linux-kernel - Re: [PATCH V10 4/9] vfio: platform: add support for ACPI probe

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Message-ID: <20160718180049.78db3dfb@t450s.home>
Date:	Mon, 18 Jul 2016 18:00:49 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	kvm@...r.kernel.org, timur@...eaurora.org, cov@...eaurora.org,
	jcm@...hat.com, eric.auger@...hat.com, linux-acpi@...r.kernel.org,
	agross@...eaurora.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Baptiste Reynal <b.reynal@...tualopensystems.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V10 4/9] vfio: platform: add support for ACPI probe

On Mon, 18 Jul 2016 19:09:22 -0400
Sinan Kaya <okaya@...eaurora.org> wrote:

> The code is using the compatible DT string to associate a reset driver
> with the actual device itself. The compatible string does not exist on
> ACPI based systems. HID is the unique identifier for a device driver
> instead.
> 
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/vfio/platform/vfio_platform_common.c  | 69 +++++++++++++++++++++++++--
>  drivers/vfio/platform/vfio_platform_private.h |  1 +
>  2 files changed, 65 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index 6be92c3..a5299f6 100644
> --- a/drivers/vfio/platform/vfio_platform_common.c
> +++ b/drivers/vfio/platform/vfio_platform_common.c
> @@ -13,6 +13,7 @@
>   */
>  
>  #include <linux/device.h>
> +#include <linux/acpi.h>
>  #include <linux/iommu.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> @@ -49,6 +50,32 @@ static vfio_platform_reset_fn_t vfio_platform_lookup_reset(const char *compat,
>  	return reset_fn;
>  }
>  
> +static int vfio_platform_acpi_probe(struct vfio_platform_device *vdev,
> +				    struct device *dev)
> +{
> +	struct acpi_device *adev;
> +
> +	if (acpi_disabled)
> +		return -EPERM;
> +
> +	adev = ACPI_COMPANION(dev);

I didn't necessarily have a problem with this being set in the
declaration.

> +	if (!adev) {
> +		pr_err("VFIO: ACPI companion device not found for %s\n",
> +			vdev->name);
> +		return -ENODEV;
> +	}
> +
> +#ifdef CONFIG_ACPI
> +	vdev->acpihid = acpi_device_hid(adev);
> +	if (!vdev->acpihid) {
> +		pr_err("VFIO: cannot find ACPI HID for %s\n",
> +		       vdev->name);
> +		return -EINVAL;
> +	}
> +#endif
> +	return WARN_ON(!vdev->acpihid) ? -ENOENT : 0;

?!?!  The point was that that entire if{} branch is unnecessary.  The
WARN_ON handles the (impossible) case of !vdev->acpihid.  We just need:

#ifdef CONFIG_ACPI
	vdev->acpihid = acpi_device_hid(adev);
#endif
	return WARN_ON(!vdev->acpihid) ? -ENOENT : 0;

nit, might make sense to replace EPERM with ENOENT and use EINVAL here.

> +}
> +
>  static bool vfio_platform_has_reset(struct vfio_platform_device *vdev)
>  {
>  	return vdev->of_reset ? true : false;
> @@ -547,6 +574,37 @@ static const struct vfio_device_ops vfio_platform_ops = {
>  	.mmap		= vfio_platform_mmap,
>  };
>  
> +int vfio_platform_of_probe(struct vfio_platform_device *vdev,
> +			   struct device *dev)
> +{
> +	int ret;
> +
> +	ret = device_property_read_string(dev, "compatible",
> +					  &vdev->compat);
> +	if (ret)
> +		pr_err("VFIO: cannot retrieve compat for %s\n",
> +			vdev->name);
> +
> +	return ret;
> +}
> +
> +/*
> + * There can be two kernel build combinations. One build where
> + * ACPI is not selected in Kconfig and another one with the ACPI Kconfig.
> + *
> + * In the first case, vfio_platform_acpi_probe will return since
> + * acpi_disabled is 1. DT user will not see any kind of messages from
> + * ACPI.
> + *
> + * In the second case, both DT and ACPI is compiled in but the system is
> + * booting with any of these combinations.
> + *
> + * If the firmware is DT type, then acpi_disabled is 1. The ACPI probe routine
> + * terminates immediately without any messages.
> + *
> + * If the firmware is ACPI type, then acpi_disabled is 0. All other checks are
> + * valid checks. We cannot claim that this system is DT.
> + */
>  int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>  			       struct device *dev)
>  {
> @@ -556,11 +614,12 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>  	if (!vdev)
>  		return -EINVAL;
>  
> -	ret = device_property_read_string(dev, "compatible", &vdev->compat);
> -	if (ret) {
> -		pr_err("VFIO: cannot retrieve compat for %s\n", vdev->name);
> -		return -EINVAL;
> -	}
> +	ret = vfio_platform_acpi_probe(vdev, dev);
> +	if (ret)
> +		ret = vfio_platform_of_probe(vdev, dev);
> +
> +	if (ret)
> +		return ret;
>  
>  	vdev->device = dev;
>  
> diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
> index 71ed7d1..ba9e4f8 100644
> --- a/drivers/vfio/platform/vfio_platform_private.h
> +++ b/drivers/vfio/platform/vfio_platform_private.h
> @@ -58,6 +58,7 @@ struct vfio_platform_device {
>  	struct mutex			igate;
>  	struct module			*parent_module;
>  	const char			*compat;
> +	const char			*acpihid;
>  	struct module			*reset_module;
>  	struct device			*device;
>