From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Richard Weinberger <richard@nod.at>,
Marek Vasut <marek.vasut@gmail.com>,
Artem Bityutskiy <artem.bityutskiy@linux.intel.com>,
Chuanxiao Dong <chuanxiao.dong@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Dinh Nguyen <dinguyen@kernel.org>,
linux-mtd@lists.infradead.org,
Masami Hiramatsu <mhiramat@kernel.org>,
Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
Jassi Brar <jaswinder.singh@linaro.org>,
Brian Norris <computersforpeace@gmail.com>,
Enrico Jorns <ejo@pengutronix.de>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v5 10/23] mtd: nand: denali: rework interrupt handling
Date: Thu, 8 Jun 2017 21:58:00 +0900 [thread overview]
Message-ID: <CAK7LNARbaAKyB2ss780o=L=sqqUdz=fix+PaxW_ODDAM63VXOw@mail.gmail.com> (raw)
In-Reply-To: <20170608132620.17fc7c96@bbrezillon>
Hi Boris,
2017-06-08 20:26 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
> On Thu, 8 Jun 2017 19:41:39 +0900
> Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
>
>> Hi Boris,
>>
>>
>> 2017-06-08 16:12 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
>> > Le Thu, 8 Jun 2017 15:10:18 +0900,
>> > Masahiro Yamada <yamada.masahiro@socionext.com> a écrit :
>> >
>> >> Hi Boris,
>> >>
>> >>
>> >> 2017-06-07 22:57 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
>> >> > On Wed, 7 Jun 2017 20:52:19 +0900
>> >> > Masahiro Yamada <yamada.masahiro@socionext.com> 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.
>> So, I accumulate IRQ events in denali->irq_status
>> that have happened since denali_reset_irq().
>
> Yep, I see that.
>
>>
>>
>>
>> >>
>> >>
>> >>
>> >> > You should also clear existing interrupts
>> >> > before launching your operation, otherwise you might wakeup on previous
>> >> > events.
>> >>
>> >>
>> >> I do not see a point in your suggestion.
>> >>
>> >> denali_isr() reads out IRQ_STATUS(i) and immediately clears IRQ bits.
>> >>
>> >> IRQ events triggered by previous events are accumulated in denali->irq_status.
>> >>
>> >> denali_reset_irq() clears it.
>> >>
>> >> denali->irq_status = 0;
>> >
>> > Well, it was just a precaution, in case some interrupts weren't cleared
>> > during the previous test (for example if they were masked before the
>> > event actually happened, which can occur if you have a timeout, but
>> > the event is detected afterward).
>>
>> Turning on/off IRQ mask is problematic.
>> So I did not do that.
>
> I don't see why this is a problem. That's how it usually done.
>
>>
>> I enable IRQ mask in driver probe.
>> I think this approach is more robust when we consider race conditions
>> like you mentioned.
>
> I'd like to hear more about the reasons you think it's more robust
> than
>
> * at-probe-time: mask all IRQs and reset IRQ status
>
> * when doing a specific operation:
> 1/ reset irq status
> 2/ unmask relevant irqs (based on the operation you're doing)
> 3/ launch the operation
> 4/ wait for interrupts
> 5/ mask irqs and check the wait_for_completion() return code + irq
> status
>
> This approach shouldn't be racy, because you're resetting+unmasking
> irqs before starting the real operation (the one supposed to generate
> such interrupts). By doing that you also get rid of the extra
> ->irq_status field, and you don't have to check irq_status before
> calling wait_for_completion().
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.
wait_for_completion_timeout() may bail out with timeout error,
then proceed to denali_reset_irq() for the next operation.
Afterwards, the event actually may happen, and invoke IRQ handler.
denali_reset_irq() and denali_isr() compete to grab the spin lock.
If denali_reset_irq() wins, it clears INTR_STATUS register
(if implemented like you suggested first) or changes IRQ mask for the
next event.
After that, denali_isr enters the critical section and checks IRQ bit
but at this moment, the IRQ bit has gone. So, it assumes this event
is not for Denali, so returns IRQ_NONE. Nobody returns IRQ_HANDLED.
Then, kernel will complain "irq *: nobody cared"
In my opinion, IRQ should be checked and cleared in one place
(in IRQ handler).
Enabling/disabling IRQ mask is not problem unless it masks out
already-asserted IRQ status bits.
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2017-06-08 12:58 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-07 11:52 [PATCH v5 00/23] mtd: nand: denali: Denali NAND IP patch bomb Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 01/23] mtd: nand: add generic helpers to check, match, maximize ECC settings Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 02/23] mtd: nand: add a shorthand to generate nand_ecc_caps structure Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 03/23] mtd: nand: denali: avoid hard-coding ECC step, strength, bytes Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 04/23] mtd: nand: denali: remove Toshiba and Hynix specific fixup code Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 05/23] mtd: nand: denali_dt: add compatible strings for UniPhier SoC variants Masahiro Yamada
2017-06-07 19:01 ` Rob Herring
2017-06-07 11:52 ` [PATCH v5 06/23] mtd: nand: denali: set NAND_ECC_CUSTOM_PAGE_ACCESS Masahiro Yamada
2017-06-07 13:26 ` Boris Brezillon
2017-06-08 7:32 ` Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 07/23] mtd: nand: denali: do not propagate NAND_STATUS_FAIL to waitfunc() Masahiro Yamada
2017-06-07 13:33 ` Boris Brezillon
2017-06-08 6:11 ` Masahiro Yamada
2017-06-08 7:05 ` Boris Brezillon
2017-06-08 9:43 ` Masahiro Yamada
2017-06-08 10:04 ` Boris Brezillon
2017-06-07 11:52 ` [PATCH v5 08/23] mtd: nand: denali: remove unneeded find_valid_banks() Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 09/23] mtd: nand: denali: handle timing parameters by setup_data_interface() Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 10/23] mtd: nand: denali: rework interrupt handling Masahiro Yamada
2017-06-07 13:57 ` Boris Brezillon
2017-06-08 6:10 ` Masahiro Yamada
2017-06-08 7:12 ` Boris Brezillon
2017-06-08 10:41 ` Masahiro Yamada
2017-06-08 11:26 ` Boris Brezillon
2017-06-08 12:58 ` Masahiro Yamada [this message]
2017-06-08 15:43 ` Boris Brezillon
2017-06-08 17:26 ` Masahiro Yamada
2017-06-08 17:30 ` Masahiro Yamada
2017-06-09 7:58 ` Boris Brezillon
2017-06-13 4:41 ` Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 11/23] mtd: nand: denali: fix NAND_CMD_STATUS handling Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 12/23] mtd: nand: denali: fix NAND_CMD_PARAM handling Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 13/23] mtd: nand: denali: switch over to cmd_ctrl instead of cmdfunc Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 14/23] mtd: nand: denali: fix bank reset function to detect the number of chips Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 15/23] mtd: nand: denali: use interrupt instead of polling for bank reset Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 16/23] mtd: nand: denali: propagate page to helpers via function argument Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 17/23] mtd: nand: denali: merge struct nand_buf into struct denali_nand_info Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 18/23] mtd: nand: denali: use flag instead of register macro for direction Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 19/23] mtd: nand: denali: fix raw and oob accessors for syndrome page layout Masahiro Yamada
2017-06-07 14:09 ` Boris Brezillon
2017-06-08 11:22 ` Masahiro Yamada
2017-06-13 4:42 ` Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 20/23] mtd: nand: denali: support hardware-assisted erased page detection Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 21/23] mtd: nand: denali: skip driver internal bounce buffer when possible Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 22/23] mtd: nand: denali: use non-managed kmalloc() for DMA buffer Masahiro Yamada
2017-06-07 11:52 ` [PATCH v5 23/23] mtd: nand: denali: enable bad block table scan Masahiro Yamada
2017-06-08 6:16 ` [PATCH v5 00/23] mtd: nand: denali: Denali NAND IP patch bomb Masahiro Yamada
2017-06-08 7:12 ` Masahiro Yamada
2017-06-08 7:18 ` Boris Brezillon
2017-06-11 20:14 ` Boris Brezillon
2017-06-08 7:14 ` Boris Brezillon
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