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Message-ID: <20180315181043.GA12772@red-moon>
Date: Thu, 15 Mar 2018 18:10:43 +0000
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Vignesh R <vigneshr@...com>
Cc: Jingoo Han <jingoohan1@...il.com>,
Joao Pinto <Joao.Pinto@...opsys.com>,
KISHON VIJAY ABRAHAM <kishon@...com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Niklas Cassel <niklas.cassel@...s.com>,
"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
gustavo.pimentel@...opsys.com
Subject: Re: [PATCH 2/3] PCI: dwc: pci-dra7xx: Improve MSI IRQ handling
[CC'ed Gustavo]
On Fri, Mar 09, 2018 at 09:53:24AM +0530, Vignesh R wrote:
>
>
> On Tuesday 06 March 2018 08:42 PM, Lorenzo Pieralisi wrote:
> > On Thu, Feb 15, 2018 at 09:59:21AM +0530, Vignesh R wrote:
> >> Hi,
> >>
> >> On Monday 12 February 2018 11:28 PM, Lorenzo Pieralisi wrote:
> >>> On Fri, Feb 09, 2018 at 05:34:14PM +0530, Vignesh R wrote:
> >>>> We need to ensure that there are no pending MSI IRQ vector set (i.e
> >>>> PCIE_MSI_INTR0_STATUS reads 0 at least once) before exiting
> >>>> dra7xx_pcie_msi_irq_handler(). Else, the dra7xx PCIe wrapper will not
> >>>> register new MSI IRQs even though PCIE_MSI_INTR0_STATUS shows IRQs are
> >>>> pending. Therefore, keep calling dra7xx_pcie_msi_irq_handler() until it
> >>>> returns IRQ_NONE, which suggests that PCIE_MSI_INTR0_STATUS is 0.
> >>>>
> >>>> This fixes a bug, where PCIe wifi cards with 4 DMA queues like Intel
> >>>> 8260 used to throw following error and stall during ping/iperf3 tests.
> >>>>
> >>>> [ 97.776310] iwlwifi 0000:01:00.0: Queue 9 stuck for 2500 ms.
> >>>>
> >>>> Signed-off-by: Vignesh R <vigneshr@...com>
> >>>> ---
> >>>> drivers/pci/dwc/pci-dra7xx.c | 21 ++++++++++++++++++---
> >>>> 1 file changed, 18 insertions(+), 3 deletions(-)
> >>>>
> >>>> diff --git a/drivers/pci/dwc/pci-dra7xx.c b/drivers/pci/dwc/pci-dra7xx.c
> >>>> index ed8558d638e5..3420cbf7b60a 100644
> >>>> --- a/drivers/pci/dwc/pci-dra7xx.c
> >>>> +++ b/drivers/pci/dwc/pci-dra7xx.c
> >>>> @@ -254,14 +254,31 @@ static irqreturn_t dra7xx_pcie_msi_irq_handler(int irq, void *arg)
> >>>> struct dra7xx_pcie *dra7xx = arg;
> >>>> struct dw_pcie *pci = dra7xx->pci;
> >>>> struct pcie_port *pp = &pci->pp;
> >>>> + int count = 0;
> >>>> unsigned long reg;
> >>>> u32 virq, bit;
> >>>>
> >>>> reg = dra7xx_pcie_readl(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI);
> >>>> + dra7xx_pcie_writel(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI, reg);
> >>>>
> >>>> switch (reg) {
> >>>> case MSI:
> >>>> - dw_handle_msi_irq(pp);
> >>>> + /*
> >>>> + * Need to make sure no MSI IRQs are pending before
> >>>> + * exiting handler, else the wrapper will not catch new
> >>>> + * IRQs. So loop around till dw_handle_msi_irq() returns
> >>>> + * IRQ_NONE
> >>>> + */
> >>>> + while (dw_handle_msi_irq(pp) != IRQ_NONE && count < 1000)
> >>>> + count++;
> >>>> +
> >>>> + if (count == 1000) {
> >>>> + dev_err(pci->dev, "too much work in msi irq\n");
> >>>> + dra7xx_pcie_writel(dra7xx,
> >>>> + PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI,
> >>>> + reg);
> >>>> + return IRQ_HANDLED;
> >>>
> >>> I am not merging any code patching this IRQ handling routine anymore
> >>> unless you thoroughly explain to me how this CONF_IRQSTATUS_MSI register
> >>> works (and how it is related to DW registers) and why this specific host
> >>> controller needs handling that is not required by any other host
> >>> controller relying on dw_handle_msi_irq().
> >>
> >> Unlike other DW PCIe controllers, TI implementation has a wrapper on top
> >> of DW core. This wrapper latches the DW core level MSI and legacy
> >> interrupts and then propagates it to GIC.
> >> PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI register is present in this TI
> >> wrapper which aggregates all the MSI IRQs(PCIE_MSI_INTR0_STATUS) of DW
> >> level. They are mapped on the MSI interrupt line of PCIe controller,
> >> using a single status bit in the PCIECTRL_TI_CONF_IRQSTATUS_MSI register.
> >>
> >> So, the irq handler, dra7xx_pcie_msi_irq_handler(), first needs to look
> >> at PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI[4] to know that its MSI IRQ and
> >> then call dw_handle_msi_irq() to handle individual MSI vectors.
> >> Driver has to make sure there are no pending vectors in DW core MSI
> >
> > How can it make *sure* ? And what makes the wrapper latch MSI IRQs
> > again ?
> >
>
> This is the sequence that I got from discussion with internal HW team:
> 1. read CONF_IRQSTATUS_MSI in wrapper and check if MSI bit
> 2. clear CONF_IRQSTATUS_MSI
> 3. read, clear and handle PCIE_MSI_INTR0_STATUS vectors
> 4. repeat step 3 until PCIE_MSI_INTR0_STATUS reads 0
>
> If read of PCIE_MSI_INTR0_STATUS returns 0 at least once, then its
> guaranteed that the next time any vector is set in PCIE_MSI_INTR0_STATUS
> register(due to MSI IRQ), wrapper will latch it and raise an IRQ to CPU.
>
>
> >> status register before exiting handler. Otherwise next MSI IRQ will not
> >> be latched by the wrapper.
Hi Vignesh,
thank you for explaining. To me - this looks like it is better to write
a separate IRQ chip implementation for DRA7XX, let's face it this patch
is a bit hackish (and will prevent us from removing dw_handle_msi_irq()
altogether - which is something we want to achieve) and it is clutching
at straws to re-use DWC MSI code but honestly it is a bit of stretch.
This would duplicate some code, yes but on the other hand it would
give you full control of the (DWC) HW.
You can have a look at pcie-tango.c or the mobiveil patches I have
just reviewed:
https://patchwork.ozlabs.org/patch/878494/
Please note Gustavo's reworked DWC MSI handling that is now queued
for v4.17 in my pci/dwc-msi branch - please do have a look at it
too (and if Gustavo has comments they are welcome).
I do not like the current implementation - sorry, we have to come
up with something cleaner, I do not think that's so complicated.
I do not mind reviewing intermediate patches as long as we get to
a cleaner solution.
Thanks,
Lorenzo
> >
> > I am sorry but I do not understand how this works - what is the
> > condition that makes wrapper latch IRQs again ? This is at least
> > racy, if not outright broken.
> >
> > That count == 1000 is a symptom there is something broken on how this
> > driver handles IRQs and I have the impression that we are applying
> > plasters on top of plasters to make it less broken than it actually is.
> >
>
> It is an upper bound on how many times driver looks at
> PCIE_MSI_INTR0_STATUS register, so that there is no infinite looping
> when there is an IRQ flood due to misbehaving EP. count == 1000
> condition should not happen and it means something is wrong in the
> system. I haven't hit this situation in testing
> I can either remove this or put a WARN_ON to say this situation should
> not have happened, if that makes you more comfortable with the patch.
>
>
> >>> I suspect there is a code design flaw with the way this host handles
> >>> IRQs and we are going to find it and fix it the way it should, not with
> >>> any plaster like this patch.
> >>>
> >>
> >> I agree there has been some churn wrt this wrapper level IRQ handler.
> >> But, that was because hardware documentation/TRM did not match
> >> actual behavior and so it took some time to understand how the
> >> hardware is working.
> >
> > How does HW work :) ? Please explain in detail how this works in HW
> > then we will get to the code.
> >
>
> Software needs to ensure that PCIE_MSI_INTR0_STATUS needs be 0 by
> reading it. Then, when the next MSI IRQ is raised CONF_IRQSTATUS_MSI
> register in the wrapper will latch the next IRQ.
>
> This is my current knowledge, let me know if you need to know anything
> specifically, I will try to ask HW team.
>
> Regards
> Vignesh
>
> > Thanks,
> > Lorenzo
> >
> >> I have extensively tested this series on multiple problematic PCIe USB
> >> cards and PCIe WiFi cards over week long stress tests. And also had
> >> some agreement with internal hardware designers. Hardware
> >> documentations will also be updated.
> >>
> >>
> >>> Lorenzo
> >>>
> >>>> + }
> >>>> break;
> >>>> case INTA:
> >>>> case INTB:
> >>>> @@ -275,8 +292,6 @@ static irqreturn_t dra7xx_pcie_msi_irq_handler(int irq, void *arg)
> >>>> break;
> >>>> }
> >>>>
> >>>> - dra7xx_pcie_writel(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI, reg);
> >>>> -
> >>>> return IRQ_HANDLED;
> >>>> }
> >>>>
> >>>> --
> >>>> 2.16.1
> >>>>
> >>
> >> --
> >> Regards
> >> Vignesh
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