Re: [PATCH hyperv-next v5 09/11] Drivers: hv: vmbus: Introduce hv_get_vmbus_root_device()

[Roman Kisel <romank@linux.microsoft.com>]

On 3/10/2025 6:41 AM, Tianyu Lan wrote:
> On Sat, Mar 8, 2025 at 6:05 AM Roman Kisel <romank@linux.microsoft.com> wrote:
>>
>> The ARM64 PCI code for hyperv needs to know the VMBus root
>> device, and it is private.
>>
>> Provide a function that returns it. Rename it from "hv_dev"
>> as "hv_dev" as a symbol is very overloaded. No functional
>> changes.
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> 
> Why change all device's parent to vmbus_root_device?
> 

No changes from my account of the code. Please let me know if I am
misunderstanding the question.

> The ARM64 platform uses the device tree to enumerate vmbus
> devices..  Can we find the root device via device tree? vmbus
> code on the x86 use ACPI and it seems to work via ACPI.
> 
> 

Right, we find it from the DT as shown in the next patch:

+static struct irq_domain *hv_pci_of_irq_domain_parent(void)
+{
+	struct device_node *parent;
+	struct irq_domain *domain;
+
+	parent = of_irq_find_parent(hv_get_vmbus_root_device()->of_node);
+	domain = NULL;
+	if (parent) {
+		domain = irq_find_host(parent);
+		of_node_put(parent);
+	}
+
+	return domain;
+}
+

and later use it for `irq_create_hierarchy()`. Please let me know
if I missed anything in your question.

>> ---
>>   drivers/hv/vmbus_drv.c | 23 +++++++++++++++--------
>>   include/linux/hyperv.h |  2 ++
>>   2 files changed, 17 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
>> index c8474b48dcd2..7bfafe702963 100644
>> --- a/drivers/hv/vmbus_drv.c
>> +++ b/drivers/hv/vmbus_drv.c
>> @@ -45,7 +45,8 @@ struct vmbus_dynid {
>>          struct hv_vmbus_device_id id;
>>   };
>>
>> -static struct device  *hv_dev;
>> +/* VMBus Root Device */
>> +static struct device  *vmbus_root_device;
>>
>>   static int hyperv_cpuhp_online;
>>
>> @@ -80,9 +81,15 @@ static struct resource *fb_mmio;
>>   static struct resource *hyperv_mmio;
>>   static DEFINE_MUTEX(hyperv_mmio_lock);
>>
>> +struct device *hv_get_vmbus_root_device(void)
>> +{
>> +       return vmbus_root_device;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_get_vmbus_root_device);
>> +
>>   static int vmbus_exists(void)
>>   {
>> -       if (hv_dev == NULL)
>> +       if (vmbus_root_device == NULL)
>>                  return -ENODEV;
>>
>>          return 0;
>> @@ -861,7 +868,7 @@ static int vmbus_dma_configure(struct device *child_device)
>>           * On x86/x64 coherence is assumed and these calls have no effect.
>>           */
>>          hv_setup_dma_ops(child_device,
>> -               device_get_dma_attr(hv_dev) == DEV_DMA_COHERENT);
>> +               device_get_dma_attr(vmbus_root_device) == DEV_DMA_COHERENT);
>>          return 0;
>>   }
>>
>> @@ -1930,7 +1937,7 @@ int vmbus_device_register(struct hv_device *child_device_obj)
>>                       &child_device_obj->channel->offermsg.offer.if_instance);
>>
>>          child_device_obj->device.bus = &hv_bus;
>> -       child_device_obj->device.parent = hv_dev;
>> +       child_device_obj->device.parent = vmbus_root_device;
>>          child_device_obj->device.release = vmbus_device_release;
>>
>>          child_device_obj->device.dma_parms = &child_device_obj->dma_parms;
>> @@ -2292,7 +2299,7 @@ static int vmbus_acpi_add(struct platform_device *pdev)
>>          struct acpi_device *ancestor;
>>          struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
>>
>> -       hv_dev = &device->dev;
>> +       vmbus_root_device = &device->dev;
>>
>>          /*
>>           * Older versions of Hyper-V for ARM64 fail to include the _CCA
>> @@ -2383,7 +2390,7 @@ static int vmbus_device_add(struct platform_device *pdev)
>>          struct device_node *np = pdev->dev.of_node;
>>          int ret;
>>
>> -       hv_dev = &pdev->dev;
>> +       vmbus_root_device = &pdev->dev;
>>
>>          ret = of_range_parser_init(&parser, np);
>>          if (ret)
>> @@ -2702,7 +2709,7 @@ static int __init hv_acpi_init(void)
>>          if (ret)
>>                  return ret;
>>
>> -       if (!hv_dev) {
>> +       if (!vmbus_root_device) {
>>                  ret = -ENODEV;
>>                  goto cleanup;
>>          }
>> @@ -2733,7 +2740,7 @@ static int __init hv_acpi_init(void)
>>
>>   cleanup:
>>          platform_driver_unregister(&vmbus_platform_driver);
>> -       hv_dev = NULL;
>> +       vmbus_root_device = NULL;
>>          return ret;
>>   }
>>
>> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
>> index 7f4f8d8bdf43..1f0851fde041 100644
>> --- a/include/linux/hyperv.h
>> +++ b/include/linux/hyperv.h
>> @@ -1333,6 +1333,8 @@ static inline void *hv_get_drvdata(struct hv_device *dev)
>>          return dev_get_drvdata(&dev->device);
>>   }
>>
>> +struct device *hv_get_vmbus_root_device(void);
>> +
>>   struct hv_ring_buffer_debug_info {
>>          u32 current_interrupt_mask;
>>          u32 current_read_index;
>> --
>> 2.43.0
>>
>>
> 
> 

-- 
Thank you,
Roman