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

[Alex Williamson]

On Wed, 13 Jul 2016 15:36:48 -0400
Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:

> Hi Alex,
> 
> On 6/23/2016 2:34 PM, Alex Williamson wrote:
> > On Mon, 20 Jun 2016 11:51:14 -0400
> > Sinan Kaya <okaya@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> >> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
> >> Reviewed-by: Baptiste Reynal <b.reynal@xxxxxxxxxxxxxxxxxxxxxx>
> >> ---
> >>  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.
> >   
> 
> will do.
> 
> >> +	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?  
> 
> IMO, the new approach is better and is more specific. The error messages
> are firmware specific. The previous message included missing compat string
> for instance doesn't exist on ACPI firmware and ACPI HID also doesn't exist
> on DT firmware. 
> 
> I'd rather be verbose rather than a simple probe failed message.
> 
> >   
> >> +
> >> +	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?  
> 
> Let me explain the rationale.
> 
> As you know, 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, CONFIG_ACPI is stubbed out in this file and 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.


Thanks, this sort of information and assumption should be documented in
a comment since not all of us care whether a DT device can appear in an
ACPI config or not.  Also note that acpi_disabled and ACPI_COMPANION
are defined regardless of CONFIG_ACPI, so really we only need to wrap
acpi_device_hid() in an #ifdef, we could skip the separate stub.
Thanks,

Alex


> > 
> >   
> >> +
> >> +	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;
> >>    
> >   
> 
>