Re: [PATCH v7 3/3] virt: vmgenid: add support for devicetree bindings

["Landge, Sudan" <sudanl@amazon.co.uk>]

On 18/04/2024 13:12, Jason A. Donenfeld wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> From: Sudan Landge <sudanl@amazon.com>
> 
> Extend the vmgenid platform driver to support devicetree bindings. With
> this support, hypervisors can send vmgenid notifications to the virtual
> machine without the need to enable ACPI. The bindings are located at:
> Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml
> 
> Since this makes the driver work for both ACPI and devicetree, adjust
> the Kconfig to include `|| OF`, which in turn means accounting for
> !CONFIG_ACPI in the code with a short ifdef.
> 
> Signed-off-by: Sudan Landge <sudanl@amazon.com>
> Reviewed-by: Alexander Graf <graf@amazon.com>
> [Jason: - Small style cleanups and refactoring.
>          - Fold in Kconfig OF dependency and ACPI conditionalization. ]
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>   drivers/virt/Kconfig   |  2 +-
>   drivers/virt/vmgenid.c | 53 ++++++++++++++++++++++++++++++++++++++++--
>   2 files changed, 52 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
> index 40129b6f0eca..017d6c38c3ba 100644
> --- a/drivers/virt/Kconfig
> +++ b/drivers/virt/Kconfig
> @@ -16,7 +16,7 @@ if VIRT_DRIVERS
>   config VMGENID
>          tristate "Virtual Machine Generation ID driver"
>          default y
> -       depends on ACPI
> +       depends on ACPI || OF

Version 2 of the patches had these flag but were removed in version3 
following the below review comment from Rob:
"One of those is pretty much always enabled, so it can probably be dropped."
reference : 
https://lore.kernel.org/lkml/CAL_JsqJoB5CYajWuntMdQrJZir+ZA-69Q0cwvxcVZAqs-mXC+Q@mail.gmail.com/


>          help
>            Say Y here to use the hypervisor-provided Virtual Machine Generation ID
>            to reseed the RNG when the VM is cloned. This is highly recommended if
> diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
> index aebbd24512c9..7f2d1e5656df 100644
> --- a/drivers/virt/vmgenid.c
> +++ b/drivers/virt/vmgenid.c
> @@ -2,12 +2,13 @@
>   /*
>    * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
>    *
> - * The "Virtual Machine Generation ID" is exposed via ACPI and changes when a
> + * The "Virtual Machine Generation ID" is exposed via ACPI or DT and changes when a
>    * virtual machine forks or is cloned. This driver exists for shepherding that
>    * information to random.c.
>    */
> 
>   #include <linux/acpi.h>
> +#include <linux/interrupt.h>
>   #include <linux/kernel.h>
>   #include <linux/module.h>
>   #include <linux/platform_device.h>
> @@ -41,6 +42,7 @@ static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
>          add_device_randomness(state->this_id, sizeof(state->this_id));
>   }
> 
> +#ifdef CONFIG_ACPI
>   static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
>                                   u32 __always_unused event, void *dev)
>   {
> @@ -92,6 +94,43 @@ static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
>          ACPI_FREE(parsed.pointer);
>          return ret;
>   }
> +#else
> +static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
> +{
> +       return -EINVAL;
> +}
> +#endif
> +
> +static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev)
> +{
> +       vmgenid_notify(dev);
> +       return IRQ_HANDLED;
> +}
> +
> +static int vmgenid_add_of(struct platform_device *pdev,
> +                         struct vmgenid_state *state)
> +{
> +       void *virt_addr;
> +       int ret;
> +
> +       virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
> +       if (IS_ERR(virt_addr))
> +               return PTR_ERR(virt_addr);
> +
> +       setup_vmgenid_state(state, virt_addr);
> +
> +       ret = platform_get_irq(pdev, 0);
> +       if (ret)
> +               return ret;
> +
> +       ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler,
> +                              IRQF_SHARED, "vmgenid", &pdev->dev);
> +       if (ret)
> +               return ret;
> +
> +       pdev->dev.driver_data = state;
> +       return 0;
> +}
> 
>   static int vmgenid_add(struct platform_device *pdev)
>   {
> @@ -103,13 +142,22 @@ static int vmgenid_add(struct platform_device *pdev)
>          if (!state)
>                  return -ENOMEM;
> 
> -       ret = vmgenid_add_acpi(dev, state);
> +       if (dev->of_node)
> +               ret = vmgenid_add_of(pdev, state);
> +       else
> +               ret = vmgenid_add_acpi(dev, state);
> 
>          if (ret)
>                  devm_kfree(dev, state);
>          return ret;
>   }
> 
> +static const struct of_device_id vmgenid_of_ids[] = {
> +       { .compatible = "microsoft,vmgenid", },
> +       { },
> +};
> +MODULE_DEVICE_TABLE(of, vmgenid_of_ids);
> +
>   static const struct acpi_device_id vmgenid_acpi_ids[] = {
>          { "VMGENCTR", 0 },
>          { "VM_GEN_COUNTER", 0 },
> @@ -122,6 +170,7 @@ static struct platform_driver vmgenid_plaform_driver = {
>          .driver     = {
>                  .name   = "vmgenid",
>                  .acpi_match_table = vmgenid_acpi_ids,
> +               .of_match_table = vmgenid_of_ids,
>          },
>   };
> 
> --
> 2.44.0
> 
Since I am on leave, looping in Babis to review/verify the patches.