Re: [PATCH v3] perf: Add Arm Bus Monitor Unit driver

[Robin Murphy <robin.murphy@arm.com>]

On 04/10/2026 11:10 pm, Will Deacon wrote:
> On Thu, Sep 17, 2026 at 02:47:12PM +0100, Robin Murphy wrote:
>> Arm's Bus Monitor Unit is a low-level performance analysis tool for
>> matching and counting transactions at interconnect interfaces. Each
>> BMU consists of a number of "interface monitoring units", with some
>> global controls to synchronise them and so permit accurate calculation
>> of cross-interface metrics. Each IMU contains, among other things, its
>> own PMU largely based on the CoreSight PMU architecture, but with some
>> functional incompatibilities due to the nature of how much per-event
>> filtering needs to be crammed in to categorise AXI/CHI transactions at
>> the protocol level. As such it gets an honorary home in arm_cspmu/ in
>> order to share the common register definitions, but for simplicity does
>> not try to bend the functional abstraction to fit.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>>
>> ---
>> v3:
>>   - Couple of inconsequential tweaks to shut Sashiko up about things
>>     that would never actually happen anyway
>>   - Drop unneeded DT patches that I can't be bothered to fix right now
> 
> Please can you take a look at the Sashiko comments on this one?

I did start writing a reply at the time, but it was getting so sarcastic 
that even I thought better of sending it...

In (polite) summary:

1 - Gibberish
2 - Yes if firmware blatantly mis-describes the hardware then Linux may 
not work properly. Whoop de do.
3 - Yeah so?
4 - Pants-on-head gibberish, but the second part about COMPILE_TEST is 
fair (an oversight from ripping out the DT support) - fix is already in 
-next via the ACPI tree[1]
5 - Yeah so?
6,7 - Yes, welcome to perf...

Cheers,
Robin.

[1] 
https://lore.kernel.org/all/CAJZ5v0g4k6FhyQMypkRyVJMkSBUsmeuetJuxRA826PcA7Mo5Hg@mail.gmail.com/