Subject: [PATCH v2 3/4] VFIO: platform: populate the reset function on probe

From: [email-masked] (Alex Williamson)
Date: Wed, 10 Jun 2015 09:10:53 -0600

On Wed, 2015-06-10 at 13:44 +0200, Eric Auger wrote:
> On 06/09/2015 08:26 PM, Alex Williamson wrote:
> > On Fri, 2015-06-05 at 17:06 +0200, Eric Auger wrote:
> >> The reset function lookup happens on vfio-platform probe. The reset
> >> module load is requested  and a reference to the function symbol is
> >> hold. The reference is released on vfio-platform remove.
> >>
> >> Signed-off-by: Eric Auger <[email-masked]>
> >>
> >> ---
> >>
> >> v1 -> v2:
> >> - [get,put]_reset now is called once on probe/remove
> >> - use request_module to automatically load the reset module that
> >>   matches the compatibility string
> >> - lookup table is used instead of list
> >> - remove registration mechanism: reset function name is stored in the
> >>   lookup table.
> >> - use device_property_read_string instead of
> >>   device_property_read_string_array
> >> ---
> >>  drivers/vfio/platform/vfio_platform_common.c | 48 +++++++++++++++++++++++++++-
> >>  1 file changed, 47 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> >> index 995929b..d474d6a 100644
> >> --- a/drivers/vfio/platform/vfio_platform_common.c
> >> +++ b/drivers/vfio/platform/vfio_platform_common.c
> >> @@ -31,6 +31,47 @@ static const struct vfio_platform_reset_combo reset_lookup_table[] = {
> >>  	},
> >>  };
> >>  
> >> +static int vfio_platform_get_reset(struct vfio_platform_device *vdev,
> >> +				   struct device *dev)
> >> +{
> >> +	const char *compat;
> >> +	const struct vfio_platform_reset_combo *iter = reset_lookup_table;
> >> +	int (*reset)(struct vfio_platform_device *);
> >> +	int ret;
> >> +
> >> +	vdev->type = VFIO_PLATFORM_RESET_TYPE_MAX;
> >> +	ret = device_property_read_string(dev, "compatible", &compat);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	while (iter->type < VFIO_PLATFORM_RESET_TYPE_MAX) {
> >> +		if (!strcmp(iter->compat, compat)) {
> >> +			request_module(iter->module_name);
> >> +			reset = __symbol_get(iter->reset_function_name);
> > 
> > symbol_get() appears to be the more robust and dominant interface for
> > this, why use __symbol_get()? 
> I used this because it takes a const char * as an argument and this is
> what I use as a datatype for storing the reset function name. Symbol_get
> is provided with the symbol directly? It is also used
> drivers/mtd/chips/gen_probe.c.

But symbol_get() is just some macro wrappers around __symbol_get() that
handles tool chains that precede symbols with underscores.  I don't
really know if that's still a concern, but are you sure it doesn't work?

> > 
> >> +			if (reset) {
> >> +				vdev->type = iter->type;
> >> +				vdev->reset = reset;
> >> +				return 0;
> >> +			}
> >> +		}
> >> +		iter++;
> >> +	}
> >> +	return -1;
> > 
> > -ENODEV seems preferable to -1, but shouldn't this really be a void
> > function?
> yes indeed
> > 
> >> +}
> >> +
> >> +static void vfio_platform_put_reset(struct vfio_platform_device *vdev)
> >> +{
> >> +	const struct vfio_platform_reset_combo *iter = reset_lookup_table;
> >> +
> >> +	while (iter->type < VFIO_PLATFORM_RESET_TYPE_MAX) {
> >> +		if (iter->type == vdev->type) {
> > 
> > Again, I don't see the value in storing the enum, since the table is
> > static, it could just as easily be the array index and avoid this loop,
> > but we can avoid it anyway with symbol_put_addr().
> yes you're definitively right!
> 
> Thanks
> 
> Eric
> > 
> >> +			__symbol_put(iter->reset_function_name);
> >> +			return;
> >> +		}
> >> +		iter++;
> >> +	}
> >> +}
> >> +
> >>  static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
> >>  {
> >>  	int cnt = 0, i;
> >> @@ -519,6 +560,8 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
> >>  		return ret;
> >>  	}
> >>  
> >> +	vfio_platform_get_reset(vdev, dev);
> >> +
> >>  	mutex_init(&vdev->igate);
> >>  
> >>  	return 0;
> >> @@ -530,8 +573,11 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
> >>  	struct vfio_platform_device *vdev;
> >>  
> >>  	vdev = vfio_del_group_dev(dev);
> >> -	if (vdev)
> >> +
> >> +	if (vdev) {
> >> +		vfio_platform_put_reset(vdev);
> >>  		iommu_group_put(dev->iommu_group);
> >> +	}
> >>  
> >>  	return vdev;
> >>  }
> > 
> > 
> > 
> > 
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> > 
>