Messages in this thread | | | Date | Mon, 01 Nov 2021 09:25:31 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH V5 3/3] irqchip/sifive-plic: Fixup thead, c900-plic request_threaded_irq with ONESHOT |
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On Mon, 01 Nov 2021 02:20:21 +0000, Guo Ren <guoren@kernel.org> wrote: > > On Thu, Oct 28, 2021 at 10:58 PM Marc Zyngier <maz@kernel.org> wrote: > > > > On Thu, 28 Oct 2021 11:55:23 +0100, > > Nikita Shubin <nikita.shubin@maquefel.me> wrote: > > > > > > Hello Marc and Guo Ren! > > > > > > On Mon, 25 Oct 2021 11:48:33 +0100 > > > Marc Zyngier <maz@kernel.org> wrote: > > > > > > > On Sun, 24 Oct 2021 02:33:03 +0100, > > > > guoren@kernel.org wrote: > > > > > > > > > > From: Guo Ren <guoren@linux.alibaba.com> > > > > > > > > > > When using "devm_request_threaded_irq(,,,,IRQF_ONESHOT,,)" in the > > > > > driver, only the first interrupt could be handled, and continue irq > > > > > is blocked by hw. Because the thead,c900-plic couldn't complete > > > > > masked irq source which has been disabled in enable register. Add > > > > > thead_plic_chip which fix up c906-plic irq source completion > > > > > problem by unmask/mask wrapper. > > > > > > > > > > Here is the description of Interrupt Completion in PLIC spec [1]: > > > > > > > > > > The PLIC signals it has completed executing an interrupt handler by > > > > > writing the interrupt ID it received from the claim to the > > > > > claim/complete register. The PLIC does not check whether the > > > > > completion ID is the same as the last claim ID for that target. If > > > > > the completion ID does not match an interrupt source that is > > > > > currently enabled for the target, the ^^ ^^^^^^^^^ ^^^^^^^ > > > > > completion is silently ignored. > > > > > > > > Given this bit of the spec... > > > > > > > > > +static void plic_thead_irq_eoi(struct irq_data *d) > > > > > +{ > > > > > + struct plic_handler *handler = > > > > > this_cpu_ptr(&plic_handlers); + > > > > > + if (irqd_irq_masked(d)) { > > > > > + plic_irq_unmask(d); > > > > > + writel(d->hwirq, handler->hart_base + > > > > > CONTEXT_CLAIM); > > > > > + plic_irq_mask(d); > > > > > + } else { > > > > > + writel(d->hwirq, handler->hart_base + > > > > > CONTEXT_CLAIM); > > > > > + } > > > > > +} > > > > > + > > > > > > > > ... it isn't obvious to me why this cannot happen on an SiFive PLIC. > > > > > > This indeed happens with SiFive PLIC. I am currently tinkering with > > > da9063 RTC on SiFive Unmatched, and ALARM irq fires only once. However > > > with changes proposed by Guo Ren in plic_thead_irq_eoi, everything > > > begins to work fine. > > > > > > May be these change should be propagated to plic_irq_eoi instead of > > > making a new function ? > > > > That's my impression too. I think the T-Head defect is pretty much > > immaterial when you consider how 'interesting' the PLIC architecture > > is. > Which is the "T-Head defect" you mentioned here? > 1. Auto masking with claim + complete (I don't think it's a defect, > right? May I add a new patch to utilize the feature to decrease a > little duplicate mask/unmask operations in the future?)
That *is* a T-Head defect. It may not be material for Linux, but being a departure from the spec, it is a bug, clear and simple. IMHO, either you implement the spec to the letter, or you don't. If you deviate, this is something else.
> 2. EOI failed when masked
This one is a PLIC architecture defect, which seems to plague everyone.
> > > Conflating EOI and masking really is a misfeature... > I think the problem is riscv PLIC reuse enable bit as mask bit. I > recommend separating them. That means: > - EOI still depends on enable bit. > - Add mask/unmask bit regs to do the right thing.
Maybe, but that's not the problem at hand. I suggest you move architectural discussions to a separate thread, and keep this thread for fixing the mess that plagues existing users.
M.
-- Without deviation from the norm, progress is not possible.
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