Re: [PATCH] PCI: vmd: Delay interrupt handling on MTL VMD controller

[Kai-Heng Feng]

On Tue, Sep 3, 2024 at 12:29 PM Manivannan Sadhasivam
<manivannan.sadhasivam@xxxxxxxxxx> wrote:
>
> On Tue, Sep 03, 2024 at 10:55:44AM +0800, Kai-Heng Feng wrote:
> > Meteor Lake VMD has a bug that the IRQ raises before the DMA region is
> > ready, so the requested IO is considered never completed:
> > [   97.343423] nvme nvme0: I/O 259 QID 2 timeout, completion polled
> > [   97.343446] nvme nvme0: I/O 384 QID 3 timeout, completion polled
> > [   97.343459] nvme nvme0: I/O 320 QID 4 timeout, completion polled
> > [   97.343470] nvme nvme0: I/O 707 QID 5 timeout, completion polled
> >
> > The is documented as erratum MTL016 [0]. The suggested workaround is to
> > "The VMD MSI interrupt-handler should initially perform a dummy register
> > read to the MSI initiator device prior to any writes to ensure proper
> > PCIe ordering." which essentially is adding a delay before the interrupt
> > handling.
> >
>
> Why can't you add a dummy register read instead? Adding a delay for PCIe
> ordering is not going to work always.

This can be done too. But it can take longer than 4us delay, so I'd
like to keep it a bit faster here.

>
> > Hence add a delay before handle interrupt to workaround the erratum.
> >
> > [0] https://edc.intel.com/content/www/us/en/design/products/platforms/details/meteor-lake-u-p/core-ultra-processor-specification-update/errata-details/#MTL016
> >
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217871
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > ---
> >  drivers/pci/controller/vmd.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > index a726de0af011..3433b3730f9c 100644
> > --- a/drivers/pci/controller/vmd.c
> > +++ b/drivers/pci/controller/vmd.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/srcu.h>
> >  #include <linux/rculist.h>
> >  #include <linux/rcupdate.h>
> > +#include <linux/delay.h>
> >
> >  #include <asm/irqdomain.h>
> >
> > @@ -74,6 +75,9 @@ enum vmd_features {
> >        * proper power management of the SoC.
> >        */
> >       VMD_FEAT_BIOS_PM_QUIRK          = (1 << 5),
> > +
> > +     /* Erratum MTL016 */
> > +     VMD_FEAT_INTERRUPT_QUIRK        = (1 << 6),
> >  };
> >
> >  #define VMD_BIOS_PM_QUIRK_LTR        0x1003  /* 3145728 ns */
> > @@ -90,6 +94,8 @@ static DEFINE_IDA(vmd_instance_ida);
> >   */
> >  static DEFINE_RAW_SPINLOCK(list_lock);
> >
> > +static bool interrupt_delay;
> > +
> >  /**
> >   * struct vmd_irq - private data to map driver IRQ to the VMD shared vector
> >   * @node:    list item for parent traversal.
> > @@ -105,6 +111,7 @@ struct vmd_irq {
> >       struct vmd_irq_list     *irq;
> >       bool                    enabled;
> >       unsigned int            virq;
> > +     bool                    delay_irq;
>
> This is unused. Perhaps you wanted to use this instead of interrupt_delay?

This is leftover, will scratch this.

Kai-Heng

>
> - Mani
>
> >  };
> >
> >  /**
> > @@ -680,8 +687,11 @@ static irqreturn_t vmd_irq(int irq, void *data)
> >       int idx;
> >
> >       idx = srcu_read_lock(&irqs->srcu);
> > -     list_for_each_entry_rcu(vmdirq, &irqs->irq_list, node)
> > +     list_for_each_entry_rcu(vmdirq, &irqs->irq_list, node) {
> > +             if (interrupt_delay)
> > +                     udelay(4);
> >               generic_handle_irq(vmdirq->virq);
> > +     }
> >       srcu_read_unlock(&irqs->srcu, idx);
> >
> >       return IRQ_HANDLED;
> > @@ -1015,6 +1025,9 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >       if (features & VMD_FEAT_OFFSET_FIRST_VECTOR)
> >               vmd->first_vec = 1;
> >
> > +     if (features & VMD_FEAT_INTERRUPT_QUIRK)
> > +             interrupt_delay = true;
> > +
> >       spin_lock_init(&vmd->cfg_lock);
> >       pci_set_drvdata(dev, vmd);
> >       err = vmd_enable_domain(vmd, features);
> > @@ -1106,7 +1119,8 @@ static const struct pci_device_id vmd_ids[] = {
> >       {PCI_VDEVICE(INTEL, 0xa77f),
> >               .driver_data = VMD_FEATS_CLIENT,},
> >       {PCI_VDEVICE(INTEL, 0x7d0b),
> > -             .driver_data = VMD_FEATS_CLIENT,},
> > +             .driver_data = VMD_FEATS_CLIENT |
> > +                            VMD_FEAT_INTERRUPT_QUIRK,},
> >       {PCI_VDEVICE(INTEL, 0xad0b),
> >               .driver_data = VMD_FEATS_CLIENT,},
> >       {PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_VMD_9A0B),
> > --
> > 2.43.0
> >
>
> --
> மணிவண்ணன் சதாசிவம்