Re: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the "ap" parent bus

[Tony Krowiak]

On 1/27/22 05:33, Thomas Huth wrote:
> On 14/12/2021 22.28, Tony Krowiak wrote:
> > On 12/13/21 10:44, Harald Freudenberger wrote:
> > > On 01.12.21 15:11, Thomas Huth wrote:
> > > > The crypto devices that we can use with the vfio_ap module are sitting
> > > > on the "ap" bus, not on the "vfio_ap" bus that the module defines
> > > > itself. With this change, the vfio_ap module now gets automatically
> > > > loaded if a supported crypto adapter is available in the host.
> > > >
> > > > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> > > > ---
> > > >   Note: Marked as "RFC" since I'm not 100% sure about it ...
> > > >         please review carefully!
> > > >
> > > >   drivers/s390/crypto/vfio_ap_drv.c | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/s390/crypto/vfio_ap_drv.c 
> > > > b/drivers/s390/crypto/vfio_ap_drv.c
> > > > index 4d2556bc7fe5..5580e40608a4 100644
> > > > --- a/drivers/s390/crypto/vfio_ap_drv.c
> > > > +++ b/drivers/s390/crypto/vfio_ap_drv.c
> > > > @@ -39,7 +39,7 @@ static struct ap_device_id ap_queue_ids[] = {
> > > >       { /* end of sibling */ },
> > > >   };
> > > > -MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
> > > > +MODULE_DEVICE_TABLE(ap, ap_queue_ids);
> > > >   /**
> > > >    * vfio_ap_queue_dev_probe:
> > > I had a chance to check this now.
> > > First I have to apologize about the dispute with vfio devices 
> > > appearing on the ap bus.
> > > That's not the case with this patch. As Connie states the 
> > > MODULE_DEVICE_TABLE() does not
> > > change the parent of a device and vfio_ap_drv is a driver for ap 
> > > devices and thus
> > > belongs to the ap bus anyway.
> > > So what's left is that with this change the vfio_ap kernel module is 
> > > automatically loaded
> > > when an ap device type 10-13 is recognized by the ap bus. So the 
> > > intention of the patch
> > > is fulfilled.
> > > Yet another kernel module which may occupy memory but will never get 
> > > used by most customers.
> > > This may not be a problem but I had a glance at the list of kernel 
> > > modules loaded on my
> > > LPAR with and without the patch and the difference is:
> > > ...
> > > kvm                   512000  1 vfio_ap
> > > vfio_ap                28672  0
> > > ...
> > > So the vfio_ap module has a dependency to the biggest kernel module 
> > > ever - kvm.
> > > Do I need to say something more?
> > >
> > > If this dependency is removed then I would not hesitate to accept 
> > > this patch. However
> > > this is up to Tony as he is the maintainer of the vfio ap device 
> > > driver.
> >
> > The vfio_ap device driver has a dependency on kvm, it can not be 
> > removed.
> > If the user base for vfio_ap is minimal, then I see no reason why the 
> > vfio_ap
> > module should be automatically loaded when an AP device type 10-13 is
> > recognized by the AP bus. The module is needed only to pass through AP
> > queue devices to a KVM guest.
>
> To continue the discussion here - it seems like my patch here won't be 
> accepted? Shall I send another one instead to remove the bad 
> MODLE_DEVICE_TABLE from the vfio_ap_drv.c file?
>
>  Thomas

After re-reviewing all of the comments, I am okay with this patch:

Reviewed-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>

If there are any other objections, speak now or forever hold your peace:)