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Date: Tue, 29 Oct 2013 15:58:48 -0600
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
xen-devel <xen-devel@...ts.xen.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Feng Jin <joe.jin@...cle.com>,
Sucheta Chakraborty <sucheta.chakraborty@...gic.com>,
Jingoo Han <jg1.han@...sung.com>
Subject: Re: [PATCH 2/3] PCI: Refactor MSI/MSIX mask restore code to fix
interrupt lost issue
On Wed, Oct 16, 2013 at 02:33:04PM +0800, Zhenzhong Duan wrote:
> Driver init call graph under baremetal:
> driver_init->
> msix_capability_init->
> msix_program_entries->
> msix_mask_irq->
> entry->masked = 1
> request_irq->
> __setup_irq->
> irq_startup->
> unmask_msi_irq->
> msix_mask_irq->
> entry->masked = 0;
>
> So entry->masked is always updated with newest value and its value could be used
> to restore to mask register in device.
>
> But in initial domain (aka priviliged guest), it's different.
> Driver init call graph under initial domain:
> driver_init->
> msix_capability_init->
> msix_program_entries->
> msix_mask_irq->
> entry->masked = 1
> request_irq->
> __setup_irq->
> irq_startup->
> __startup_pirq->
> EVTCHNOP_bind_pirq hypercall (trap into Xen)
> [Xen:]
> pirq_guest_bind->
> startup_msi_irq->
> unmask_msi_irq->
> msi_set_mask_bit->
> entry->msi_attrib.masked = 0;
>
> So entry->msi_attrib.masked in xen side always has newest value. entry->masked
> in initial domain is untouched and is 1 after msix_capability_init.
If we run the following sequence:
pci_enable_msix()
request_irq()
don't we end up with the MSI IRQ unmasked if we're on bare metal but masked
if we're on Xen? It seems like we'd want it unmasked in both cases, so I
expected your patch to do something to make it unmasked if we're on Xen.
But I don't think it does, does it?
As far as I can tell, this patch only changes the pci_restore_state()
path. I think that part makes sense.
Bjorn
> Based on above, it's Xen's duty to restore entry->msi_attrib.masked to device,
> but with current code, entry->masked is used and MSI-x interrupt is masked.
>
> Before patch, restore call graph under initial domain:
> pci_reset_function->
> pci_restore_state->
> __pci_restore_msix_state->
> arch_restore_msi_irqs->
> xen_initdom_restore_msi_irqs->
> PHYSDEVOP_restore_msi hypercall (first mask restore)
> msix_mask_irq(entry, entry->masked) (second mask restore)
>
> So msix_mask_irq call in initial domain call graph needs to be removed.
>
> Based on this we can move the restore of the mask in default_restore_msi_irqs
> which would avoid restoring the invalid mask under Xen. Furthermore this
> simplifies the API by making everything related to restoring an MSI be in the
> platform specific APIs instead of just parts of it.
>
> After patch, restore call graph under initial domain:
> pci_reset_function->
> pci_restore_state->
> __pci_restore_msix_state->
> arch_restore_msi_irqs->
> xen_initdom_restore_msi_irqs->
> PHYSDEVOP_restore_msi hypercall (first mask restore)
>
> Logic for baremetal is not changed.
> Before patch, restore call graph under baremetal:
> pci_reset_function->
> pci_restore_state->
> __pci_restore_msix_state->
> arch_restore_msi_irqs->
> default_restore_msi_irqs->
> msix_mask_irq(entry, entry->masked) (first mask restore)
>
> After patch, restore call graph under baremetal:
> pci_reset_function->
> pci_restore_state->
> __pci_restore_msix_state->
> arch_restore_msi_irqs->
> default_restore_msi_irqs->
> msix_mask_irq(entry, entry->masked) (first mask restore)
>
> The process for MSI code is similiar.
>
> Tested-by: Sucheta Chakraborty <sucheta.chakraborty@...gic.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
> drivers/pci/msi.c | 17 ++++++++++++++---
> 1 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index ecd4cdf..38237f4 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -236,6 +236,8 @@ void unmask_msi_irq(struct irq_data *data)
>
> void default_restore_msi_irqs(struct pci_dev *dev, int irq)
> {
> + int pos;
> + u16 control;
> struct msi_desc *entry;
>
> entry = NULL;
> @@ -248,8 +250,19 @@ void default_restore_msi_irqs(struct pci_dev *dev, int irq)
> entry = irq_get_msi_desc(irq);
> }
>
> - if (entry)
> + if (entry) {
> write_msi_msg(irq, &entry->msg);
> + if (dev->msix_enabled) {
> + msix_mask_irq(entry, entry->masked);
> + readl(entry->mask_base);
> + } else {
> + pos = entry->msi_attrib.pos;
> + pci_read_config_word(dev, pos + PCI_MSI_FLAGS,
> + &control);
> + msi_mask_irq(entry, msi_capable_mask(control),
> + entry->masked);
> + }
> + }
> }
>
> void __read_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
> @@ -423,7 +436,6 @@ static void __pci_restore_msi_state(struct pci_dev *dev)
> arch_restore_msi_irqs(dev, dev->irq);
>
> pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
> - msi_mask_irq(entry, msi_capable_mask(control), entry->masked);
> control &= ~PCI_MSI_FLAGS_QSIZE;
> control |= (entry->msi_attrib.multiple << 4) | PCI_MSI_FLAGS_ENABLE;
> pci_write_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, control);
> @@ -447,7 +459,6 @@ static void __pci_restore_msix_state(struct pci_dev *dev)
>
> list_for_each_entry(entry, &dev->msi_list, list) {
> arch_restore_msi_irqs(dev, entry->irq);
> - msix_mask_irq(entry, entry->masked);
> }
>
> control &= ~PCI_MSIX_FLAGS_MASKALL;
> --
> 1.7.3
>
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