Re: [dpdk-dev] [PATCH v4 08/12] raw/ioat: add bus driver for device scanning automatically

[Thomas Monjalon <thomas@monjalon.net>]

30/04/2021 17:06, Bruce Richardson:
> Rather than using a vdev with args, DPDK can scan and initialize the
> devices automatically using a bus-type driver. This bus does not need to
> worry about registering device drivers, rather it can initialize the
> devices directly on probe.
> 
> The device instances (queues) to use are detected from /dev with the
> additional info about them got from /sys.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
> --- a/doc/guides/rawdevs/ioat.rst
> +++ b/doc/guides/rawdevs/ioat.rst
> @@ -78,7 +78,7 @@ Example configuration for a work queue::
>  
>          $ accel-config config-wq dsa0/wq0.0 --group-id=0 \
>             --mode=dedicated --priority=10 --wq-size=8 \
> -           --type=user --name=app1
> +           --type=user --name=dpdk_app1

It looks to belong to commit "make workqueue name configurable in script".

>  Once the devices have been configured, they need to be enabled::
>  
> @@ -114,15 +114,18 @@ the device driver on the EAL commandline, via the ``allowlist`` or ``-a`` flag e
>  
>  	$ dpdk-test -a <b:d:f>,max_queues=4
>  
> -If the device is bound to the IDXD kernel driver (and previously configured with sysfs),
> -then a specific work queue needs to be passed to the application via a vdev parameter.
> -This vdev parameter take the driver name and work queue name as parameters.
> -For example, to use work queue 0 on Intel\ |reg| DSA instance 0::
> -
> -        $ dpdk-test --no-pci --vdev=rawdev_idxd,wq=0.0
> -
> -Once probed successfully, the device will appear as a ``rawdev``, that is a
> -"raw device type" inside DPDK, and can be accessed using APIs from the
> +For devices bound to the IDXD kernel driver,
> +the DPDK ioat driver will automatically perform a scan for available workqueues to use.
> +Any workqueues found listed in ``/dev/dsa`` on the system will be checked in ``/sys``,
> +and any which have ``dpdk_`` prefix in their name will be automatically probed by the
> +driver to make them available to the application.
> +Alternatively, to support use by multiple DPDK processes simultaneously,
> +the value used as the DPDK ``--file-prefix`` parameter may be used as a workqueue name prefix,
> +instead of ``dpdk_``,
> +allowing each DPDK application instance to only use a subset of configured queues.
> +
> +Once probed successfully, irrespective of kernel driver, the device will appear as a ``rawdev``,
> +that is a "raw device type" inside DPDK, and can be accessed using APIs from the
>  ``rte_rawdev`` library.
[...]
> --- a/drivers/raw/ioat/meson.build
> +++ b/drivers/raw/ioat/meson.build
> @@ -4,13 +4,13 @@
>  build = dpdk_conf.has('RTE_ARCH_X86')
>  reason = 'only supported on x86'
>  sources = files(
> +        'idxd_bus.c',
>          'idxd_pci.c',
> -        'idxd_vdev.c',
>          'ioat_common.c',
>          'ioat_rawdev.c',
>          'ioat_rawdev_test.c',
>  )
> -deps += ['bus_pci', 'bus_vdev', 'mbuf', 'rawdev']
> +deps += ['bus_pci', 'mbuf', 'rawdev']

OK to remove the vdev dependency by creating a bus singleton.

You may want to allow iterating devices of the bus
by implementing .dev_iterate callback.