netdev - Re: [PATCH net-next v2 00/11] devlink: Add support for region access

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Date:   Wed, 11 Jul 2018 11:48:27 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Alex Vesker <valex@...lanox.com>
Cc:     netdev@...r.kernel.org, jiri@...lanox.com, dsahern@...il.com,
        andrew@...n.ch, rahul.lakkireddy@...lsio.com,
        linux-wireless@...r.kernel.org,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH net-next v2 00/11] devlink: Add support for region
 access

CC: linux-wireless, wifi chips used to have similar problem

On Wed, 11 Jul 2018 13:42:57 +0300, Alex Vesker wrote:
> This is a proposal which will allow access to driver defined address
> regions using devlink. Each device can create its supported address
> regions and register them. A device which exposes a region will allow
> access to it using devlink.
> 
> The suggested implementation will allow exposing regions to the user,
> reading and dumping snapshots taken from different regions. 
> A snapshot represents a memory image of a region taken by the driver.
> 
> If a device collects a snapshot of an address region it can be later
> exposed using devlink region read or dump commands.
> This functionality allows for future analyses on the snapshots to be
> done.
> 
> The major benefit of this support is not only to provide access to
> internal address regions which were inaccessible to the user but also
> to provide an additional way to debug complex error states using the
> region snapshots.
> 
> Implemented commands:
> $ devlink region help
> $ devlink region show [ DEV/REGION ]
> $ devlink region del DEV/REGION snapshot SNAPSHOT_ID
> $ devlink region dump DEV/REGION [ snapshot SNAPSHOT_ID ]
> $ devlink region read DEV/REGION [ snapshot SNAPSHOT_ID ]
> 	address ADDRESS length length

You got me excited with the read without snapshot but then you say below
that it's future work :)

> Show all of the exposed regions with region sizes:
> $ devlink region show
> pci/0000:00:05.0/cr-space: size 1048576 snapshot [1 2]
> pci/0000:00:05.0/fw-health: size 64 snapshot [1 2]
> 
> Delete a snapshot using:
> $ devlink region del pci/0000:00:05.0/cr-space snapshot 1
> 
> Dump a snapshot:
> $ devlink region dump pci/0000:00:05.0/fw-health snapshot 1
> 0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30
> 0000000000000010 0000 0000 ffff ff04 0029 8c00 0028 8cc8
> 0000000000000020 0016 0bb8 0016 1720 0000 0000 c00f 3ffc
> 0000000000000030 bada cce5 bada cce5 bada cce5 bada cce5
> 
> Read a specific part of a snapshot:
> $ devlink region read pci/0000:00:05.0/fw-health snapshot 1 address 0 
> 	length 16
> 0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30
> 
> For more information you can check devlink-region.8 man page
> 
> Future:
> There is a plan to extend the support to include a write command
> as well as performing read and dump live region

Reading live region would be very interesting and alleviate the need
for complicated ethtool dump marshalling a number of drivers started
doing (incl. nfp).  Any plans on that?

Write support I'm less excited about :)