On 3/29/2018 8:13 PM, Andrew Lunn wrote:

On Thu, Mar 29, 2018 at 07:07:43PM +0300, Alex Vesker wrote:

quoted

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.

Hi Alex

So the device is in change of making a snapshot? A user cannot
initiate it?

Hi,
Correct, currently the user cannot initiate saving a snapshot but
as I said in the cover letter, planned support is for dumping "live" 
regions.

Seems like if i'm trying to debug something, i want to take a snapshot
in the good state, issue the command which breaks things, and then
take another snapshot. Looking at the diff then gives me an idea what
happened.

quoted

Show all of the exposed regions with region sizes:
$ devlink region show
pci/0000:00:05.0/cr-space: size 1048576 snapshot [1 2]

So you have 2Mbytes of snapshot data. Is this held in the device, or
kernel memory?

This is allocated in devlink, the maximum number of snapshots is set by 
the driver.

quoted

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

Why a separate command? It seems to be just a subset of dump.

This is useful when debugging values on specific addresses, this also
brings the API one step closer for a read and write API.

     Andrew