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Message-ID: <dc7db611-c4f7-412d-8ace-f675a068f966@linux.microsoft.com>
Date: Wed, 15 May 2024 11:21:46 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>, "arnd@...db.de" <arnd@...db.de>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>, "bp@...en8.de" <bp@...en8.de>,
"catalin.marinas@....com" <catalin.marinas@....com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"decui@...rosoft.com" <decui@...rosoft.com>,
"haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
"hpa@...or.com" <hpa@...or.com>, "kw@...ux.com" <kw@...ux.com>,
"kys@...rosoft.com" <kys@...rosoft.com>, "lenb@...nel.org"
<lenb@...nel.org>, "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
"mingo@...hat.com" <mingo@...hat.com>, "rafael@...nel.org"
<rafael@...nel.org>, "robh@...nel.org" <robh@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"wei.liu@...nel.org" <wei.liu@...nel.org>, "will@...nel.org"
<will@...nel.org>, "linux-acpi@...r.kernel.org"
<linux-acpi@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>
Cc: "ssengar@...rosoft.com" <ssengar@...rosoft.com>,
"sunilmut@...rosoft.com" <sunilmut@...rosoft.com>,
"vdso@...bites.dev" <vdso@...bites.dev>
Subject: Re: [PATCH v2 5/6] drivers/hv/vmbus: Get the irq number from
DeviceTree
On 5/15/2024 6:44 AM, Michael Kelley wrote:
> From: Roman Kisel <romank@...ux.microsoft.com> Sent: Tuesday, May 14, 2024 3:44 PM
>>
>> The vmbus driver uses ACPI for interrupt assignment on
>> arm64 hence it won't function in the VTL mode where only
>> DeviceTree can be used.
>>
>> Update the vmbus driver to discover interrupt configuration
>> via DeviceTree.
>>
>> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
>> ---
>> drivers/hv/vmbus_drv.c | 37 +++++++++++++++++++++++++++++++++++++
>> 1 file changed, 37 insertions(+)
>>
>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
>> index e25223cee3ab..52f01bd1c947 100644
>> --- a/drivers/hv/vmbus_drv.c
>> +++ b/drivers/hv/vmbus_drv.c
>> @@ -36,6 +36,7 @@
>> #include <linux/syscore_ops.h>
>> #include <linux/dma-map-ops.h>
>> #include <linux/pci.h>
>> +#include <linux/of_irq.h>
>> #include <clocksource/hyperv_timer.h>
>> #include <asm/mshyperv.h>
>> #include "hyperv_vmbus.h"
>> @@ -2316,6 +2317,34 @@ static int vmbus_acpi_add(struct platform_device *pdev)
>> }
>> #endif
>>
>> +static int __maybe_unused vmbus_of_set_irq(struct device_node *np)
>> +{
>> + struct irq_desc *desc;
>> + int irq;
>> +
>> + irq = of_irq_get(np, 0);
>> + if (irq == 0) {
>> + pr_err("VMBus interrupt mapping failure\n");
>> + return -EINVAL;
>> + }
>> + if (irq < 0) {
>> + pr_err("VMBus interrupt data can't be read from DeviceTree, error %d\n", irq);
>> + return irq;
>> + }
>> +
>> + desc = irq_to_desc(irq);
>> + if (!desc) {
>> + pr_err("VMBus interrupt description can't be found for virq %d\n", irq);
>
> s/description/descriptor/
>
> Or maybe slightly more compact overall: "No interrupt descriptor for VMBus virq %d\n".
>
Yep, thanks!
>> + return -ENODEV;
>> + }
>> +
>> + vmbus_irq = irq;
>> + vmbus_interrupt = desc->irq_data.hwirq;
>> + pr_debug("VMBus virq %d, hwirq %d\n", vmbus_irq, vmbus_interrupt);
>
> How does device DMA cache coherency get handled in the DeviceTree case on
> arm64? For vmbus_acpi_add(), there's code to look at the _CCA flag, which is
> required in ACPI for arm64. (There's also code to handle the Hyper-V bug where
> _CCA is omitted.) I don't know DeviceTree, but is there a similar flag to indicate
> device cache coherency? Of course, Hyper-V always assumes DMA cache
> coherency, and that's a valid assumption for the server-class systems that
> would run Hyper-V VMs on arm64. But the Linux DMA subsystem needs to be
> told, and vmbus_dma_configure() needs to propagate the setting from the
> VMBus device to the child VMBus devices. Everything still works if the Linux
> DMA subsystem isn't told, but you end up with a perf hit. The DMA code
> defaults to "not coherent" on arm64, and you'll get a lot of high-cost cache
> coherency maintenance done by the CPU when it is unnecessary. This issue
> doesn't arise on x86 since the architecture requires DMA cache coherency, and
> the Linux default is "coherent".
>
Appreciate the indispensable insight! I'll straighten this out.
>> +
>> + return 0;
>> +}
>> +
>> static int vmbus_device_add(struct platform_device *pdev)
>> {
>> struct resource **cur_res = &hyperv_mmio;
>> @@ -2324,12 +2353,20 @@ static int vmbus_device_add(struct platform_device *pdev)
>> struct device_node *np = pdev->dev.of_node;
>> int ret;
>>
>> + pr_debug("VMBus is present in DeviceTree\n");
>> +
>
> I'm not clear on how interpret this debug message. Reaching this point in the code
> path just means that acpi_disabled is "true". DeviceTree hasn't yet been searched to
> see if VMBus is found.
>
True. Will remove.
>> hv_dev = &pdev->dev;
>>
>> ret = of_range_parser_init(&parser, np);
>> if (ret)
>> return ret;
>>
>> +#ifndef HYPERVISOR_CALLBACK_VECTOR
>> + ret = vmbus_of_set_irq(np);
>> + if (ret)
>> + return ret;
>> +#endif
>> +
>> for_each_of_range(&parser, &range) {
>> struct resource *res;
>>
>> --
>> 2.45.0
>>
>
--
Thank you,
Roman
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