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Message-ID: <CAAd53p4EWEuu-V5hvOHtKZQxCJNf94+FOJT+_ryu0s2RpB1o-Q@mail.gmail.com>
Date: Tue, 3 Sep 2024 15:07:45 +0800
From: Kai-Heng Feng <kai.heng.feng@...onical.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
acelan.kao@...onical.com, lpieralisi@...nel.org, kw@...ux.com,
robh@...nel.org, bhelgaas@...gle.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: vmd: Delay interrupt handling on MTL VMD controller
On Tue, Sep 3, 2024 at 12:29 PM Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.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.
>
> > 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@...onical.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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