[PATCH] firmware/psci: Add debugfs support to ease debugging

[Florian Fainelli]

On 7/28/22 02:20, Dmitry Baryshkov wrote:
> On Thu, 28 Jul 2022 at 12:08, Sudeep Holla <sudeep.holla at arm.com> wrote:
>>
>> On Wed, Jul 27, 2022 at 11:09:01PM +0300, Dmitry Baryshkov wrote:
>>> To ease debugging of PSCI supported features, add debugfs file called
>>> 'psci' describing PSCI and SMC CC versions
>>
>> These 2 are for sure in the boot log. Having them is debugfs accessible
>> via file system add not much value as we would hit issues quite early in
>> the boot for most of the things related to PSCI.
> 
> Yes, it was just to have all the information in a single place.
> 
>>> enabled features and options.
>>>
>>
>> We have psci_checker.c which does some minimal testing of PSCI. I prefer
>> to add things to that rather than a debugfs as it is run during boot. IMO
>> it is usual useful to debug things that cause boot issue most of the time.
>> I am not against this so I will leave it to the maintainers.
> 
> In my case I was not debugging the boot issues (which of course would
> have required a different approach), but I was trying to understand
> runtime capabilities, thus debugfs fits pretty well.
> 
> Another point for the debugfs entry: most of the people run the kernel
> with the psci_checker being turned off, but with debugfs being
> enabled. If we are trying to narrow down firmware capabilities of the
> random device, it is much easier to ask them to cat the dbeugfs file
> rather than to rebuild the kernel.
> 

Yes I would agree with both of those points, in fact, I would go one step further and add the ability to probe an arbitrary PSCI function ID, since deployed firmware typically go beyond the standard PSCI scope and implement a variety of custom extensions (at least we do).

Thanks!
-- 
Florian