Messages in this thread | | | Date | Thu, 17 Mar 2022 16:52:37 +0000 | Subject | Re: [PATCH 3/4 RESEND] Drivers: hv: vmbus: Propagate VMbus coherence to each VMbus device | From | Robin Murphy <> |
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On 2022-03-17 16:25, Michael Kelley via iommu wrote: > VMbus synthetic devices are not represented in the ACPI DSDT -- only > the top level VMbus device is represented. As a result, on ARM64 > coherence information in the _CCA method is not specified for > synthetic devices, so they default to not hardware coherent. > Drivers for some of these synthetic devices have been recently > updated to use the standard DMA APIs, and they are incurring extra > overhead of unneeded software coherence management. > > Fix this by propagating coherence information from the VMbus node > in ACPI to the individual synthetic devices. There's no effect on > x86/x64 where devices are always hardware coherent. > > Signed-off-by: Michael Kelley <mikelley@microsoft.com> > --- > drivers/hv/vmbus_drv.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > index 12a2b37..c0e993ad 100644 > --- a/drivers/hv/vmbus_drv.c > +++ b/drivers/hv/vmbus_drv.c > @@ -904,6 +904,21 @@ static int vmbus_probe(struct device *child_device) > drv_to_hv_drv(child_device->driver); > struct hv_device *dev = device_to_hv_device(child_device); > const struct hv_vmbus_device_id *dev_id; > + enum dev_dma_attr coherent; > + > + /* > + * On ARM64, propagate the DMA coherence setting from the top level > + * VMbus ACPI device to the child VMbus device being added here. > + * Older Hyper-V ARM64 versions don't set the _CCA method on the > + * top level VMbus ACPI device as they should. Treat these cases > + * as DMA coherent since that's the assumption made by Hyper-V. > + * > + * On x86/x64 these calls assume coherence and have no effect. > + */ > + coherent = acpi_get_dma_attr(hv_acpi_dev); > + if (coherent == DEV_DMA_NOT_SUPPORTED) > + coherent = DEV_DMA_COHERENT; > + acpi_dma_configure(child_device, coherent);
acpi_dma_configure is for devices represented in ACPI. The commit message implies that these VMBus devices aren't represented in ACPI. What gives?
Robin.
> > dev_id = hv_vmbus_get_id(drv, dev); > if (drv->probe) {
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