Re: [dpdk-dev] [EXT] Re: [PATCH v3 1/5] net/enetfec: introduce NXP ENETFEC driver

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/1/2021 11:22 AM, Apeksha Gupta wrote:
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Thursday, September 23, 2021 3:40 PM
>> To: Apeksha Gupta <apeksha.gupta@nxp.com>;
>> david.marchand@redhat.com; andrew.rybchenko@oktetlabs.ru;
>> ferruh.yigit@intel.com
>> Cc: dev@dpdk.org; Sachin Saxena <sachin.saxena@nxp.com>; Hemant
>> Agrawal <hemant.agrawal@nxp.com>
>> Subject: [EXT] Re: [dpdk-dev] [PATCH v3 1/5] net/enetfec: introduce NXP
>> ENETFEC driver
>>
>> Caution: EXT Email
>>
>> On 9/9/2021 9:43 PM, Apeksha Gupta wrote:
>>> ENETFEC (Fast Ethernet Controller) is a network poll mode driver
>>> for NXP SoC i.MX 8M Mini.
>>>
>>
>> Hi Apeksha,
>>
>> Before going into details, I have some high level comments to start with,
>> please
>> find comments below.
>>
>>> This patch adds skeleton for enetfec driver with probe function.
>>>
>>> Signed-off-by: Sachin Saxena <sachin.saxena@nxp.com>
>>> Signed-off-by: Apeksha Gupta <apeksha.gupta@nxp.com>
>>
>> <...>
>>
>>> +++ b/doc/guides/nics/enetfec.rst
>>> @@ -0,0 +1,122 @@
>>> +.. SPDX-License-Identifier: BSD-3-Clause
>>> +   Copyright 2021 NXP
>>> +
>>> +ENETFEC Poll Mode Driver
>>> +========================
>>> +
>>> +The ENETFEC NIC PMD (**librte_net_enetfec**) provides poll mode
>> driver
>>> +support for the inbuilt NIC found in the ** NXP i.MX 8M Mini** SoC.
>>> +
>>> +More information can be found at NXP Official Website
>>>
>> +<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fw
>> ww.nxp.com%2Fproducts%2Fprocessors-and-microcontrollers%2Farm-
>> processors%2Fi-mx-applications-processors%2Fi-mx-8-processors%2Fi-mx-
>> 8m-mini-arm-cortex-a53-cortex-m4-audio-voice-
>> video%3Ai.MX8MMINI&amp;data=04%7C01%7Capeksha.gupta%40nxp.com
>> %7C74fdc59c47574d828f7608d97e7a4df3%7C686ea1d3bc2b4c6fa92cd99c5c30
>> 1635%7C0%7C1%7C637679886024819097%7CUnknown%7CTWFpbGZsb3d8ey
>> JWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%
>> 7C3000&amp;sdata=TjuqIfC8yXwBa3DLCgA7djItfV0UmZ6lA3uLDQ7TFwY%3D
>> &amp;reserved=0>
>>> +
>>> +ENETFEC
>>> +-------
>>> +
>>> +This section provides an overview of the NXP ENETFEC and how it is
>>> +integrated into the DPDK.
>>> +
>>> +Contents summary
>>> +
>>> +- ENETFEC overview
>>> +- ENETFEC features
>>> +- Supported ENETFEC SoCs
>>> +- Prerequisites
>>> +- Driver compilation and testing
>>> +- Limitations
>>> +
>>> +ENETFEC Overview
>>> +~~~~~~~~~~~~~~~~
>>> +The i.MX 8M Mini Media Applications Processor is built to achieve both
>> high
>>> +performance and low power consumption. ENETFEC is a hardware
>> programmable
>>> +packet forwarding engine to provide high performance Ethernet interface.
>>
>> It has 1Gbps interface, right? It can be good to give more details on the
>> Ethernet interface.
> [Apeksha] Okay.
>>
>>> +The diagram below shows a system level overview of ENETFEC:
>>> +
>>> +
>> ====================================================+=====
>> ==========
>>> +   US   +-----------------------------------------+    | Kernel Space
>>> +     |                                         |    |
>>> +     |               ENETFEC Driver            |    |
>>> +     +-----------------------------------------+    |
>>> +                       ^   |                        |
>>> +   ENETFEC         RXQ |   | TXQ                    |
>>> +   PMD                         |   |                        |
>>> +                       |   v                        |   +----------+
>>> +                  +-------------+                   |   | fec-uio  |
>>> +                  | net_enetfec |                   |   +----------+
>>> +                  +-------------+                   |
>>> +                       ^   |                        |
>>> +                   TXQ |   | RXQ                    |
>>> +                       |   |                        |
>>> +                       |   v                        |
>>> +
>> ===================================================+======
>> =========
>>> +      +----------------------------------------+
>>> +      |                                        |       HW
>>> +      |           i.MX 8M MINI EVK             |
>>> +      |               +-----+                  |
>>> +      |               | MAC |                  |
>>> +      +---------------+-----+------------------+
>>> +                      | PHY |
>>> +                      +-----+
>>> +
>>> +ENETFEC Ethernet driver is traditional DPDK PMD driver running in the
>> userspace.
>>> +The MAC and PHY are the hardware blocks. 'fec-uio' is the UIO driver,
>> ENETFEC PMD
>>> +uses UIO interface to interact with kernel for PHY initialisation and for
>> mapping
>>> +the allocated memory of register & BD in kernel with DPDK which gives
>> access to
>>> +non-cacheable memory for BD.
>>
>> Why a specific uio driver, 'fec-uio', is required? I think this is the major
>> issue to clarify to proceed.
>>
>> In DPDK we have full framework to support uio, to do the all memory
>> mapping,
>> interrupt configuration etc..., common to all drivers.
>> But in this case driver is implemented as virtual driver and it handles its own
>> uoi handling itself. Why the driver can't use existing support and
>> implemented
>> as physical driver?
> [Apeksha] Yes you are correct. As per our knowledge, UIO framework is there for VM & PCI bus devices and not for vdev bus devices. 

That is part of the comment, why driver implemented as vdev instead of physical
device?
What is the actual device bus?