linux-stable.git/arch/powerpc/kernel/Makefile, branch v5.13.2 Linux kernel stable tree powerpc/vdso: Make sure vdso_wrapper.o is rebuilt everytime vdso.so is rebuilt 2021-04-01T13:18:09+00:00 Christophe Leroy christophe.leroy@csgroup.eu 2021-03-31T09:12:19+00:00 791f9e36599d94af5a76d3f74d04e16326761aae Commit bce74491c300 ("powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o") moved vdso32_wrapper.o and vdso64_wrapper.o out of arch/powerpc/kernel/vdso[32/64]/ and removed the dependencies in the Makefile. This leads to the wrappers not being re-build hence the kernel embedding the old vdso library. Add back missing dependencies to ensure vdso32_wrapper.o and vdso64_wrapper.o are rebuilt when vdso32.so.dbg and vdso64.so.dbg are changed. Fixes: bce74491c300 ("powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o") Cc: stable@vger.kernel.org Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/8bb015bc98c51d8ced581415b7e3d157e18da7c9.1617181918.git.christophe.leroy@csgroup.eu 
Commit bce74491c300 ("powerpc/vdso: fix unnecessary rebuilds of
vgettimeofday.o") moved vdso32_wrapper.o and vdso64_wrapper.o out
of arch/powerpc/kernel/vdso[32/64]/ and removed the dependencies in
the Makefile. This leads to the wrappers not being re-build hence the
kernel embedding the old vdso library.

Add back missing dependencies to ensure vdso32_wrapper.o and vdso64_wrapper.o
are rebuilt when vdso32.so.dbg and vdso64.so.dbg are changed.

Fixes: bce74491c300 ("powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8bb015bc98c51d8ced581415b7e3d157e18da7c9.1617181918.git.christophe.leroy@csgroup.eu
Merge tag 'powerpc-5.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux 2021-02-22T22:34:00+00:00 Linus Torvalds torvalds@linux-foundation.org 2021-02-22T22:34:00+00:00 b12b47249688915e987a9a2a393b522f86f6b7ab Pull powerpc updates from Michael Ellerman: - A large series adding wrappers for our interrupt handlers, so that irq/nmi/user tracking can be isolated in the wrappers rather than spread in each handler. - Conversion of the 32-bit syscall handling into C. - A series from Nick to streamline our TLB flushing when using the Radix MMU. - Switch to using queued spinlocks by default for 64-bit server CPUs. - A rework of our PCI probing so that it happens later in boot, when more generic infrastructure is available. - Two small fixes to allow 32-bit little-endian processes to run on 64-bit kernels. - Other smaller features, fixes & cleanups. Thanks to: Alexey Kardashevskiy, Ananth N Mavinakayanahalli, Aneesh Kumar K.V, Athira Rajeev, Bhaskar Chowdhury, Cédric Le Goater, Chengyang Fan, Christophe Leroy, Christopher M. Riedl, Fabiano Rosas, Florian Fainelli, Frederic Barrat, Ganesh Goudar, Hari Bathini, Jiapeng Chong, Joseph J Allen, Kajol Jain, Markus Elfring, Michal Suchanek, Nathan Lynch, Naveen N. Rao, Nicholas Piggin, Oliver O'Halloran, Pingfan Liu, Po-Hsu Lin, Qian Cai, Ram Pai, Randy Dunlap, Sandipan Das, Stephen Rothwell, Tyrel Datwyler, Will Springer, Yury Norov, and Zheng Yongjun. * tag 'powerpc-5.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (188 commits) powerpc/perf: Adds support for programming of Thresholding in P10 powerpc/pci: Remove unimplemented prototypes powerpc/uaccess: Merge raw_copy_to_user_allowed() into raw_copy_to_user() powerpc/uaccess: Merge __put_user_size_allowed() into __put_user_size() powerpc/uaccess: get rid of small constant size cases in raw_copy_{to,from}_user() powerpc/64: Fix stack trace not displaying final frame powerpc/time: Remove get_tbl() powerpc/time: Avoid using get_tbl() spi: mpc52xx: Avoid using get_tbl() powerpc/syscall: Avoid storing 'current' in another pointer powerpc/32: Handle bookE debugging in C in syscall entry/exit powerpc/syscall: Do not check unsupported scv vector on PPC32 powerpc/32: Remove the counter in global_dbcr0 powerpc/32: Remove verification of MSR_PR on syscall in the ASM entry powerpc/syscall: implement system call entry/exit logic in C for PPC32 powerpc/32: Always save non volatile GPRs at syscall entry powerpc/syscall: Change condition to check MSR_RI powerpc/syscall: Save r3 in regs->orig_r3 powerpc/syscall: Use is_compat_task() powerpc/syscall: Make interrupt.c buildable on PPC32 ... 
Pull powerpc updates from Michael Ellerman:

 - A large series adding wrappers for our interrupt handlers, so that
   irq/nmi/user tracking can be isolated in the wrappers rather than
   spread in each handler.

 - Conversion of the 32-bit syscall handling into C.

 - A series from Nick to streamline our TLB flushing when using the
   Radix MMU.

 - Switch to using queued spinlocks by default for 64-bit server CPUs.

 - A rework of our PCI probing so that it happens later in boot, when
   more generic infrastructure is available.

 - Two small fixes to allow 32-bit little-endian processes to run on
   64-bit kernels.

 - Other smaller features, fixes & cleanups.

Thanks to: Alexey Kardashevskiy, Ananth N Mavinakayanahalli, Aneesh
Kumar K.V, Athira Rajeev, Bhaskar Chowdhury, Cédric Le Goater, Chengyang
Fan, Christophe Leroy, Christopher M. Riedl, Fabiano Rosas, Florian
Fainelli, Frederic Barrat, Ganesh Goudar, Hari Bathini, Jiapeng Chong,
Joseph J Allen, Kajol Jain, Markus Elfring, Michal Suchanek, Nathan
Lynch, Naveen N. Rao, Nicholas Piggin, Oliver O'Halloran, Pingfan Liu,
Po-Hsu Lin, Qian Cai, Ram Pai, Randy Dunlap, Sandipan Das, Stephen
Rothwell, Tyrel Datwyler, Will Springer, Yury Norov, and Zheng Yongjun.

* tag 'powerpc-5.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (188 commits)
  powerpc/perf: Adds support for programming of Thresholding in P10
  powerpc/pci: Remove unimplemented prototypes
  powerpc/uaccess: Merge raw_copy_to_user_allowed() into raw_copy_to_user()
  powerpc/uaccess: Merge __put_user_size_allowed() into __put_user_size()
  powerpc/uaccess: get rid of small constant size cases in raw_copy_{to,from}_user()
  powerpc/64: Fix stack trace not displaying final frame
  powerpc/time: Remove get_tbl()
  powerpc/time: Avoid using get_tbl()
  spi: mpc52xx: Avoid using get_tbl()
  powerpc/syscall: Avoid storing 'current' in another pointer
  powerpc/32: Handle bookE debugging in C in syscall entry/exit
  powerpc/syscall: Do not check unsupported scv vector on PPC32
  powerpc/32: Remove the counter in global_dbcr0
  powerpc/32: Remove verification of MSR_PR on syscall in the ASM entry
  powerpc/syscall: implement system call entry/exit logic in C for PPC32
  powerpc/32: Always save non volatile GPRs at syscall entry
  powerpc/syscall: Change condition to check MSR_RI
  powerpc/syscall: Save r3 in regs->orig_r3
  powerpc/syscall: Use is_compat_task()
  powerpc/syscall: Make interrupt.c buildable on PPC32
  ...
powerpc/syscall: Make interrupt.c buildable on PPC32 2021-02-11T12:35:10+00:00 Christophe Leroy christophe.leroy@csgroup.eu 2021-02-08T15:10:28+00:00 344bb20b159dd0996e521c0d4c131a6ae10c322a To allow building interrupt.c on PPC32, ifdef out specific PPC64 code or use helpers which are available on both PP32 and PPC64 Modify Makefile to always build interrupt.o Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/ba073ad67bd971a88ce331b65d6655523b54c794.1612796617.git.christophe.leroy@csgroup.eu 
To allow building interrupt.c on PPC32, ifdef out specific PPC64
code or use helpers which are available on both PP32 and PPC64

Modify Makefile to always build interrupt.o

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ba073ad67bd971a88ce331b65d6655523b54c794.1612796617.git.christophe.leroy@csgroup.eu
powerpc/syscall: Rename syscall_64.c into interrupt.c 2021-02-11T12:35:10+00:00 Christophe Leroy christophe.leroy@csgroup.eu 2021-02-08T15:10:27+00:00 ab1a517d55b01b54ba70f5d54f926f5ab4b18339 syscall_64.c will be reused almost as is for PPC32. As this file also contains functions to handle other types of interrupts rename it interrupt.c Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/cddc2deaa8f049d3ec419738e69804934919b935.1612796617.git.christophe.leroy@csgroup.eu 
syscall_64.c will be reused almost as is for PPC32.

As this file also contains functions to handle other types
of interrupts rename it interrupt.c

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cddc2deaa8f049d3ec419738e69804934919b935.1612796617.git.christophe.leroy@csgroup.eu
powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o 2021-01-30T11:23:42+00:00 Masahiro Yamada masahiroy@kernel.org 2020-12-23T17:11:41+00:00 bce74491c3008e27dd6e8f79a83b4faa77a08f7e vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not enough to fix the issue. Kbuild is correctly rebuilding it because the command line is changed. PowerPC builds each vdso directory twice; first in vdso_prepare to generate vdso{32,64}-offsets.h, second as part of the ordinary build process to embed vdso{32,64}.so.dbg into the kernel. The problem shows up when CONFIG_PPC_WERROR=y due to the following line in arch/powerpc/Kbuild: subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror In the preparation stage, Kbuild directly visits the vdso directories, hence it does not inherit subdir-ccflags-y. In the second descend, Kbuild adds -Werror, which results in the command line flipping with/without -Werror. It implies a potential danger; if a more critical flag that would impact the resulted vdso, the offsets recorded in the headers might be different from real offsets in the embedded vdso images. Removing the unneeded second descend solves the problem. Reported-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry.fsf@mpe.ellerman.id.au/ Link: https://lore.kernel.org/r/20201223171142.707053-1-masahiroy@kernel.org 
vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not
enough to fix the issue. Kbuild is correctly rebuilding it because the
command line is changed.

PowerPC builds each vdso directory twice; first in vdso_prepare to
generate vdso{32,64}-offsets.h, second as part of the ordinary build
process to embed vdso{32,64}.so.dbg into the kernel.

The problem shows up when CONFIG_PPC_WERROR=y due to the following line
in arch/powerpc/Kbuild:

  subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror

In the preparation stage, Kbuild directly visits the vdso directories,
hence it does not inherit subdir-ccflags-y. In the second descend,
Kbuild adds -Werror, which results in the command line flipping
with/without -Werror.

It implies a potential danger; if a more critical flag that would impact
the resulted vdso, the offsets recorded in the headers might be different
from real offsets in the embedded vdso images.

Removing the unneeded second descend solves the problem.

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry.fsf@mpe.ellerman.id.au/
Link: https://lore.kernel.org/r/20201223171142.707053-1-masahiroy@kernel.org
powerpc: Avoid broken GCC __attribute__((optimize)) 2020-11-19T03:50:14+00:00 Ard Biesheuvel ardb@kernel.org 2020-10-28T08:04:33+00:00 a7223f5bfcaeade4a86d35263493bcda6c940891 Commit 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot") introduced a couple of uses of __attribute__((optimize)) with function scope, to disable the stack protector in some early boot code. Unfortunately, and this is documented in the GCC man pages [0], overriding function attributes for optimization is broken, and is only supported for debug scenarios, not for production: the problem appears to be that setting GCC -f flags using this method will cause it to forget about some or all other optimization settings that have been applied. So the only safe way to disable the stack protector is to disable it for the entire source file. [0] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html Fixes: 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot") Signed-off-by: Ard Biesheuvel <ardb@kernel.org> [mpe: Drop one remaining use of __nostackprotector, reported by snowpatch] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20201028080433.26799-1-ardb@kernel.org 
Commit 7053f80d9696 ("powerpc/64: Prevent stack protection in early
boot") introduced a couple of uses of __attribute__((optimize)) with
function scope, to disable the stack protector in some early boot
code.

Unfortunately, and this is documented in the GCC man pages [0],
overriding function attributes for optimization is broken, and is only
supported for debug scenarios, not for production: the problem appears
to be that setting GCC -f flags using this method will cause it to
forget about some or all other optimization settings that have been
applied.

So the only safe way to disable the stack protector is to disable it
for the entire source file.

[0] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

Fixes: 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[mpe: Drop one remaining use of __nostackprotector, reported by snowpatch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201028080433.26799-1-ardb@kernel.org
powerpc/32s: Rename head_32.S to head_book3s_32.S 2020-10-08T10:17:14+00:00 Christophe Leroy christophe.leroy@csgroup.eu 2020-10-06T09:05:26+00:00 533090e5a980ad80bbe0961b4ed45a9bcf55cc0c Unlike PPC64 which had a single head_64.S, PPC32 are multiple ones. There is the head_32.S, selected by default based on the value of BITS and overridden based on some CONFIG_ values. This leads to thinking that it may be selected by different types of PPC32 platform but indeed it ends up being selected by book3s/32 only. Make that explicit by: - Not doing any default selection based on BITS. - Renaming head_32.S to head_book3s_32.S. - Get head_book3s_32.S selected only by CONFIG_PPC_BOOK3S_32. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> [mpe: Fix head_$(BITS).o reference in arch/powerpc/Makefile] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/319d379f696412681c66a987cc75e6abf8f958d2.1601975100.git.christophe.leroy@csgroup.eu 
Unlike PPC64 which had a single head_64.S, PPC32 are multiple ones.
There is the head_32.S, selected by default based on the value of BITS
and overridden based on some CONFIG_ values. This leads to thinking
that it may be selected by different types of PPC32 platform but
indeed it ends up being selected by book3s/32 only.

Make that explicit by:
- Not doing any default selection based on BITS.
- Renaming head_32.S to head_book3s_32.S.
- Get head_book3s_32.S selected only by CONFIG_PPC_BOOK3S_32.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix head_$(BITS).o reference in arch/powerpc/Makefile]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/319d379f696412681c66a987cc75e6abf8f958d2.1601975100.git.christophe.leroy@csgroup.eu
powerpc/watchpoint: Move DAWR detection logic outside of hw_breakpoint.c 2020-09-15T12:13:19+00:00 Ravi Bangoria ravi.bangoria@linux.ibm.com 2020-09-02T04:29:41+00:00 edc8dd99b29e4d705c45e2a3a6c01b096ee056db Power10 hw has multiple DAWRs but hw doesn't tell which DAWR caused the exception. So we have a sw logic to detect that in hw_breakpoint.c. But hw_breakpoint.c gets compiled only with CONFIG_HAVE_HW_BREAKPOINT=Y. Move DAWR detection logic outside of hw_breakpoint.c so that it can be reused when CONFIG_HAVE_HW_BREAKPOINT is not set. Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200902042945.129369-5-ravi.bangoria@linux.ibm.com 
Power10 hw has multiple DAWRs but hw doesn't tell which DAWR caused
the exception. So we have a sw logic to detect that in hw_breakpoint.c.
But hw_breakpoint.c gets compiled only with CONFIG_HAVE_HW_BREAKPOINT=Y.
Move DAWR detection logic outside of hw_breakpoint.c so that it can be
reused when CONFIG_HAVE_HW_BREAKPOINT is not set.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902042945.129369-5-ravi.bangoria@linux.ibm.com
Merge tag 'kbuild-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild 2020-08-09T21:10:26+00:00 Linus Torvalds torvalds@linux-foundation.org 2020-08-09T21:10:26+00:00 fc80c51fd4b23ec007e88d4c688f2cac1b8648e7 Pull Kbuild updates from Masahiro Yamada: - run the checker (e.g. sparse) after the compiler - remove unneeded cc-option tests for old compiler flags - fix tar-pkg to install dtbs - introduce ccflags-remove-y and asflags-remove-y syntax - allow to trace functions in sub-directories of lib/ - introduce hostprogs-always-y and userprogs-always-y syntax - various Makefile cleanups * tag 'kbuild-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: kbuild: stop filtering out $(GCC_PLUGINS_CFLAGS) from cc-option base kbuild: include scripts/Makefile.* only when relevant CONFIG is enabled kbuild: introduce hostprogs-always-y and userprogs-always-y kbuild: sort hostprogs before passing it to ifneq kbuild: move host .so build rules to scripts/gcc-plugins/Makefile kbuild: Replace HTTP links with HTTPS ones kbuild: trace functions in subdirectories of lib/ kbuild: introduce ccflags-remove-y and asflags-remove-y kbuild: do not export LDFLAGS_vmlinux kbuild: always create directories of targets powerpc/boot: add DTB to 'targets' kbuild: buildtar: add dtbs support kbuild: remove cc-option test of -ffreestanding kbuild: remove cc-option test of -fno-stack-protector Revert "kbuild: Create directory for target DTB" kbuild: run the checker after the compiler 
Pull Kbuild updates from Masahiro Yamada:

 - run the checker (e.g. sparse) after the compiler

 - remove unneeded cc-option tests for old compiler flags

 - fix tar-pkg to install dtbs

 - introduce ccflags-remove-y and asflags-remove-y syntax

 - allow to trace functions in sub-directories of lib/

 - introduce hostprogs-always-y and userprogs-always-y syntax

 - various Makefile cleanups

* tag 'kbuild-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: stop filtering out $(GCC_PLUGINS_CFLAGS) from cc-option base
  kbuild: include scripts/Makefile.* only when relevant CONFIG is enabled
  kbuild: introduce hostprogs-always-y and userprogs-always-y
  kbuild: sort hostprogs before passing it to ifneq
  kbuild: move host .so build rules to scripts/gcc-plugins/Makefile
  kbuild: Replace HTTP links with HTTPS ones
  kbuild: trace functions in subdirectories of lib/
  kbuild: introduce ccflags-remove-y and asflags-remove-y
  kbuild: do not export LDFLAGS_vmlinux
  kbuild: always create directories of targets
  powerpc/boot: add DTB to 'targets'
  kbuild: buildtar: add dtbs support
  kbuild: remove cc-option test of -ffreestanding
  kbuild: remove cc-option test of -fno-stack-protector
  Revert "kbuild: Create directory for target DTB"
  kbuild: run the checker after the compiler
powerpc/pseries: Add KVM guest doorbell restrictions 2020-07-29T11:02:10+00:00 Nicholas Piggin npiggin@gmail.com 2020-07-26T03:51:55+00:00 107c55005fbd5243ee31fb13b6f166cde9e3ade1 KVM guests have certain restrictions and performance quirks when using doorbells. This patch moves the EPAPR KVM guest test so it can be shared with PSERIES, and uses that in doorbell setup code to apply the KVM guest quirks and improves IPI performance for two cases: - PowerVM guests may now use doorbells even if they are secure. - KVM guests no longer use doorbells if XIVE is available. There is a valid complaint that "KVM guest" is not a very reasonable thing to test for, it's preferable for the hypervisor to advertise particular behaviours to the guest so they could change if the hypervisor implementation or configuration changes. However in this case we were already assuming a KVM guest worst case, so this patch is about containing those quirks. If KVM later advertises fast doorbells, we should test for that and override the quirks. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Cédric Le Goater <clg@kaod.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200726035155.1424103-4-npiggin@gmail.com 
KVM guests have certain restrictions and performance quirks when using
doorbells. This patch moves the EPAPR KVM guest test so it can be shared
with PSERIES, and uses that in doorbell setup code to apply the KVM
guest quirks and  improves IPI performance for two cases:

 - PowerVM guests may now use doorbells even if they are secure.

 - KVM guests no longer use doorbells if XIVE is available.

There is a valid complaint that "KVM guest" is not a very reasonable
thing to test for, it's preferable for the hypervisor to advertise
particular behaviours to the guest so they could change if the
hypervisor implementation or configuration changes. However in this case
we were already assuming a KVM guest worst case, so this patch is about
containing those quirks. If KVM later advertises fast doorbells, we
should test for that and override the quirks.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200726035155.1424103-4-npiggin@gmail.com