From: Dave Jiang <dave.jiang@intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>,
Alex Williamson <alex.williamson@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
kvm@vger.kernel.org, Kirti Wankhede <kwankhede@nvidia.com>,
"Raj, Ashok" <ashok.raj@intel.com>,
Daniel Vetter <daniel@ffwll.ch>,
Leon Romanovsky <leonro@nvidia.com>,
Max Gurtovoy <mgurtovoy@nvidia.com>,
Tarun Gupta <targupta@nvidia.com>
Subject: Re: [PATCH v2 02/13] vfio/mdev: Allow the mdev_parent_ops to specify the device driver to bind
Date: Wed, 28 Apr 2021 17:00:17 -0700 [thread overview]
Message-ID: <bda5a770-9c0d-9a52-e8f5-78f07c3e7ef1@intel.com> (raw)
In-Reply-To: <20210428233856.GY1370958@nvidia.com>
On 4/28/2021 4:38 PM, Jason Gunthorpe wrote:
> On Wed, Apr 28, 2021 at 12:58:29PM -0700, Dan Williams wrote:
>> On Wed, Apr 28, 2021 at 7:00 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>>> On Wed, Apr 28, 2021 at 02:41:53PM +0200, Christoph Hellwig wrote:
>>>> On Wed, Apr 28, 2021 at 12:56:21AM -0700, Dan Williams wrote:
>>>>>> I still think this going the wrong way. Why can't we enhance the core
>>>>>> driver code with a version of device_bind_driver() that does call into
>>>>>> ->probe? That probably seems like a better model for those existing
>>>>>> direct users of device_bind_driver or device_attach with a pre-set
>>>>>> ->drv anyway.
>>>>> Wouldn't that just be "export device_driver_attach()" so that drivers
>>>>> can implement their own custom bind implementation?
>>>> That looks like it might be all that is needed.
>>> I thought about doing it like that, it is generally a good idea,
>>> however, if I add new API surface to the driver core I really want to
>>> get rid of device_bind_driver(), or at least most of its users.
>> I might be missing where you are going with this comment, but
>> device_driver_attach() isn't a drop-in replacement for
>> device_bind_driver().
> Many of the places calling device_bind_driver() are wonky things
> like this:
>
> dev->dev.driver = &drv->link.driver;
> if (pnp_bus_type.probe(&dev->dev))
> goto err_out;
> if (device_bind_driver(&dev->dev))
> goto err_out;
>
> So device_driver_attach() does replace that - with some differences.
>
> Notable is that bind_driver requires the driver_lock but driver_attach
> gets it internally. However, as far as I can tell, none of the
> bind_driver callers do get it, so huh.
>
> Aside from the driver_lock there are lots of small subtle differences
> that are probably not important unless they are for some very complex
> reason. :\
>
> Of the callers:
> drivers/input/serio/serio.c
> This definitely doesn't have the device_lock
> It uses connect instead of probe and for some reason uses its own
> mutex instead of the device_lock. Murky.
>
> drivers/input/gameport/gameport.c
> This looks alot like serio, same comments
>
> drivers/net/phy/phy_device.c
> device_driver_attach() is better, looks unlikely that
> device_lock is properly held here. Little unclear on what
> the bus is and if bus->probe will be OK
>
> drivers/net/wireless/mac80211_hwsim.c
> Definitely does not hold the driver lock, the class and the driver
> have NULL probes so this could be changed
>
> drivers/pnp/card.c
> device_driver_attach() is better, very unlikely that a random
> device pulled from a linked list has the driver_lock held
>
> drivers/usb/core/driver.c
> This comment says the caller must have the device lock, but it
> doesn't call probe, and when I look at cdc_ether.c I wonder
> where the device_lock is hidden? Murky.
>
> Basically, there is some mess here, and eliminating
> device_bind_driver() for device_driver_attach() is quite a reasonable
> cleanup. But hard, complex enough it needs testing each patch.
>
> The other driver self bind scenario is to directly assign driver
> before device_add, but I have a hard time finding those cases in the
> tree with grep.
>
>> If this export prevented a new device_bind_driver() user, I think
>> that's a net positive, because device_bind_driver() seems an odd way
>> to implement bus code to me.
> Yes, I looked into why it is like this and concluded it is just very
> very old.
>
>> I have an ulterior motive / additional use case in mind here which is
>> the work-in-progress cleanup of the DSA driver. It uses the driver
>> model to assign an engine to different use cases via driver binding.
>> However, it currently has a custom bind implementation that does not
>> operate like a typical /sys/bus/$bus/drivers interface. If
>> device_driver_attach() was exported then some DSA compat code could
>> model the current way while also allowing a transition path to the
>> right way. As is I was telling Dave that the compat code would need to
>> be built-in because I don't think fixing a DSA device-model problem is
>> enough justification on its own to ask for a device_driver_attach()
>> export.
> Can you make and test a DSA patch? If we have two concrete things and
> I can sketch two more out of the above that should meet Greg's "need 4
> things" general thinking for driver core API changes.
Working on it. Having device_driver_attach() exported will definitely
make things easier on my side. Thanks for doing the heavy lifting.
>
> But I still would like to keep this going while we wait for acks, you
> know how long that can take...
>
> Jason
next prev parent reply other threads:[~2021-04-29 0:00 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 20:00 [PATCH v2 00/13] Remove vfio_mdev.c, mdev_parent_ops and more Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 01/13] vfio/mdev: Remove CONFIG_VFIO_MDEV_DEVICE Jason Gunthorpe
2021-04-27 11:05 ` Cornelia Huck
2021-04-26 20:00 ` [PATCH v2 02/13] vfio/mdev: Allow the mdev_parent_ops to specify the device driver to bind Jason Gunthorpe
2021-04-27 12:32 ` Cornelia Huck
2021-04-27 23:20 ` Jason Gunthorpe
2021-04-28 6:03 ` Christoph Hellwig
2021-04-28 7:56 ` Dan Williams
2021-04-28 12:41 ` Christoph Hellwig
2021-04-28 14:00 ` Jason Gunthorpe
2021-04-28 19:58 ` Dan Williams
2021-04-28 23:38 ` Jason Gunthorpe
2021-04-29 0:00 ` Dave Jiang [this message]
2021-05-26 0:42 ` Jason Gunthorpe
2021-05-26 1:42 ` Dan Williams
2021-05-27 11:44 ` Christoph Hellwig
2021-05-27 14:53 ` Jason Gunthorpe
2021-05-27 15:13 ` Christoph Hellwig
2021-04-29 6:51 ` Christoph Hellwig
2021-05-04 9:36 ` Christoph Hellwig
2021-05-04 11:30 ` Jason Gunthorpe
2021-04-28 6:44 ` Leon Romanovsky
2021-04-28 14:14 ` Jason Gunthorpe
2021-04-28 14:24 ` Leon Romanovsky
2021-04-26 20:00 ` [PATCH v2 03/13] vfio/mtty: Convert to use vfio_register_group_dev() Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 04/13] vfio/mdpy: " Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 05/13] vfio/mbochs: " Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 07/13] vfio/ccw: " Jason Gunthorpe
2021-04-27 20:06 ` Eric Farman
2021-04-27 22:10 ` Jason Gunthorpe
2021-04-28 12:55 ` Eric Farman
2021-04-28 13:21 ` Jason Gunthorpe
2021-04-28 17:09 ` Cornelia Huck
2021-04-28 17:20 ` Jason Gunthorpe
2021-04-29 11:58 ` Cornelia Huck
2021-04-29 18:13 ` Jason Gunthorpe
2021-04-30 12:31 ` Cornelia Huck
2021-04-30 17:19 ` Jason Gunthorpe
2021-05-03 10:54 ` s390 common I/O layer locking (was: [PATCH v2 07/13] vfio/ccw: Convert to use vfio_register_group_dev()) Cornelia Huck
2021-05-04 15:10 ` s390 common I/O layer locking Vineeth Vijayan
2021-07-24 13:24 ` Christoph Hellwig
2021-08-03 14:27 ` Vineeth Vijayan
2021-08-10 15:00 ` Cornelia Huck
2021-04-26 20:00 ` [PATCH v2 09/13] vfio/mdev: Remove vfio_mdev.c Jason Gunthorpe
2021-04-28 6:07 ` Christoph Hellwig
2021-04-28 6:36 ` Greg Kroah-Hartman
2021-04-28 12:53 ` Jason Gunthorpe
2021-04-29 6:53 ` Christoph Hellwig
2021-04-29 6:56 ` Greg Kroah-Hartman
2021-05-03 17:32 ` Jason Gunthorpe
2021-05-04 9:38 ` Christoph Hellwig
2021-05-04 16:20 ` Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 10/13] vfio/mdev: Remove mdev_parent_ops dev_attr_groups Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 11/13] vfio/mdev: Remove mdev_parent_ops Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 12/13] vfio/mdev: Use the driver core to create the 'remove' file Jason Gunthorpe
2021-04-26 20:00 ` [PATCH v2 13/13] vfio/mdev: Remove mdev drvdata Jason Gunthorpe
2021-04-27 21:30 ` [PATCH v2 00/13] Remove vfio_mdev.c, mdev_parent_ops and more Alex Williamson
2021-04-27 22:20 ` Jason Gunthorpe
2021-04-27 22:49 ` Alex Williamson
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