Messages in this thread Patch in this message |  | | Date | Fri, 12 Jan 2024 15:16:45 -0800 | | From | Dan Williams <> | | Subject | RE: [PATCH] cxl/pci: Skip irq features if MSI/MSI-X are not supported |
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Ira Weiny wrote: > CXL 3.1 Section 3.1.1 states: > > "A Function on a CXL device must not generate INTx messages if > that Function participates in CXL.cache protocol or CXL.mem > protocols." > > The generic CXL memory driver only supports devices which use the > CXL.mem protocol. The current driver attempts to allocate MSI/MSI-X > vectors in anticipation of their need for mailbox interrupts or event > processing. However, the above requirement does not require a device to > support interrupts, only that they use MSI/MSI-X. For example, a device > may disable mailbox interrupts and be configured for firmware first > event processing and function well with the driver. > > Rather than fail device probe if interrupts are not supported; flag that > irqs are not enabled and avoid features which require interrupts. > Emit messages appropriate for the situation to aid in debugging should > device behavior be unexpected due to a failure to allocate vectors. > > Note that it is possible for a device to have host based event > processing through polling. However, the driver does not support > polling and it is not anticipated to be required. Leave that case to > the future if such a device comes along. > > Signed-off-by: Ira Weiny <ira.weiny@intel.com> > --- > Changes in v1: > - [djbw: remove persistent irq boolean] > - [djbw: Simplify error messages] > - [Alison: spell check] > - [iweiny: test] > - Link to RFC: https://lore.kernel.org/r/20240108-dont-fail-irq-v1-1-4407228debd2@intel.com > --- > drivers/cxl/pci.c | 29 +++++++++++++++++++---------- > 1 file changed, 19 insertions(+), 10 deletions(-) > > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c > index 0155fb66b580..bd12b97bb38e 100644 > --- a/drivers/cxl/pci.c > +++ b/drivers/cxl/pci.c > @@ -381,7 +381,7 @@ static int cxl_pci_mbox_send(struct cxl_memdev_state *mds, > return rc; > } > > -static int cxl_pci_setup_mailbox(struct cxl_memdev_state *mds) > +static int cxl_pci_setup_mailbox(struct cxl_memdev_state *mds, bool irq_avail) > { > struct cxl_dev_state *cxlds = &mds->cxlds; > const int cap = readl(cxlds->regs.mbox + CXLDEV_MBOX_CAPS_OFFSET); > @@ -443,6 +443,11 @@ static int cxl_pci_setup_mailbox(struct cxl_memdev_state *mds) > if (!(cap & CXLDEV_MBOX_CAP_BG_CMD_IRQ)) > return 0; > > + if (!irq_avail) { > + dev_err(cxlds->dev, "Mailbox irq enabled but no interrupt vectors.\n"); > + return 0; > + }
It is just odd for this to be dev_err() when the very next thing this function does is:
irq = pci_irq_vector(to_pci_dev(cxlds->dev), msgnum); if (irq < 0) return 0;
..which is silently return if using the interrupt does not work, or there is a problem with the device where it returns an invalid @msgnum. Why does one device "bug" deserve a dev_err() callout and the other doesn't?
So at a minimum the dev_err() should be a dev_dbg(), but I would just fold the @irq_avail check with the @cap check and be silent, because nobody will care that this device is not sending mailbox interrupts polling will just work.
> + > msgnum = FIELD_GET(CXLDEV_MBOX_CAP_IRQ_MSGNUM_MASK, cap); > irq = pci_irq_vector(to_pci_dev(cxlds->dev), msgnum); > if (irq < 0) > @@ -587,7 +592,7 @@ static int cxl_mem_alloc_event_buf(struct cxl_memdev_state *mds) > return devm_add_action_or_reset(mds->cxlds.dev, free_event_buf, buf); > } > > -static int cxl_alloc_irq_vectors(struct pci_dev *pdev) > +static bool cxl_alloc_irq_vectors(struct pci_dev *pdev) > { > int nvecs; > > @@ -604,9 +609,9 @@ static int cxl_alloc_irq_vectors(struct pci_dev *pdev) > PCI_IRQ_MSIX | PCI_IRQ_MSI); > if (nvecs < 1) { > dev_dbg(&pdev->dev, "Failed to alloc irq vectors: %d\n", nvecs); > - return -ENXIO; > + return false; > } > - return 0; > + return true; > } > > static irqreturn_t cxl_event_thread(int irq, void *id) > @@ -742,7 +747,7 @@ static bool cxl_event_int_is_fw(u8 setting) > } > > static int cxl_event_config(struct pci_host_bridge *host_bridge, > - struct cxl_memdev_state *mds) > + struct cxl_memdev_state *mds, bool irq_avail) > { > struct cxl_event_interrupt_policy policy; > int rc; > @@ -754,6 +759,11 @@ static int cxl_event_config(struct pci_host_bridge *host_bridge, > if (!host_bridge->native_cxl_error) > return 0; > > + if (!irq_avail) { > + dev_info(mds->cxlds.dev, "No interrupt vectors, no polling, skip event processing.\n");
Not going to demand dev_dbg() here just because a device is mandated to have event command support and it is driver policy to skip enabling it. However, do drop the "no polling" that's implied. So I think it is:
"No interrupt support, disable event processing."
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