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Subject: Re: [PATCH 2/3] PCI: dwc: pci-dra7xx: Improve MSI IRQ handling
From:   Vignesh R <vigneshr@ti.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
CC:     Jingoo Han <jingoohan1@gmail.com>,
        Joao Pinto <Joao.Pinto@synopsys.com>,
        KISHON VIJAY ABRAHAM <kishon@ti.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Niklas Cassel <niklas.cassel@axis.com>,
        "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20180209120415.17590-1-vigneshr@ti.com>
 <20180209120415.17590-3-vigneshr@ti.com>
 <20180212175801.GA29070@e107981-ln.cambridge.arm.com>
 <7cfa73af-09fa-d298-aaab-3e74ee7e1dd5@ti.com>
Message-ID: <c3efe768-8934-16cc-142b-bc46b88fe399@ti.com>
Date:   Thu, 1 Mar 2018 21:01:53 +0530
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Hi Lorenzo,

On 15-Feb-18 9:59 AM, 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@ti.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
> status register before exiting handler. Otherwise next MSI IRQ will not
> be latched by the wrapper.
> 
> 

Did above explanation clarify CONF_IRQSTATUS_MSI register usage and the
need for IRQ handler? Are you okay with this fix?

Regards
Vignesh

>>
>> 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. 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
>>>
>