linux-kernel - Re: [PATCH V8 4/9] vfio: platform: add support for ACPI probe

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Message-ID: <20160623123410.647b3be0@t450s.home>
Date:	Thu, 23 Jun 2016 12:34:10 -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 V8 4/9] vfio: platform: add support for ACPI probe

On Mon, 20 Jun 2016 11:51:14 -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>
> Reviewed-by: Eric Auger <eric.auger@...hat.com>
> Reviewed-by: Baptiste Reynal <b.reynal@...tualopensystems.com>
> ---
>  drivers/vfio/platform/vfio_platform_common.c  | 57 ++++++++++++++++++++++++---
>  drivers/vfio/platform/vfio_platform_private.h |  1 +
>  2 files changed, 53 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index 6be92c3..fbf4565 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 +50,37 @@ static vfio_platform_reset_fn_t vfio_platform_lookup_reset(const char *compat,
>  	return reset_fn;
>  }
>  
> +#ifdef CONFIG_ACPI
> +static int vfio_platform_acpi_probe(struct vfio_platform_device *vdev,
> +				    struct device *dev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(dev);
> +
> +	if (acpi_disabled)
> +		return -ENODEV;
> +
> +	if (!adev) {
> +		pr_err("VFIO: ACPI companion device not found for %s\n",
> +			vdev->name);
> +		return -ENODEV;
> +	}
> +
> +	vdev->acpihid = acpi_device_hid(adev);
> +	if (!vdev->acpihid) {
> +		pr_err("VFIO: cannot find ACPI HID for %s\n",
> +		       vdev->name);
> +		return -ENODEV;
> +	}

Do you want to try to use different errnos here so you don't rely on
the pr_err() calls for debugging?  I could imagine -EPERM, -ENODEV,
-EINVAL respectively, but maybe there are better options.

> +	return 0;
> +}
> +#else
> +static inline int vfio_platform_acpi_probe(struct vfio_platform_device *vdev,
> +					   struct device *dev)
> +{
> +	return -ENOENT;
> +}
> +#endif
> +
>  static bool vfio_platform_has_reset(struct vfio_platform_device *vdev)
>  {
>  	return vdev->of_reset ? true : false;
> @@ -547,6 +579,20 @@ 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);

Previously there was only one probe method and I imagine this pr_err
was useful.  Now we have multiple methods of probing for the device.
Do we really want each one generating pr_err messages or just one at
the end if none of our probes worked?

> +
> +	return ret;
> +}
> +
>  int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>  			       struct device *dev)
>  {
> @@ -556,11 +602,12 @@ 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);


The only out way out of vfio_platform_acpi_probe() without hitting a
pr_err is one of (!CONFIG_ACPI || acpi_disabled || success).  Doesn't
that make for some unnecessary warning for a DT user?


> +
> +	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;
>