Messages in this thread | | | Subject | Re: [PATCH] irqchip/sifive-plic: add irq_mask and irq_unmask | From | Darius Rad <> | Date | Mon, 16 Sep 2019 15:04:56 -0400 |
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On 9/15/19 2:20 PM, Marc Zyngier wrote: > On Sun, 15 Sep 2019 18:31:33 +0100, > Palmer Dabbelt <palmer@sifive.com> wrote: > > Hi Palmer, > >> >> On Sun, 15 Sep 2019 07:24:20 PDT (-0700), maz@kernel.org wrote: >>> On Thu, 12 Sep 2019 22:40:34 +0100, >>> Darius Rad <darius@bluespec.com> wrote: >>> >>> Hi Darius, >>> >>>> >>>> As per the existing comment, irq_mask and irq_unmask do not need >>>> to do anything for the PLIC. However, the functions must exist >>>> (the pointers cannot be NULL) as they are not optional, based on >>>> the documentation (Documentation/core-api/genericirq.rst) as well >>>> as existing usage (e.g., include/linux/irqchip/chained_irq.h). >>>> >>>> Signed-off-by: Darius Rad <darius@bluespec.com> >>>> --- >>>> drivers/irqchip/irq-sifive-plic.c | 13 +++++++++---- >>>> 1 file changed, 9 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c >>>> index cf755964f2f8..52d5169f924f 100644 >>>> --- a/drivers/irqchip/irq-sifive-plic.c >>>> +++ b/drivers/irqchip/irq-sifive-plic.c >>>> @@ -111,6 +111,13 @@ static void plic_irq_disable(struct irq_data *d) >>>> plic_irq_toggle(cpu_possible_mask, d->hwirq, 0); >>>> } >>>> +/* >>>> + * There is no need to mask/unmask PLIC interrupts. They are "masked" >>>> + * by reading claim and "unmasked" when writing it back. >>>> + */ >>>> +static void plic_irq_mask(struct irq_data *d) { } >>>> +static void plic_irq_unmask(struct irq_data *d) { } >>> >>> This outlines a bigger issue. If your irqchip doesn't require >>> mask/unmask, you're probably not using the right interrupt >>> flow. Looking at the code, I see you're using handle_simple_irq, which >>> is almost universally wrong. >>> >>> As per the description above, these interrupts should be using the >>> fasteoi flow, which is designed for this exact behaviour (the >>> interrupt controller knows which interrupt is in flight and doesn't >>> require SW to do anything bar signalling the EOI). >>> >>> Another thing is that mask/unmask tends to be a requirement, while >>> enable/disable tends to be optional. There is no hard line here, but >>> the expectations are that: >>> >>> (a) A disabled line can drop interrupts >>> (b) A masked line cannot drop interrupts >>> >>> Depending what the PLIC architecture mandates, you'll need to >>> implement one and/or the other. Having just (a) is indicative of a HW >>> bug, and I'm not assuming that this is the case. (b) only is pretty >>> common, and (a)+(b) has a few adepts. My bet is that it requires (b) >>> only. >>> >>>> + >>>> #ifdef CONFIG_SMP >>>> static int plic_set_affinity(struct irq_data *d, >>>> const struct cpumask *mask_val, bool force) >>>> @@ -138,12 +145,10 @@ static int plic_set_affinity(struct irq_data *d, >>>> static struct irq_chip plic_chip = { >>>> .name = "SiFive PLIC", >>>> - /* >>>> - * There is no need to mask/unmask PLIC interrupts. They are "masked" >>>> - * by reading claim and "unmasked" when writing it back. >>>> - */ >>>> .irq_enable = plic_irq_enable, >>>> .irq_disable = plic_irq_disable, >>>> + .irq_mask = plic_irq_mask, >>>> + .irq_unmask = plic_irq_unmask, >>>> #ifdef CONFIG_SMP >>>> .irq_set_affinity = plic_set_affinity, >>>> #endif >>> >>> Can you give the following patch a go? It brings the irq flow in line >>> with what the HW can do. It is of course fully untested (not even >>> compile tested...). >>> >>> Thanks, >>> >>> M. >>> >>> From c0ce33a992ec18f5d3bac7f70de62b1ba2b42090 Mon Sep 17 00:00:00 2001 >>> From: Marc Zyngier <maz@kernel.org> >>> Date: Sun, 15 Sep 2019 15:17:45 +0100 >>> Subject: [PATCH] irqchip/sifive-plic: Switch to fasteoi flow >>> >>> The SiFive PLIC interrupt controller seems to have all the HW >>> features to support the fasteoi flow, but the driver seems to be >>> stuck in a distant past. Bring it into the 21st century. >> >> Thanks. We'd gotten these comments during the review process but >> nobody had gotten the time to actually fix the issues. > > No worries. The IRQ subsystem is an acquired taste... ;-) > >>> >>> Signed-off-by: Marc Zyngier <maz@kernel.org> >>> --- >>> drivers/irqchip/irq-sifive-plic.c | 29 +++++++++++++++-------------- >>> 1 file changed, 15 insertions(+), 14 deletions(-) >>> >>> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c >>> index cf755964f2f8..8fea384d392b 100644 >>> --- a/drivers/irqchip/irq-sifive-plic.c >>> +++ b/drivers/irqchip/irq-sifive-plic.c >>> @@ -97,7 +97,7 @@ static inline void plic_irq_toggle(const struct cpumask *mask, >>> } >>> } >>> -static void plic_irq_enable(struct irq_data *d) >>> +static void plic_irq_mask(struct irq_data *d) > > Of course, this is wrong. The perks of trying to do something at the > last minute while boarding an airplane. Don't do that. > > This should of course read "plic_irq_unmask"... > >>> { >>> unsigned int cpu = cpumask_any_and(irq_data_get_affinity_mask(d), >>> cpu_online_mask); >>> @@ -106,7 +106,7 @@ static void plic_irq_enable(struct irq_data *d) >>> plic_irq_toggle(cpumask_of(cpu), d->hwirq, 1); >>> } >>> -static void plic_irq_disable(struct irq_data *d) >>> +static void plic_irq_unmask(struct irq_data *d) > > ... and this should be "plic_irq_mask". > > [...] > >> Reviewed-by: Palmer Dabbelt <palmer@sifive.com> >> Tested-by: Palmer Dabbelt <palmer@sifive.com> (QEMU Boot) > > Huhuh... It may be that QEMU doesn't implement the full-fat PLIC, as > the above bug should have kept the IRQ lines masked. > >> We should test them on the hardware, but I don't have any with me >> right now. David's probably in the best spot to do this, as he's got >> a setup that does all the weird interrupt sources (ie, PCIe). >> >> David: do you mind testing this? I've put the patch here: >> >> ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git >> -b plic-fasteoi > > I've pushed out a branch with the fixed patch: > > git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git irq/plic-fasteoi >
That patch works for me on real-ish hardware. I tried on two FPGA systems that have different PLIC implementations. Both include a PCIe root port (and associated interrupt source). So for whatever it's worth:
Tested-by: Darius Rad <darius@bluespec.com>
> Thanks, > > M. >
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