Re: [PATCH] PCI: mediatek: Change MSI interrupt processing sequence

[Chen-Yu Tsai <wenst@chromium.org>]

On Mon, Jan 24, 2022 at 2:27 PM qizhong.cheng
<qizhong.cheng@mediatek.com> wrote:
>
> Hi chenYu,
>
> On Mon, 2022-01-24 at 11:12 +0800, Chen-Yu Tsai wrote:
> > Hi,
> >
> > On Sun, Jan 23, 2022 at 11:34 AM qizhong cheng
> > <qizhong.cheng@mediatek.com> wrote:
> > >
> > > As an edge-triggered interrupts, its interrupt status should be
> > > cleared
> > > before dispatch to the handler of device.
> >
> > I'm curious, is this just a code correction or are there real world
> > cases where something fails?
>
> Yes, we found a failure when used iperf tool for wifi and network cards
> performance testing. The function of "while" has just been executed,
> and the EP sent an MSI before executing "Clear MSI interrupt status".
> After executing "Clear MSI interrupt status", this edge-triggered
> interrupt status is cleared, but EP is still waiting for interrupt
> handler.

Can you also include this in the commit log?  It would be nice to record
the exact scenario that this fix targets.

ChenYu

> >
> > Also, please add a Fixes tag and maybe Cc stable so this gets
> > backported
> > automatically.
>
> Thanks for your review, I will fix it in the next version.
>
> >
> > ChenYu
> >
> > > Signed-off-by: qizhong cheng <qizhong.cheng@mediatek.com>
> > > ---
> > >  drivers/pci/controller/pcie-mediatek.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/pcie-mediatek.c
> > > b/drivers/pci/controller/pcie-mediatek.c
> > > index 2f3f974977a3..705ea33758b1 100644
> > > --- a/drivers/pci/controller/pcie-mediatek.c
> > > +++ b/drivers/pci/controller/pcie-mediatek.c
> > > @@ -624,12 +624,12 @@ static void mtk_pcie_intr_handler(struct
> > > irq_desc *desc)
> > >                 if (status & MSI_STATUS){
> > >                         unsigned long imsi_status;
> > >
> > > +                       /* Clear MSI interrupt status */
> > > +                       writel(MSI_STATUS, port->base +
> > > PCIE_INT_STATUS);
> > >                         while ((imsi_status = readl(port->base +
> > > PCIE_IMSI_STATUS))) {
> > >                                 for_each_set_bit(bit, &imsi_status,
> > > MTK_MSI_IRQS_NUM)
> > >                                         generic_handle_domain_irq(p
> > > ort->inner_domain, bit);
> > >                         }
> > > -                       /* Clear MSI interrupt status */
> > > -                       writel(MSI_STATUS, port->base +
> > > PCIE_INT_STATUS);
> > >                 }
> > >         }
> > >
> > > --
> > > 2.25.1
> > >
> > >
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>