>> _mmc_detect_card_removed function. >>>>> >>>>> This then becomes a race, meaning that the rescan function must be >>>>> executing >>>>> at the same time the get_cd function will returns 0. Otherwise the rescan >>>>> function will not remove the card. >>>>> >>>>> Thus my conclusion is that "[PATCH 2/4 v4] MMC/SD: Add callback >>>>> function to >>>>> detect card" will likely improve behavior but is not the safe solution to >>>>> handle "slowly" removed cards. >>>>> >>>>> Again, to be sure, we must let the mmc_detect_card_remove function >>>>> trigger a >>>>> rescan when _mmc_detect_card_removed has detected that the card is >>>>> removed. >>>>> This should be safe in all circumstances. >>>> sdhci has no problem because it does this: >>>> >>>> - the host controller debounces the card detect line >>>> - the host controller records whether or not the card is present >>>> - the sdhci driver prevents (errors out) requests when the card is >>>> not present >>> Debouncing will just be a way of triggering the problem more seldom. Or in >>> worst case, state the card has been removed even if it has not. >> >> If a delay is used with mmc_detect_change, debouncing is not necessary. >> >>> Just because you get a GPIO irq on the detect line does not mean the card is >>> removed, debouncing or not. I consider this as pure mechanical switch which >>> likely has glitches and I don't see that we should trust it fully. We only >>> want to trigger a detect work, which is exactly what is done in the patch >>> from Guennadi Liakhovetski "mmc: add a generic GPIO card-detect helper". >> >> The original problem was "slow card removal". "Unreliable card detect" >> is a separate problem. Currently there is polling (MMC_CAP_NEEDS_POLL) >> for that. Alternatively there is MMC_CAP2_RESCAN_ON_ERROR as we have >> discussed. > > I do not understand why you mention "Unreliable card detect"? That has > nothing to do with this patch. > > So to conclude the discussion, do you believe that this patch is acceptable > as long as we add a CAPS2 option "MMC_CAP2_RESCAN_ON_ERROR", which if not > set will prevent the detect work from being scheduled from > mmc_detect_card_removed? Yes > >> >>> If each host driver that supports GPIO card detect makes use of the >>> card-detect helper and if we accept a version of this patch, I think the >>> situation should be safe in all cases. Moreover GPIO debouncing will never >>> be needed for GPIO card detect for your sdhci driver either. >> >> Safe in all cases, except at least the 3 already given: >> - card is buggy and sometimes fails several commands in a row > I doubt this will become a real problem. If a card fails several times in a > row, upper FS layers wont be happy either. So likely we are screwed anyway. > Don't you think? >> - upper layers want to attempt to recover an unresponsive card > This is not implemented as of right now. I see no problem that my patch will > prevent this from being implemented in the future. >> - even in the case of slow removal, the vendor wants the card >> to show as removed immediately whether or not there is any I/O > That is correct and can not be fully solved unless you use > MMC_CAP_NEEDS_POLL. I doubt that one would like to use polling in favor of > card detect only to take care of this issue though. So I believe it is more > likely you want to trigger a card removal when receiving I/O. Kind of > "Better late than never". :-) > > > By the way, thanks for keeping up the frequency in this quite long discussion. > > BR > Ulf Hansson > -- 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
