[PATCH] drm/panthor: Fix the CONFIG_PM=n case

[Boris Brezillon]

On Mon, 18 Mar 2024 13:49:52 +0000
Steven Price <steven.price at arm.com> wrote:

> On 18/03/2024 13:08, Boris Brezillon wrote:
> > On Mon, 18 Mar 2024 11:31:05 +0000
> > Steven Price <steven.price at arm.com> wrote:
> >   
> >> On 18/03/2024 08:58, Boris Brezillon wrote:  
> >>> Putting a hard dependency on CONFIG_PM is not possible because of a
> >>> circular dependency issue, and it's actually not desirable either. In
> >>> order to support this use case, we forcibly resume at init time, and
> >>> suspend at unplug time.
> >>>
> >>> Reported-by: kernel test robot <lkp at intel.com>
> >>> Closes: https://lore.kernel.org/oe-kbuild-all/202403031944.EOimQ8WK-lkp@intel.com/
> >>> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>    
> >>
> >> Reviewed-by: Steven Price <steven.price at arm.com>
> >>  
> >>> ---
> >>> Tested by faking CONFIG_PM=n in the driver (basically commenting
> >>> all pm_runtime calls, and making the panthor_device_suspend/resume()
> >>> calls unconditional in the panthor_device_unplug/init() path) since
> >>> CONFIG_ARCH_ROCKCHIP selects CONFIG_PM. Seems to work fine, but I
> >>> can't be 100% sure this will work correctly on a platform that has
> >>> CONFIG_PM=n.    
> >>
> >> The same - I can't test this properly :(
> >>
> >> Note that the other option (which AFAICT doesn't cause any problems) is
> >> to "select PM" rather than depend on it - AIUI the 'select' dependency
> >> is considered in the opposite direction by kconfig so won't cause the
> >> dependency loop.  
> > 
> > Doesn't seem to work with COMPILE_TEST though? I mean, we need
> > something like
> > 
> > 	depends on ARM || ARM64 || (COMPILE_TEST && PM)
> > 	...
> > 	select PM
> > 
> > but kconfig doesn't like that  
> 
> Why do we need the "&& PM" part? Just:
> 
> 	depends on ARM || ARM64 || COMPILE_TEST
> 	...
> 	select PM
> 
> Or at least that appears to work for me.

Uh, you're right, sorry for the brain fart. This is being said, I
see no other driver selecting the PM option directly (if you grep for
'select PM' in drivers/, you'll find occurrences in drivers/soc, but
those are under ARCH_/SOC_ options, which means they are indirectly
arch/platform dependent, not driver dependent). I'm really not sure
selecting PM here from a driver is right to be honest.

> 
> > drivers/gpu/drm/panthor/Kconfig:3:error: recursive dependency detected!
> > drivers/gpu/drm/panthor/Kconfig:3:	symbol DRM_PANTHOR depends on
> > PM kernel/power/Kconfig:183:	symbol PM is selected by DRM_PANTHOR
> > 
> > which id why I initially when for a depends on PM
> > 
> >   
> >> Of course if there is actually anyone who has a
> >> platform which can be built !CONFIG_PM then that won't help. But the
> >> inability of anyone to actually properly test this configuration does
> >> worry me a little.  
> > 
> > Well, as long as it doesn't regress the PM behavior, I think I'm happy
> > to take the risk. Worst case scenario, someone complains that this is
> > not working properly when they do the !PM bringup :-).  
> 
> Indeed, I've no objection to this patch - although I really should have
> compiled tested it as Robin pointed out ;)
> 
> But one other thing I've noticed when compile testing it - we don't
> appear to have fully fixed the virt_to_pfn() problem. On x86 with
> COMPILE_TEST I still get an error. Looking at the code it appears that
> virt_to_pfn() isn't available on x86... it overrides asm/page.h and
> doesn't provide a definition. The definition on x86 is hiding in
> asm/xen/page.h.

Looks like the kbuild bot didn't catch that yet :-).

> 
> Outside of arch code it's only drivers/xen that currently uses that
> function. So I guess it's probably best to do a
> PFN_DOWN(virt_to_phys(...)) instead. Or look to fix x86 :)

Mind sending a fix for that?