Re: [PATCH v3 1/9] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem

Cornelia Huck
2019-02-14T16:57:30Z

On Thu, 14 Feb 2019 16:47:30 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> On 14/02/2019 15:54, Cornelia Huck wrote:
> > On Thu, 14 Feb 2019 14:51:01 +0100
> > Pierre Morel <pmorel@linux.ibm.com> wrote:

> >> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> >> @@ -24,8 +24,9 @@ MODULE_LICENSE("GPL v2");
> >>
> >> static struct ap_driver vfio_ap_drv;
> >>
> >> -static struct device_type vfio_ap_dev_type = {
> >> - .name = VFIO_AP_DEV_TYPE_NAME,
> >> +struct matrix_driver {
> >> + struct device_driver drv;
> >> + int device_count;
> >
> > This counter basically ensures that at most one device may bind with
> > this driver... you'd still have that device on the bus, though.
>
> yes, this is what is wanted: this driver can only support one device.
> May be another matrix driver can support one or more other devices.
>
> I should update comment message my be.
>
> >
> >> };
> >>
> >> struct ap_matrix_dev *matrix_dev;
>
> >>
> >> - matrix_dev->device.type = &vfio_ap_dev_type;
> >> dev_set_name(&matrix_dev->device, "%s", VFIO_AP_DEV_NAME);
> >> matrix_dev->device.parent = root_device;
> >> + matrix_dev->device.bus = &matrix_bus;
> >> matrix_dev->device.release = vfio_ap_matrix_dev_release;
> >> - matrix_dev->device.driver = &vfio_ap_drv.driver;
> >> + matrix_dev->vfio_ap_drv = &vfio_ap_drv;
> >
> > Can't you get that structure through matrix_dev->device.driver instead
> > when you need it in the function below?
>
> Not anymore.
> We have two different drivers and devices
> matrix_drv <-> matrix_dev
> and
> vfio_ap_drv <-> ap_devices
>
> The driver behind the matrix_dev->dev->driver is matrix_drv
> what is needed here is vfio_ap_drv.

Wait, we had tacked a driver for ap devices unto a matrix device, which
is not on the ap bus? Maybe that's what trips libudev?

(And reading further in the current code, it seems we clear that
structure _after_ the matrix device had been setup, so how can that
even work? Where am I confused?)

>
> >
> >>
> >> ret = device_register(&matrix_dev->device);
> >> if (ret)
> >> goto matrix_reg_err;
> >>
> >> + ret = driver_register(&matrix_driver.drv);
> >> + if (ret)
> >> + goto matrix_drv_err;
> >> +
> >
> > As you already have several structures that can be registered exactly
> > once (the root device, the bus, the driver, ...), you can already be
> > sure that there's only one device on the bus, can't you?
>
> hum, no I don't think so, no device can register before this module is
> loaded, but what does prevent a device to register later from another
> module?

Not unless you export the interface, I guess.