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    SubjectRe: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the "ap" parent bus
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    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@redhat.com>
    >> ---
    >> 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.

    Since the vfio_ccw module also needs the kvm module and is automatically
    loaded,
    I see no problem with automatically loading the vfio_ap module. I tested
    this patch by
    running all of my regression tests successfully.

    >
    >

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