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

Pierre Morel
2019-02-14T17:36:46Z

On 14/02/2019 17:57, Cornelia Huck wrote:
> 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?

...yes -(

> 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?)

On device_register there were no bus, so the core just do not look for a
driver and this field was nor tested nor overwritten.

>
>>
>>>
>>>>
>>>> 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.
>

:) definitively right
thanks, this will simplify the code in the next version.
I will take the patch away from this series to get the way to stable as
Christian requested.

Regards,
Pierre

--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany