Re: Firmware debugging patches?

[Ben Greear <greearb@candelatech.com>]

On 06/02/2014 11:46 AM, Emmanuel Grumbach wrote:
>> [Good stuff snipped, adding linux-wireless as this is a more
>> general issue if we are going to consider general framework]
>>
>>
>> Maybe we should start with goals before getting to implementation
>> details.  Here's my wish list that is ath10k specific, but probably
>> similar to other firmware users:
>>
>> 1)  We need the firmware crash text currently printed to
>> /var/log/messages.
>>
>> 2)  It would be nice to get the firmware RAM and stack dumps at time of
>> crash to debug more interesting crashes.
> 
> Right - but typically you'll have closed source / IP / whatever there..

I mean that we need the raw data (ie, binary dump, something printed
in ascii-hex, etc).  I understand it will take proprietary tools to
decode it to something a developer can actually debug.

>> 3)  It would be nice to know about firmware debug messages for
>> the period of time directly before the crash (maybe 2-5 minutes?)
>>
>> 4)  It would be nice to have this interleaved with kernel, supplicant,
>> and related logs.
>>
>>
>> We need a solution for different types of users.  I suspect the number
>> of crashes seen in the wild will be more for users nearer the top
>> of this list.
>>
>> a) Normal Fedora/Ubuntu/etc default-installed distribution user
>> with ath10k NIC has wifi issues, firmware crashes, they don't
>> really know what firmware means or that it crashed, but some automated crash-log
>> tool notices and gathers debug info for automated bug reporting.
> 
> I am working on that for our firmware. I recently added such capability relying on udev to notify the userspace that something bad happens. I gather all the data and prepare a binary file that is sent through debugfs (pulled by a script triggered by udev). I remember the first crash only.

How is this binary blob encoded?

At least for drivers that can recover from firmware crashes, I think
we should continue to report crashes, not just the first.

Maybe could store another one after initial crash has been read
and 1 minute has elapsed, or if initial crash has not been read
in 1 day, or something like that.

Also, if we use debugfs then we require upstream kernels to have this
compiled in and mounted if we want to handle this class of user.

I am not sure this is really the case currently.  But, once the
blob is generated and stored in RAM, it would be easily enough to
add ethtool option to dump it w/out debugfs support.  This will
still not really address my concerns because it may take a year
or two for the latest ethtool binary to make it to normal-ish users.

>>
>> b) Slightly more advanced user actually notices the problem at coffee shop
>> earlier today, posts about it when they get home, and we ask for
>> debug info.
>>
>> c) Experienced and determined user has similar issues, but is able to
>> reproduce the problem and/or turn on more advanced debugging efforts.
>>
>> d)  Even more determined user that can and will recompile kernels and/or
>> try patches.
>>
>>
>> Anything that has to be enabled before-hand will not help a) and b) above.
>>
>> If support is not compiled into default kernels, c) will not help you either.
>>
>> If it is difficult or requires acquiring cutting edge tools not in their
>> distribution by default, many of c) and some of d) will just ignore the problem or use
>> different hardware.
>>
>> If we are storing crashes for something like ethtool to report, we need
>> RAM and/or disk storage so the firmware RAM dumps and such can be stored until
>> the user and/or automated tools ask for them.  We need some way to automatically
>> clean up old crashes so disk/ram is not overly utilized.  For APs,
>> they are low on both RAM and 'disk', so storing crash logs for any
>> length of time may be problematic.
>  
> I did something simpler - but it works. I don't really know the ethtool infrastructure though.

I think ethtool would not be overly hard to implement...basic framework is already
in the wifi stack.

Thanks,
Ben


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com