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

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Message-ID: <b4655a0ba9152e6b2951e379e1615dad@codeaurora.org>
Date:	Mon, 18 Jul 2016 20:16:50 -0400
From:	okaya@...eaurora.org
To:	Alex Williamson <alex.williamson@...hat.com>
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 2016-07-18 20:00, Alex Williamson wrote:
> 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.

I think this is better. If ACPI is disabled, it is dangerous to call an 
ACPI API.


> 
>> +	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;
> 

OK, got it now. I thought you were trying to get rid of #else

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

Sure, will take carr of it.

Anything else I need to take care of?

>> +}
>> +
>>  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;
>>