On 18/03/2024 1:49 pm, Steven Price wrote:
On 18/03/2024 13:08, Boris Brezillon wrote:
On Mon, 18 Mar 2024 11:31:05 +0000
Steven Price <steven.price@xxxxxxx> 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@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202403031944.EOimQ8WK-lkp@xxxxxxxxx/
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
---
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.
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.
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 :)
FWIW from a quick look it might be cleaner to store the struct page
pointer for the dummy page - especially since the VA only seems to be
used once in panthor_device_init() anyway - then use page_to_pfn() at
the business end.
Cheers,
Robin.
