From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751763AbdFHR0t (ORCPT ); Thu, 8 Jun 2017 13:26:49 -0400 Received: from conssluserg-02.nifty.com ([210.131.2.81]:22478 "EHLO conssluserg-02.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751734AbdFHR0r (ORCPT ); Thu, 8 Jun 2017 13:26:47 -0400 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-02.nifty.com v58HQaLc028480 X-Nifty-SrcIP: [209.85.161.175] MIME-Version: 1.0 In-Reply-To: <20170608174311.4f012cc5@bbrezillon> References: <1496836352-8016-1-git-send-email-yamada.masahiro@socionext.com> <1496836352-8016-11-git-send-email-yamada.masahiro@socionext.com> <20170607155701.4bc89ad8@bbrezillon> <20170608091239.0095511b@bbrezillon> <20170608132620.17fc7c96@bbrezillon> <20170608174311.4f012cc5@bbrezillon> From: Masahiro Yamada Date: Fri, 9 Jun 2017 02:26:34 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 10/23] mtd: nand: denali: rework interrupt handling To: Boris Brezillon Cc: Marek Vasut , Richard Weinberger , Cyrille Pitchen , Artem Bityutskiy , Linux Kernel Mailing List , Dinh Nguyen , linux-mtd@lists.infradead.org, Masami Hiramatsu , Chuanxiao Dong , Jassi Brar , Brian Norris , Enrico Jorns , David Woodhouse Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v58HR4iN021531 Hi Boris 2017-06-09 0:43 GMT+09:00 Boris Brezillon : > On Thu, 8 Jun 2017 21:58:00 +0900 > Masahiro Yamada wrote: > >> Hi Boris, >> >> 2017-06-08 20:26 GMT+09:00 Boris Brezillon : >> > On Thu, 8 Jun 2017 19:41:39 +0900 >> > Masahiro Yamada wrote: >> > >> >> Hi Boris, >> >> >> >> >> >> 2017-06-08 16:12 GMT+09:00 Boris Brezillon : >> >> > Le Thu, 8 Jun 2017 15:10:18 +0900, >> >> > Masahiro Yamada a écrit : >> >> > >> >> >> Hi Boris, >> >> >> >> >> >> >> >> >> 2017-06-07 22:57 GMT+09:00 Boris Brezillon : >> >> >> > On Wed, 7 Jun 2017 20:52:19 +0900 >> >> >> > Masahiro Yamada wrote: >> >> >> > >> >> >> > >> >> >> >> -/* >> >> >> >> - * This is the interrupt service routine. It handles all interrupts >> >> >> >> - * sent to this device. Note that on CE4100, this is a shared interrupt. >> >> >> >> - */ >> >> >> >> -static irqreturn_t denali_isr(int irq, void *dev_id) >> >> >> >> +static uint32_t denali_wait_for_irq(struct denali_nand_info *denali, >> >> >> >> + uint32_t irq_mask) >> >> >> >> { >> >> >> >> - struct denali_nand_info *denali = dev_id; >> >> >> >> + unsigned long time_left, flags; >> >> >> >> uint32_t irq_status; >> >> >> >> - irqreturn_t result = IRQ_NONE; >> >> >> >> >> >> >> >> - spin_lock(&denali->irq_lock); >> >> >> >> + spin_lock_irqsave(&denali->irq_lock, flags); >> >> >> >> >> >> >> >> - /* check to see if a valid NAND chip has been selected. */ >> >> >> >> - if (is_flash_bank_valid(denali->flash_bank)) { >> >> >> >> - /* >> >> >> >> - * check to see if controller generated the interrupt, >> >> >> >> - * since this is a shared interrupt >> >> >> >> - */ >> >> >> >> - irq_status = denali_irq_detected(denali); >> >> >> >> - if (irq_status != 0) { >> >> >> >> - /* handle interrupt */ >> >> >> >> - /* first acknowledge it */ >> >> >> >> - clear_interrupt(denali, irq_status); >> >> >> >> - /* >> >> >> >> - * store the status in the device context for someone >> >> >> >> - * to read >> >> >> >> - */ >> >> >> >> - denali->irq_status |= irq_status; >> >> >> >> - /* notify anyone who cares that it happened */ >> >> >> >> - complete(&denali->complete); >> >> >> >> - /* tell the OS that we've handled this */ >> >> >> >> - result = IRQ_HANDLED; >> >> >> >> - } >> >> >> >> + irq_status = denali->irq_status; >> >> >> >> + >> >> >> >> + if (irq_mask & irq_status) { >> >> >> >> + spin_unlock_irqrestore(&denali->irq_lock, flags); >> >> >> >> + return irq_status; >> >> >> >> } >> >> >> >> - spin_unlock(&denali->irq_lock); >> >> >> >> - return result; >> >> >> >> + >> >> >> >> + denali->irq_mask = irq_mask; >> >> >> >> + reinit_completion(&denali->complete); >> >> >> > >> >> >> > These 2 instructions should be done before calling >> >> >> > denali_wait_for_irq() (for example in denali_reset_irq()), otherwise >> >> >> > you might loose events if they happen between your irq_status read and >> >> >> > the reinit_completion() call. >> >> >> >> >> >> No. >> >> >> >> >> >> denali->irq_lock avoids a race between denali_isr() and >> >> >> denali_wait_for_irq(). >> >> >> >> >> >> >> >> >> The line >> >> >> denali->irq_status |= irq_status; >> >> >> in denali_isr() accumulates all events that have happened >> >> >> since denali_reset_irq(). >> >> >> >> >> >> If the interested IRQs have already happened >> >> >> before denali_wait_for_irq(), it just return immediately >> >> >> without using completion. >> >> >> >> >> >> I do not mind adding a comment like below >> >> >> if you think my intention is unclear, though. >> >> >> >> >> >> /* Return immediately if interested IRQs have already happend. */ >> >> >> if (irq_mask & irq_status) { >> >> >> spin_unlock_irqrestore(&denali->irq_lock, flags); >> >> >> return irq_status; >> >> >> } >> >> >> >> >> >> >> >> > >> >> > My bad, I didn't notice you were releasing the lock after calling >> >> > reinit_completion(). I still find this solution more complex than my >> >> > proposal, but I don't care that much. >> >> >> >> >> >> At first, I implemented exactly like you suggested; >> >> denali->irq_mask = irq_mask; >> >> reinit_completion(&denali->complete) >> >> in denali_reset_irq(). >> >> >> >> >> >> IIRC, things were like this. >> >> >> >> Some time later, you memtioned to use ->cmd_ctrl >> >> instead of ->cmdfunc. >> >> >> >> Then I had a problem when I needed to implement >> >> denali_check_irq() in >> >> http://patchwork.ozlabs.org/patch/772395/ >> >> >> >> denali_wait_for_irq() is blocked until interested IRQ happens. >> >> but ->dev_ready() hook should not be blocked. >> >> It should return if R/B# transition has happened or not. >> > >> > Nope, it should return whether the NAND is ready or not, not whether a >> > busy -> ready transition occurred or not. It's typically done by >> > reading the NAND STATUS register or by checking the R/B pin status. >> >> Checking the R/B pin is probably impossible unless >> the pin is changed into a GPIO port. >> >> I also considered NAND_CMD_STATUS, but >> I can not recall why I chose the current approach. >> Perhaps I thought returning detected IRQ >> is faster than accessing the chip for NAND_CMD_STATUS. >> >> I can try NAND_CMD_STATUS approach if you like. > > Depends what you're trying to do. IIUC, you use denali_wait_for_irq() > inside your ->reset()/->read/write_{page,oob}[_raw]() methods, which is > perfectly fine (assuming CUSTOM_PAGE_ACCESS is set) since these hooks > are expected to wait for chip readiness before returning. > > You could also implement ->waitfunc() using denali_wait_for_irq() if > you're able to detect R/B transitions, R/B transition will set INTR__INT_ACT interrupt. I think it is easy in my implementation of denali_wait_for_irq(), like denali_wait_for_irq(denali, INTR__INT_ACT); But, you are suggesting me to change it. In your way, you give IRQ masks to denali_reset_irq(), like denali_reset_irq(denali, INTR__ERASE_COMP | INTR__ERASE_FAIL); Then, we have no room of IRQ bit in denali_wait_for_irq(). How will you implement it? > but I'm not sure it's worth it, > because you overload almost all the methods using this hook (the only > one remaining is ->onfi_set_features(), and using STATUS polling should > not be an issue in this case). > > Implementing ->dev_ready() is not necessary. When not provided, the > core falls back to STATUS polling and you seem to support > NAND_CMD_STATUS in denali_cmdfunc(). Note that even if it's not fully > reliable in the current driver, you're switching to ->cmd_ctrl() at the > end of the series anyway, so we should be good after that. ->dev_ready() is optional, but we may end up with waiting more than needed. case NAND_CMD_RESET: if (chip->dev_ready) break; udelay(chip->chip_delay); chip->chip_delay is probably set large enough, so this is not optimal. If I add something more, the following two bugs were found by denali_dev_ready(). commit 3158fa0e739615769cc047d2428f30f4c3b6640e commit c5d664aa5a4c4b257a54eb35045031630d105f49 If NAND core is fine, denali_dev_ready() works fine too. If not, it is a sign of bug of nand_command(_lp). This is contributing to the core improvement. >> >> IIRC, I was thinking like this: >> >> One IRQ line may be shared among multiple hardware including Denali. >> denali_pci may do this. >> >> The Denali IRQ handler need to check irq status >> because it should return IRQ_HANDLED if the event comes from Denali controller. >> Otherwise, the event comes from different hardware, so >> Denali IRQ handler should return IRQ_NONE. > > Correct. > >> >> wait_for_completion_timeout() may bail out with timeout error, >> then proceed to denali_reset_irq() for the next operation. > > Before calling denali_reset_irq() you should re-mask the irqs you > unmasked in #1. Actually, calling denali_reset_irq() after > wait_for_completion_timeout() is not even needed here because you'll > clear pending irqs before launching the next NAND command. > >> Afterwards, the event actually may happen, and invoke IRQ handler. > > Not if you masked IRQs after wait_for_completion_timeout() returned. wait_for_completion_timeout(&denali->complete, msecs_to_jiffies(1000)); <<< WHAT IF IRQ EVENT HAPPENS HERE ? >>> iowrite32(0, denali->flash_reg + INTR_EN(denali->flash_bank)); Also, you ignore the return value of wait_for_completion_timeout(), then drop my precious error message() dev_err(denali->dev, "timeout while waiting for irq 0x%x\n", denali->irq_mask) > Here is a patch to show you what I had in mind [1] (it applies on top > of this patch). AFAICT, there's no races, no interrupt loss, and you > get rid of the ->irq_mask/status/lock fields. > > [1]http://code.bulix.org/fufia6-145571 > Problem Scenario A [1] wait_for_completion_timeout() exits with timeout. [2] IRQ happens and denali_isr() is invoked [3] iowrite32(0, denali->flash_reg + INTR_EN(denali->flash_bank)); [4] status = ioread32(denali->flash_reg + INTR_STATUS(bank)) & ioread32(denali->flash_reg + INTR_EN(bank)); (status is set to 0 because INTR_EN(bank) is now 0) [5] return IRQ_NONE; [6] kernel complains "irq *: nobody cared" Problem Scenario B (unlikely to happen, though) [1] wait_for_completion_timeout() exits with timeout. [2] IRQ happens and denali_isr() is invoked [3] iowrite32(0, denali->flash_reg + INTR_EN(denali->flash_bank)); [4] chip->select_chip(mtd, -1) [5] denali->flash_bank = -1 [6] status = ioread32(denali->flash_reg + INTR_STATUS(bank)) & ioread32(denali->flash_reg + INTR_EN(bank)); ( access to non-existing INTR_STATUS(-1) ) -- Best Regards Masahiro Yamada