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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

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.