Re: [PATCH v2 09/21] ath10k: print fw debug messages in hex.

["Grumbach, Emmanuel" <emmanuel.grumbach@intel.com>]

On Thu, 2016-09-15 at 10:59 -0700, Ben Greear wrote:
> On 09/15/2016 10:34 AM, Grumbach, Emmanuel wrote:
> > On Thu, 2016-09-15 at 08:14 -0700, Ben Greear wrote:
> > > On 09/15/2016 07:06 AM, Valo, Kalle wrote:
> > > > Ben Greear <greearb@candelatech.com> writes:
> > > > 
> > > > > On 09/14/2016 07:18 AM, Valo, Kalle wrote:
> > > > > > greearb@candelatech.com writes:
> > > > > > 
> > > > > > > From: Ben Greear <greearb@candelatech.com>
> > > > > > > 
> > > > > > > This allows user-space tools to decode debug-log
> > > > > > > messages by parsing dmesg or /var/log/messages.
> > > > > > > 
> > > > > > > Signed-off-by: Ben Greear <greearb@candelatech.com>
> > > > > > 
> > > > > > Don't tracing points already provide the same information?
> > > > > 
> > > > > Tracing tools are difficult to set up and may not be
> > > > > available on
> > > > > random embedded devices.  And if we are dealing with bug
> > > > > reports
> > > > > from
> > > > > the field, most users will not be able to set it up
> > > > > regardless.
> > > > > 
> > > > > There are similar ways to print out hex, but the logic below
> > > > > creates
> > > > > specific and parseable logs in the 'dmesg' output and
> > > > > similar.
> > > > > 
> > > > > I have written a tool that can decode these messages into
> > > > > useful
> > > > > human-readable
> > > > > text so that I can debug firmware issues both locally and
> > > > > from
> > > > > field reports.
> > > > > 
> > > > > Stock firmware generates similar logs and QCA could write
> > > > > their
> > > > > own decode logic
> > > > > for their firmware versions.
> > > > 
> > > > Reinventing the wheel by using printk as the delivery mechanism
> > > > doesn't
> > > > sound like a good idea. IIRC Emmanuel talked about some kind of
> > > > firmware
> > > > debugging framework, he might have some ideas.
> > > 
> > > Waiting for magical frameworks to fix problems is even worse.
> > > 
> > It has been years since ath10k has been in the kernel.  There is
> > > basically
> > > still no way to debug what the firmware is doing.
> > > 
> > 
> > I know the feeling :) I was in the same situation before I added
> > stuff
> > for iwlwifi.
> > 
> > > My patch gives you something that can work right now, with the
> > > standard 'dmesg'
> > > framework found in virtually all kernels new and old, and it has
> > > been
> > > proven
> > > to be useful in the field.  The messages are also nicely
> > > interleaved
> > > with the
> > > rest of the mac80211 stack messages and any other driver
> > > messages, so
> > > you have
> > > context.
> > > 
> > > If someone wants to add support for a framework later, then by
> > > all
> > > means, post
> > > the patches when it is ready.
> > 
> > From my experience, a strong and easy-to-use firmware debug
> > infrastructure is important because typically, the firmware is
> > written
> > by other people who have different priorities (and are not always
> > Linux
> > wizards) etc... Being able to give them good data is the only way
> > to
> > have them fix their bugs :) For us, it was really a game changer.
> > When
> > you work for a big corporate, having 2 groups work better together
> > always has a big impact. That's for the philosophical part :)
> > 
> > FWIW: what I did has nothing to do with FW 'live tracing', but with
> > firmware dumps. One part of our firmware dumps include tracing. We
> > also
> > have "firmware prints", but we don't print them in the kernel log
> > and
> > they are not part of the firmware dump thing. We rather record them
> > in
> > tracepoints just like really *anything* that comes from the
> > firmware.
> > Basically, we have 2 layers, the transport layer (PCIe) and the
> > operation_mode layer. The first just brings the data from the
> > firmware
> > and in that layer we *blindly* record everything in tracepoints. In
> > the
> > operation_mode layer, we look at the data itself. In case of debug
> > prints from the firmware, we simply discard them, because we don't
> > really care of the meaning. All we want is to have them go through
> > the
> > PCIe layer so that they are recorded in the tracepoints.
> > When we finish recording the sequence we wanted with tracing (trace
> > -cmd), we parse the output and then, we parse the firmware prints.
> > IMHO, this is more reliable than kernel logs and you don't lose the
> > alignment with the driver traces as long as you have driver data in
> > tracepoints as well.
> 
> I have other patches that remember the last 100 or so firmware log
> messages from
> the kernel and provide that in a binary dump image when firmware
> crashes.
> 
> This is indeed very useful.
> 
> But, when debugging non-crash occasions, it is still useful to see
> what
> the firmware is doing.
> 

For that, I have come up with the "triggers". Triggers are conditions
that can be detected by the driver and enabled by the user. So
basically, we can say: "Please dump the logs when you are deauth'ed by
the AP". Or when you get delBA, or when the stats that come up from the
firmware say such and such etc... There are hooks that I added in
mac80211 to let the driver know about events that are handled there
(MLME and friends). Then, even if your logs are stored in a cyclic
buffer, you don't miss them and you catch them at the right spot.
One of the most useful trigger we have is when a Tx packet is dropped.
You can take a look at struct iwl_fw_dbg_trigger_tlv in iwlwifi if you
want.

> For instance, maybe it is reporting lots of tx-hangs and/or low-level
> resets.  This gives you a clue as to why a user might report 'my wifi
> sucks'.
> > Since I am both FW and driver team for my firmware variant,
> and my approach has been working for me, then I feel it is certainly
> better than
> the current state.  And just maybe the official upstream FW team
> could start
> using something similar as well.  Currently, I don't see how they can
> ever make
> much progress on firmware crashes reported in stock kernels.
> > Thanks,
> Ben
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