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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Tue, Sep 03, 2024 at 03:07:45PM +0800, Kai-Heng Feng wrote:
> On Tue, Sep 3, 2024 at 12:29 PM Manivannan Sadhasivam
> <manivannan.sadhasivam@linaro.org> 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.
> 

No. As I said, this delay is not going to work all the time and highly
unreliable. Please use the register read as suggested.

- Mani

> >
> > > 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@canonical.com>
> > > ---
> > >  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

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