From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ulf Hansson Subject: Re: [PATCH] mmc: core: Force a "detect" to handle non-properly removed cards Date: Mon, 9 Jan 2012 15:27:55 +0100 Message-ID: <4F0AF96B.4050500@stericsson.com> References: <1325586798-16276-1-git-send-email-ulf.hansson@stericsson.com> <4F04C412.1030604@intel.com> <4F0AC942.4060404@stericsson.com> <4F0AD879.10801@intel.com> <4F0AE82C.10000@stericsson.com> <4F0AF157.7090101@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from eu1sys200aog102.obsmtp.com ([207.126.144.113]:43645 "EHLO eu1sys200aog102.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755147Ab2AIO2T (ORCPT ); Mon, 9 Jan 2012 09:28:19 -0500 In-Reply-To: <4F0AF157.7090101@intel.com> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Adrian Hunter Cc: "linux-mmc@vger.kernel.org" , Chris Ball , Per FORLIN , Johan RUDHOLM , Lee Jones Adrian Hunter wrote: > On 09/01/12 15:14, Ulf Hansson wrote: >>>> My concern is more about what we actually can trust; either the GPIO irq >>>> which likely is giving more than one irq when inserting/removing a card >>>> since the slot is probably not glitch free, or that a "rescan" runs to make >>>> sure a CMD13 is accepted from the previously inserted card. >>> Yes, I guess you would need to debounce the GPIO if you wanted to rely on it. >>> >>>> Moreover, the issue this patch tries to solve can not be solved without >>>> doing a "rescan" which must be triggered from the the block layer some how. >>>> I thought this new function that you previously added >>>> "mmc_detect_card_remove" was the proper place to do this. >>>> >>>>>> Let the mmc_detect_card_removed function trigger a new detect >>>>>> work immediately when it discovers that a card has been removed. >>>>> This is changing some long-standing functionality i.e. the card is not >>>>> removed >>>>> without a card detect event. It is difficult to know whether that will be >>>>> very >>>>> bad for poor quality cards, >>>> Doing a mmc_detect (rescan) will in the end just issue a CMD13 to the card >>>> to make sure it is still present, that is already done from the block layer >>>> after each read/write request. So I can not see that "poor quality cards" >>>> will have any further problem with this patch, but I might miss something!? >>> The block driver has never caused a card to be removed before. That is new >>> and it is designed to preserve existing behaviour i.e. do not remove a card >>> without a card detect event. >> True, but is this a problem!? > > Better not to find out. :-) Then there is lot of other things around mmc we also should not change. > >> Anyway, this is the actual issue this patch is trying to solve. If you >> remove a card "slowly", a "rescan" work, which the GPIO irq has triggered to >> run will run the CMD13 to verify that the card is still there. Since it has >> not completely been removed the CMD13 will succeed and the card will not be >> removed. >> >> Moreover every other new block request will soon start to fail and always >> do; until a new rescan is triggered (which is when you insert a new card or >> do a suspend-resume cycle). In practice I think it is more preferred that >> the card gets removed and it's corresponding block device. > > There are other ways to solve that problem. Apart from my previous > suggestion, there is also the possibility to make use of ->get_cd > instead of CMD13, someone already posted a patch for that > "[PATCH 2/4 v4] MMC/SD: Add callback function to detect card" > but it should probably be selected on a per driver basis (i.e. add a > MMC_CAP2 for it). I guess you would still need to debounce the GPIO > though. > Unfortunately that wont help to solve this issue either. That patch will only prevent you from executing a CMD13 if the get_cd function says the card is still there. I kind of micro optimization I think, unless you very often encounters errors in the block layer. The key in this patch is that a rescan work is triggered to fully verify that the card is still there and if not, it can remove it. I don't think this is such a big matter, but of course this is my own opinion. :-) >>> You are assuming: >>> 1. that a poor quality card will not return errors for a few >>> commands and then resume operation >> I see your point. I did some tests with a bunch of old crappy cards, both SD >> and MMC which I had in my collection. I have found none of these to trigger >> a undesirable removal of the card. >> >> Of course I have only a subset of all cards, so this can not be fully tested >> for all existing cards. >> >>> 2. that removing a card on error is desirable >> Well, we will just fire of a rescan work to check if the card has been >> removed. If it is still there it will of course not be removed. > > Not if it has stopped responding. Again, this is a change in behaviour. > Previously, a card that stopped responding was not removed. > > Perhaps in the future someone will want to try to recover cards that > stop responding, for example by power-cycling. That would be in > conflict with your approach because it would power cycle on every single > card removal. > >>> Both those assumptions may be true, but there is no evidence that they are. >>> >>> >>>>>> This will solve the described issue above. Moreover we make sure >>>>>> the detect work is executed as soon as possible, since there is >>>>>> no reason for waiting for a "delayed" detect to happen. >>>>>> >>>>>> Signed-off-by: Ulf Hansson >>>>>> --- >>>>>> drivers/mmc/core/core.c | 24 +++++++++++++----------- >>>>>> include/linux/mmc/host.h | 1 - >>>>>> 2 files changed, 13 insertions(+), 12 deletions(-) >>>>>> >>>>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c >>>>>> index 4770807..7bc02f4 100644 >>>>>> --- a/drivers/mmc/core/core.c >>>>>> +++ b/drivers/mmc/core/core.c >>>>>> @@ -1462,7 +1462,6 @@ void mmc_detect_change(struct mmc_host *host, >>>>>> unsigned long delay) >>>>>> WARN_ON(host->removed); >>>>>> spin_unlock_irqrestore(&host->lock, flags); >>>>>> #endif >>>>>> - host->detect_change = 1; >>>>>> mmc_schedule_delayed_work(&host->detect, delay); >>>>>> } >>>>>> >>>>>> @@ -2077,18 +2076,23 @@ int _mmc_detect_card_removed(struct mmc_host >>>>>> *host) >>>>>> int mmc_detect_card_removed(struct mmc_host *host) >>>>>> { >>>>>> struct mmc_card *card = host->card; >>>>>> + int ret = 1; >>>>>> >>>>>> WARN_ON(!host->claimed); >>>>>> - /* >>>>>> - * The card will be considered unchanged unless we have been asked to >>>>>> - * detect a change or host requires polling to provide card >>>>>> detection. >>>>>> - */ >>>>>> - if (card&& !host->detect_change&& !(host->caps& >>>>>> MMC_CAP_NEEDS_POLL)) >>>>>> - return mmc_card_removed(card); >>>>>> >>>>>> - host->detect_change = 0; >>>>>> + if (card&& !mmc_card_removed(card)) { >>>>>> + if (_mmc_detect_card_removed(host)) { >>>>>> + /* >>>>>> + * Make sure a detect work is always executed and also >>>>>> + * do it as soon as possible. >>>>>> + */ >>>>>> + cancel_delayed_work(&host->detect); >>>>>> + mmc_detect_change(host, 0); >>>>>> + } >>>>>> + ret = mmc_card_removed(card); >>>>>> + } >>>>>> >>>>>> - return _mmc_detect_card_removed(host); >>>>>> + return ret; >>>>>> } >>>>>> EXPORT_SYMBOL(mmc_detect_card_removed); >>>>>> >>>>>> @@ -2112,8 +2116,6 @@ void mmc_rescan(struct work_struct *work) >>>>>> && !(host->caps& MMC_CAP_NONREMOVABLE)) >>>>>> host->bus_ops->detect(host); >>>>>> >>>>>> - host->detect_change = 0; >>>>>> - >>>>>> /* >>>>>> * Let mmc_bus_put() free the bus/bus_ops if we've found that >>>>>> * the card is no longer present. >>>>>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h >>>>>> index 031d865..09fa5e6 100644 >>>>>> --- a/include/linux/mmc/host.h >>>>>> +++ b/include/linux/mmc/host.h >>>>>> @@ -305,7 +305,6 @@ struct mmc_host { >>>>>> int claim_cnt; /* "claim" nesting count */ >>>>>> >>>>>> struct delayed_work detect; >>>>>> - int detect_change; /* card detect flag */ >>>>>> struct mmc_hotplug hotplug; >>>>>> >>>>>> const struct mmc_bus_ops *bus_ops; /* current bus driver */ >>>> Br >>>> Ulf Hansson >>>> >>> >> > >