[dpdk-dev] [PATCH 6/6] doc: introduction to prgdev

Thomas Monjalon thomas.monjalon at 6wind.com
Mon Mar 6 16:26:37 CET 2017

2017-03-02 12:03, Chen Jing D:
> +Overview
> +========

I think the first review pass of this series must be focused on the
overview you give here (thanks for the detailed explanations).

I'll try to sum up while commenting.

The target is programmable devices.

> +The major purpose of prgdev is to help DPDK users to load/upgrade RTL images
> +for FPGA devices, or upgrade firmware for programmble NICs.

This is a control plane feature.
You want to have it in DPDK to allow dynamic programmation while running
the device, right?

> +When the set of APIs is introduced, a general question is why we need it in
> +DPDK community?

Good question :)

> +Any devices, having the capability to store/load a piece of info to/from
> +the deivce then changed hardware behavior, and applicable to prgdev programming
> +model, could be registered as a prgdev device.
> +
> +The device can be programmed (dynamic) within DPDK or have been prior programmed
> +(static) prior to a DPDK application being launched.
> +Besides the simple API to upload/download image, the prgdev also introduces a
> +mechanism internally to switch drivers and register/unregister device on the
> +fly. With this mechanism, apps can use the programmable device, unbind other
> +personalities on demand, then program it and bind it back with new personalities.
> +Apps can follow below examples to simply complete the whole process.

I disagree about the specific bind/unbind for prgdev.
We must improve binding inside DPDK for every devices.

> +Note that bind/unbind actions are different concept from that a whole device
> +attach/detach. For example, ``rte_eal_dev_detach()``, which will try to detach the
> +drivers with device and remove the whole device from specific class of devices
> +(ethdev, for example). Then, the whole device is invisible until a new 'probe'
> +is activated.

I do not understand.

> +During the whole procedure of image upload/download, prgdev handler is always
> +valid and apps can use it operate on programmable device. The reason why unbind
> +is necessary is it may break the hardware when programming is in progress while
> +other functions are active. Using programmble NIC as an example, it's a little
> +impossible to receive/forward packets for hardware while updating firmware. In
> +this case, apps need to detach ethdev function before firmware upgrading. Again,
> +prgdev handler is still valid, it's function-level detach, different from
> +device-level detach. After finishing image download, original function needs to
> +attach back, either use same or different drivers, depends on personalities
> +changed or not. For a programmble NIC, the driver may be the same. For FPGA, it
> +may not, see below examples to get more details.

If the personality of the device is changed, it must be seen as a new device
from e.g. the ethdev point of view, while keeping the same prgdev device.
In other words, a device can have several interfaces at the same time
(ethdev, cryptodev, eventdev, prgdev, whatever).
I think we can dynamically create/destroy some interfaces while keeping track
of the underlying device.

> +Another reason to provide bind/unbind action is programmble devices, like FPGA,
> +are not identified driver by 'vendor ID' and 'device ID', they might not be
> +changed in all the ways, even FPGA is fully programmed. So, it depends on
> +internal mechanism of FPGA, not 'vendor ID' and 'device ID' to identify proper
> +drivers, either a register value or signature, depending on FPGA hardware
> +design. In this case, EAL or other bus driver doesn't have the capability to
> +identify proper driver for FPGA device. With prgdev introduced, while FPGA is
> +always a prgdev, FPGA can use prgdev as primary driver, to find proper function
> +driver.

You mean prgdev should help the bus layer to map the right driver interface?
It looks weird and dangerous. The standard way to identify a PCI device is
to look at its IDs. Other unknown methods must be strongly discussed.

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