[PATCH] powerpc/powernv/pci: remove dead code from !CONFIG

Discussion:

[PATCH] powerpc/powernv/pci: remove dead code from !CONFIG_EEH

Nick Desaulniers

2021-04-22 19:54:02 UTC

While looking at -Wundef warnings, the #if CONFIG_EEH stood out as a
possible candidate to convert to #ifdef CONFIG_EEH, but it seems that
based on Kconfig dependencies it's not possible to build this file
without CONFIG_EEH enabled.

Suggested-by: Nathan Chancellor <***@kernel.org>
Suggested-by: Joe Perches <***@perches.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/570
Link: https://lore.kernel.org/lkml/***@perches.com/
Signed-off-by: Nick Desaulniers <***@google.com>
---
arch/powerpc/platforms/powernv/pci.c | 7 -------
1 file changed, 7 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
index 9b9bca169275..591480a37b05 100644
--- a/arch/powerpc/platforms/powernv/pci.c
+++ b/arch/powerpc/platforms/powernv/pci.c
@@ -711,7 +711,6 @@ int pnv_pci_cfg_write(struct pci_dn *pdn,
return PCIBIOS_SUCCESSFUL;
}

-#if CONFIG_EEH
static bool pnv_pci_cfg_check(struct pci_dn *pdn)
{
struct eeh_dev *edev = NULL;
@@ -734,12 +733,6 @@ static bool pnv_pci_cfg_check(struct pci_dn *pdn)

return true;
}
-#else
-static inline pnv_pci_cfg_check(struct pci_dn *pdn)
-{
- return true;
-}
-#endif /* CONFIG_EEH */

static int pnv_pci_read_config(struct pci_bus *bus,
unsigned int devfn,

base-commit: 16fc44d6387e260f4932e9248b985837324705d8
prerequisite-patch-id: 950233069fb22099a8ff8990f620f5c3586a3cbd

--
2.31.1.498.g6c1eba8ee3d-goog

Daniel Axtens

2021-04-22 23:09:12 UTC

Permalink

Hi Nick,

Post by Nick Desaulniers
While looking at -Wundef warnings, the #if CONFIG_EEH stood out as a
possible candidate to convert to #ifdef CONFIG_EEH, but it seems that
based on Kconfig dependencies it's not possible to build this file
without CONFIG_EEH enabled.

This seemed odd to me, but I think you're right:

arch/powerpc/platforms/Kconfig contains:

config EEH
bool
depends on (PPC_POWERNV || PPC_PSERIES) && PCI
default y

It's not configurable from e.g. make menuconfig because there's no prompt.
You can attempt to explicitly disable it with e.g. `scripts/config -d EEH`
but then something like `make oldconfig` will silently re-enable it for
you.

It's been forced on since commit e49f7a9997c6 ("powerpc/pseries: Rivet
CONFIG_EEH for pSeries platform") in 2012 which fixed it for
pseries. That moved out from pseries to pseries + powernv later on.

There are other cleanups in the same vein that could be made, from the
Makefile (which has files only built with CONFIG_EEH) through to other
source files. It looks like there's one `#ifdef CONFIG_EEH` in
arch/powerpc/platforms/powernv/pci-ioda.c that could be pulled out, for
example.

I think it's probably worth trying to rip out all of those in one patch?

Kind regards,
Daniel

Oliver O'Halloran

2021-04-23 01:13:07 UTC

Permalink

Post by Daniel Axtens
Hi Nick,

config EEH
bool
depends on (PPC_POWERNV || PPC_PSERIES) && PCI
default y
It's not configurable from e.g. make menuconfig because there's no prompt.
You can attempt to explicitly disable it with e.g. `scripts/config -d EEH`
but then something like `make oldconfig` will silently re-enable it for
you.
It's been forced on since commit e49f7a9997c6 ("powerpc/pseries: Rivet
CONFIG_EEH for pSeries platform") in 2012 which fixed it for
pseries. That moved out from pseries to pseries + powernv later on.
There are other cleanups in the same vein that could be made, from the
Makefile (which has files only built with CONFIG_EEH) through to other
source files. It looks like there's one `#ifdef CONFIG_EEH` in
arch/powerpc/platforms/powernv/pci-ioda.c that could be pulled out, for
example.
I think it's probably worth trying to rip out all of those in one patch?

The change in commit e49f7a9997c6 ("powerpc/pseries: Rivet CONFIG_EEH
for pSeries platform") never should have been made.

There's no inherent reason why EEH needs to be enabled and forcing it
on is (IMO) a large part of why EEH support is the byzantine
clusterfuck that it is. One of the things I was working towards was
allowing pseries and powernv to be built with !CONFIG_EEH since that
would help define a clearer boundary between what is "eeh support" and
what is required to support PCI on the platform. Pseries is
particularly bad for this since PAPR says the RTAS calls needed to do
a PCI bus reset are part of the EEH extension, but there's non-EEH
reasons why you might want to use those RTAS calls. The PHB reset that
we do when entering a kdump kernel is a good example since that uses
the same RTAS calls, but it has nothing to do with the EEH recovery
machinery enabled by CONFIG_EEH.

I was looking into that largely because people were considering using
OPAL for microwatt platforms. Breaking the assumption that
powernv==EEH support is one of the few bits of work required to enable
that, but even if you don't go down that road I think everyone would
be better off if you kept a degree of separation between the two.

Nick Desaulniers

2021-05-18 00:16:55 UTC

Permalink

Post by Oliver O'Halloran

Post by Daniel Axtens
Hi Nick,

The change in commit e49f7a9997c6 ("powerpc/pseries: Rivet CONFIG_EEH
for pSeries platform") never should have been made.

I'll change my patch to keep the conditionals, but use #ifdef instead
of #if then?

Post by Oliver O'Halloran
There's no inherent reason why EEH needs to be enabled and forcing it
on is (IMO) a large part of why EEH support is the byzantine
clusterfuck that it is. One of the things I was working towards was
allowing pseries and powernv to be built with !CONFIG_EEH since that
would help define a clearer boundary between what is "eeh support" and
what is required to support PCI on the platform. Pseries is
particularly bad for this since PAPR says the RTAS calls needed to do
a PCI bus reset are part of the EEH extension, but there's non-EEH
reasons why you might want to use those RTAS calls. The PHB reset that
we do when entering a kdump kernel is a good example since that uses
the same RTAS calls, but it has nothing to do with the EEH recovery
machinery enabled by CONFIG_EEH.
I was looking into that largely because people were considering using
OPAL for microwatt platforms. Breaking the assumption that
powernv==EEH support is one of the few bits of work required to enable
that, but even if you don't go down that road I think everyone would
be better off if you kept a degree of separation between the two.

--
Thanks,
~Nick Desaulniers

Michael Ellerman

2021-05-18 06:13:50 UTC

Permalink

Post by Nick Desaulniers

Post by Oliver O'Halloran

Post by Daniel Axtens
Hi Nick,

The change in commit e49f7a9997c6 ("powerpc/pseries: Rivet CONFIG_EEH
for pSeries platform") never should have been made.

I'll change my patch to keep the conditionals, but use #ifdef instead
of #if then?

Yeah, please.

I'm not sure I agree with oohal that untangling pseries/powernv from
EEH is something we should do, but let's kick that can down the road by
just fixing up the ifdef.

cheers

Nick Desaulniers

2021-05-18 20:40:41 UTC

Permalink

While looking at -Wundef warnings, the #if CONFIG_EEH stood out as a
possible candidate to convert to #ifdef CONFIG_EEH.

It seems that based on Kconfig dependencies it's not possible to build
this file without CONFIG_EEH enabled, but based on upstream discussion,
it's not clear yet that CONFIG_EEH should be enabled by default.

For now, simply fix the -Wundef warning.

Suggested-by: Nathan Chancellor <***@kernel.org>
Suggested-by: Joe Perches <***@perches.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/570
Link: https://lore.kernel.org/lkml/***@perches.com/
Link: https://lore.kernel.org/lkml/CAOSf1CGoN5R0LUrU=Y=***@mail.gmail.com/
Signed-off-by: Nick Desaulniers <***@google.com>
---
arch/powerpc/platforms/powernv/pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
index b18468dc31ff..6bb3c52633fb 100644
--- a/arch/powerpc/platforms/powernv/pci.c
+++ b/arch/powerpc/platforms/powernv/pci.c
@@ -711,7 +711,7 @@ int pnv_pci_cfg_write(struct pci_dn *pdn,
return PCIBIOS_SUCCESSFUL;
}

-#if CONFIG_EEH
+#ifdef CONFIG_EEH
static bool pnv_pci_cfg_check(struct pci_dn *pdn)
{
struct eeh_dev *edev = NULL;

--
2.31.1.751.gd2f1c929bd-goog

Nathan Chancellor

2021-05-18 20:41:49 UTC

Permalink

Post by Nick Desaulniers
While looking at -Wundef warnings, the #if CONFIG_EEH stood out as a
possible candidate to convert to #ifdef CONFIG_EEH.
It seems that based on Kconfig dependencies it's not possible to build
this file without CONFIG_EEH enabled, but based on upstream discussion,
it's not clear yet that CONFIG_EEH should be enabled by default.
For now, simply fix the -Wundef warning.
Link: https://github.com/ClangBuiltLinux/linux/issues/570

Makes sense, thanks for the patch!

Post by Nick Desaulniers
---
arch/powerpc/platforms/powernv/pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
index b18468dc31ff..6bb3c52633fb 100644
--- a/arch/powerpc/platforms/powernv/pci.c
+++ b/arch/powerpc/platforms/powernv/pci.c
@@ -711,7 +711,7 @@ int pnv_pci_cfg_write(struct pci_dn *pdn,
return PCIBIOS_SUCCESSFUL;
}
-#if CONFIG_EEH
+#ifdef CONFIG_EEH
static bool pnv_pci_cfg_check(struct pci_dn *pdn)
{
struct eeh_dev *edev = NULL;

Michael Ellerman

2021-06-06 12:08:40 UTC

Permalink

Applied to powerpc/next.

[1/1] powerpc/powernv/pci: fix header guard
https://git.kernel.org/powerpc/c/73e6e4e01134c9ee97433ad1f470c71b0748b08f

cheers