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Message-ID: <20220911154516.tu2b7qhsnk6mdtui@pali>
Date: Sun, 11 Sep 2022 17:45:16 +0200
From: Pali Rohár <pali@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Rob Herring <robh@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH] PCI: mvebu: Use devm_request_irq() for registering
interrupt handler
On Monday 29 August 2022 18:51:09 Pali Rohár wrote:
> On Sunday 10 July 2022 02:06:59 Pali Rohár wrote:
> > On Saturday 09 July 2022 18:44:30 Bjorn Helgaas wrote:
> > > [+cc Marc, since he commented on this]
> > >
> > > On Sat, Jul 09, 2022 at 04:31:51PM +0200, Pali Rohár wrote:
> > > > On Friday 01 July 2022 16:29:41 Pali Rohár wrote:
> > > > > On Thursday 23 June 2022 11:27:47 Bjorn Helgaas wrote:
> > > > > > On Tue, May 24, 2022 at 02:28:17PM +0200, Pali Rohár wrote:
> > > > > > > Same as in commit a3b69dd0ad62 ("Revert "PCI: aardvark: Rewrite IRQ code to
> > > > > > > chained IRQ handler"") for pci-aardvark driver, use devm_request_irq()
> > > > > > > instead of chained IRQ handler in pci-mvebu.c driver.
> > > > > > >
> > > > > > > This change fixes affinity support and allows to pin interrupts from
> > > > > > > different PCIe controllers to different CPU cores.
> > > > > >
> > > > > > Several other drivers use irq_set_chained_handler_and_data(). Do any
> > > > > > of them need similar changes? The commit log suggests that using
> > > > > > chained IRQ handlers breaks affinity support. But perhaps that's not
> > > > > > the case and the real culprit is some other difference between mvebu
> > > > > > and the other drivers.
> > > > >
> > > > > And there is another reason to not use irq_set_chained_handler_and_data
> > > > > and instead use devm_request_irq(). Armada XP has some interrupts
> > > > > shared and it looks like that irq_set_chained_handler_and_data() API
> > > > > does not handle shared interrupt sources too.
> > > > >
> > > > > I can update commit message to mention also this fact.
> > > >
> > > > Anything needed from me to improve this fix?
> > >
> > > My impression from Marc's response [1] was that this patch would
> > > "break the contract the kernel has with userspace" and he didn't think
> > > this was acceptable. But maybe I'm not understanding it correctly.
> >
> > This is argument which Marc use when he does not have any argument.
> >
> > Support for dedicated INTx into pci-mvebu.c was introduced just recently
> > and I used irq_set_chained_handler_and_data() just because I thought it
> > is a good idea and did not know about all those issues with it. So there
> > cannot be any breakage by this patch.
> >
> > I already converted other pci-aardvark.c driver to use
> > irq_set_chained_handler_and_data() API because wanted it... But at the
> > end _that conversion_ caused breakage of afinity support and so this
> > conversion had to be reverted:
> > https://lore.kernel.org/linux-pci/20220515125815.30157-1-pali@kernel.org/#t
> >
> > Based on his past decisions, above suggestions which cause _real_
> > breakage and his expressions like mvebu should be put into the trash,
> > I'm not going to listen him anymore. The only breaking is done by him.
> >
> >
> > There are two arguments why to not use irq_set_chained_handler_and_data:
> >
> > 1) It does not support afinity and therefore has negative performance
> > impact on Armada platforms with more CPUs and more PCIe ports.
> >
> > 2) It does not support shared interrupts and therefore it will break
> > hardware on which interrupt lines are shares (mostly Armada XP).
> >
> > So these issues have to be fixed and currently I see only option to
> > switch irq_set_chained_handler_and_data() to devm_request_irq() which I
> > did in this fixup patch.
>
> Any progress here? This patch is waiting here since end of May and if
> something is going to be broken then it is this fact of ignoring reported
> issues and proposed patch. Do you better solution how to fix commit
> ec075262648f?
After two weeks I'm reminding this fix patch again...
> > > In any event, I'm waiting for you to continue that discussion. Maybe
> > > there's an argument for doing this even though it breaks some
> > > userspace expectations. If so, that should be acknowledged and
> > > explained. Or maybe there's an alternative implementation. Marc
> > > gave a link to some suggestions [2], which I haven't looked into, but
> > > maybe you could.
> >
> > Once Marc fix/implement that alternative implementation in his codebase
> > then we can continue discuss this direction. Until that happens I think
> > there is no other way, at least I do not see them.
> >
> > And I'm not going to work again any patch for him and his codebase as he
> > explicitly expressed that is against any improvements in mvebu drivers
> > and is rejecting (my) patches. This is just waste of my time. So sorry.
> >
> > > [1] https://lore.kernel.org/r/874k0bf7f7.wl-maz@kernel.org
> > > [2] https://lore.kernel.org/all/20220502102137.764606ee@thinkpad/
> > >
> > > > > > > Fixes: ec075262648f ("PCI: mvebu: Implement support for legacy INTx interrupts")
> > > > > > > Signed-off-by: Pali Rohár <pali@...nel.org>
> > > > > > > ---
> > > > > > > Hello Bjorn! This is basically same issue as for pci-aardvark.c:
> > > > > > > https://lore.kernel.org/linux-pci/20220515125815.30157-1-pali@kernel.org/#t
> > > > > > >
> > > > > > > I tested this patch with pci=nomsi in cmdline (to force kernel to use
> > > > > > > legacy intx instead of MSI) on A385 and checked that I can set affinity
> > > > > > > via /proc/irq/XX/smp_affinity file for every mvebu pcie controller to
> > > > > > > different CPU and legacy interrupts from different cards/controllers
> > > > > > > were handled by different CPUs.
> > > > > > >
> > > > > > > I think that this is important on Armada XP platforms which have many
> > > > > > > independent PCIe controllers (IIRC up to 10) and many cores (up to 4).
> > > > > > > ---
> > > > > > > drivers/pci/controller/pci-mvebu.c | 30 +++++++++++++++++-------------
> > > > > > > 1 file changed, 17 insertions(+), 13 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
> > > > > > > index 8f76d4bda356..de67ea39fea5 100644
> > > > > > > --- a/drivers/pci/controller/pci-mvebu.c
> > > > > > > +++ b/drivers/pci/controller/pci-mvebu.c
> > > > > > > @@ -1017,16 +1017,13 @@ static int mvebu_pcie_init_irq_domain(struct mvebu_pcie_port *port)
> > > > > > > return 0;
> > > > > > > }
> > > > > > >
> > > > > > > -static void mvebu_pcie_irq_handler(struct irq_desc *desc)
> > > > > > > +static irqreturn_t mvebu_pcie_irq_handler(int irq, void *arg)
> > > > > > > {
> > > > > > > - struct mvebu_pcie_port *port = irq_desc_get_handler_data(desc);
> > > > > > > - struct irq_chip *chip = irq_desc_get_chip(desc);
> > > > > > > + struct mvebu_pcie_port *port = arg;
> > > > > > > struct device *dev = &port->pcie->pdev->dev;
> > > > > > > u32 cause, unmask, status;
> > > > > > > int i;
> > > > > > >
> > > > > > > - chained_irq_enter(chip, desc);
> > > > > > > -
> > > > > > > cause = mvebu_readl(port, PCIE_INT_CAUSE_OFF);
> > > > > > > unmask = mvebu_readl(port, PCIE_INT_UNMASK_OFF);
> > > > > > > status = cause & unmask;
> > > > > > > @@ -1040,7 +1037,7 @@ static void mvebu_pcie_irq_handler(struct irq_desc *desc)
> > > > > > > dev_err_ratelimited(dev, "unexpected INT%c IRQ\n", (char)i+'A');
> > > > > > > }
> > > > > > >
> > > > > > > - chained_irq_exit(chip, desc);
> > > > > > > + return status ? IRQ_HANDLED : IRQ_NONE;
> > > > > > > }
> > > > > > >
> > > > > > > static int mvebu_pcie_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
> > > > > > > @@ -1490,9 +1487,20 @@ static int mvebu_pcie_probe(struct platform_device *pdev)
> > > > > > > mvebu_pcie_powerdown(port);
> > > > > > > continue;
> > > > > > > }
> > > > > > > - irq_set_chained_handler_and_data(irq,
> > > > > > > - mvebu_pcie_irq_handler,
> > > > > > > - port);
> > > > > > > +
> > > > > > > + ret = devm_request_irq(dev, irq, mvebu_pcie_irq_handler,
> > > > > > > + IRQF_SHARED | IRQF_NO_THREAD,
> > > > > > > + port->name, port);
> > > > > > > + if (ret) {
> > > > > > > + dev_err(dev, "%s: cannot register interrupt handler: %d\n",
> > > > > > > + port->name, ret);
> > > > > > > + irq_domain_remove(port->intx_irq_domain);
> > > > > > > + pci_bridge_emul_cleanup(&port->bridge);
> > > > > > > + devm_iounmap(dev, port->base);
> > > > > > > + port->base = NULL;
> > > > > > > + mvebu_pcie_powerdown(port);
> > > > > > > + continue;
> > > > > > > + }
> > > > > > > }
> > > > > > >
> > > > > > > /*
> > > > > > > @@ -1599,7 +1607,6 @@ static int mvebu_pcie_remove(struct platform_device *pdev)
> > > > > > >
> > > > > > > for (i = 0; i < pcie->nports; i++) {
> > > > > > > struct mvebu_pcie_port *port = &pcie->ports[i];
> > > > > > > - int irq = port->intx_irq;
> > > > > > >
> > > > > > > if (!port->base)
> > > > > > > continue;
> > > > > > > @@ -1615,9 +1622,6 @@ static int mvebu_pcie_remove(struct platform_device *pdev)
> > > > > > > /* Clear all interrupt causes. */
> > > > > > > mvebu_writel(port, ~PCIE_INT_ALL_MASK, PCIE_INT_CAUSE_OFF);
> > > > > > >
> > > > > > > - if (irq > 0)
> > > > > > > - irq_set_chained_handler_and_data(irq, NULL, NULL);
> > > > > > > -
> > > > > > > /* Remove IRQ domains. */
> > > > > > > if (port->intx_irq_domain)
> > > > > > > irq_domain_remove(port->intx_irq_domain);
> > > > > > > --
> > > > > > > 2.20.1
> > > > > > >
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