Re: [PATCH 2/3] PCI: dwc: pci-dra7xx: Improve MSI IRQ handling

[Lorenzo Pieralisi]

On Thu, Mar 01, 2018 at 09:01:53PM +0530, Vignesh R wrote:
> 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@xxxxxx>
> >>> ---
> >>>   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?

Hi Vignesh,

I will get back to it shortly, thanks for your patience.

Lorenzo

> 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
> >>>
> >