linux.git/arch/mips/kernel/cps-vec.S, branch v4.13

MIPS: CPS: Handle spurious VP starts more gracefully

2017-06-29T00:42:28+00:00

On pre-r6 systems with the MT ASE the CPS SMP code included checks to
halt the VPE running mips_cps_boot_vpes() if its bit in the struct
core_boot_config vpe_mask field is clear. This was largely done in order
to allow us to start arbitrary VPEs within a core despite the fact that
hardware is typically configured to run only VPE0 after powering up a
core. VPE0 would start the desired other VPEs, halt itself, and the fact
that VPE0 started would be largely hidden & irrelevant.

In MIPSr6 multithreading we have control over which VPs start executing
when a core powers up via the cores CPC registers accessed remotely
through the redirect block. For this reason the MIPSr6 multithreading
path in mips_cps_boot_vpes() hasn't bothered up until now to handle
halting the VP running it.

However it is possible to power up cores entirely in hardware by using a
pwr_up pin associated with the core. Unfortunately some systems wire
this pin to a logic 1, which means that it is possible for a core to
power up at a point that software doesn't expect. The result is that we
generally go execute the kernel on a CPU that ought not to be running &
the results can be unpredictable.

Handle this case by stopping VPs that we don't expect to be running in
mips_cps_boot_vpes() - with this change even if a core powers up it will
do nothing useful & all VPs within it will stop running before they
proceed to run general kernel code & do any damage. Ideally we would
produce some sort of warning here, but given the stage of core bringup
this happens at that would be non-trivial. We also will only hit this if
a core starts up after being offlined via hotplug, and when that happens
we will already produce a warning that the CPU didn't power down in
cps_cpu_die() which seems sufficient.

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16198/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Fix retrieval of VPE mask on big endian CPUs

2017-03-21T19:39:40+00:00

The vpe_mask member of struct core_boot_config is of type atomic_t,
which is a 32bit type. In cps-vec.S this member was being retrieved by a
PTR_L macro, which on 64bit systems is a 64bit load. On little endian
systems this is OK, since the double word that is retrieved will have
the required less significant word in the correct position. However, on
big endian systems the less significant word of the load is retrieved
from address+4, and the more significant from address+0. The destination
register therefore ends up with the required word in the more
significant word
e.g. when starting the second VP of a big endian 64bit system, the load

PTR_L    ta2, COREBOOTCFG_VPEMASK(a0)

ends up setting register ta2 to 0x0000000300000000

When this value is written to the CPC it is ignored, since it is
invalid to write anything larger than 4 bits. This results in any VP
other than VP0 in a core failing to start in 64bit big endian systems.

Change the load to a 32bit load word instruction to fix the bug.

Fixes: f12401d7219f ("MIPS: smp-cps: Pull boot config retrieval out of mips_cps_boot_vpes")
Signed-off-by: Matt Redfearn 
Cc: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15787/
Signed-off-by: Ralf Baechle

MIPS: CPS: Copy EVA configuration when starting secondary VPs.

2016-05-28T10:35:05+00:00

When starting secondary VPEs which support EVA and the SegCtl registers,
copy the memory segmentation configuration from the running VPE to ensure
that all VPEs in the core have a consistent virtual memory map.

The EVA configuration of secondary cores is dealt with when starting the
core via the CM.

Signed-off-by: Matt Redfearn 
Cc: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13291/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Stop printing EJTAG exceptions to UART

2016-05-13T12:01:51+00:00

When CONFIG_MIPS_CPS_NS16550 is enabled, some register state is dumped
to the UART when an exception is taken via the BEV on secondary cores.
EJTAG exceptions are architecturally expected to be handled by the BEV
even when Status.BEV is 0. This effectively means that if userland
executes an sdbbp instruction on a secondary core then the kernel dumps
register state to the UART even though the exception is perfectly normal
& expected. Prevent this by simply not dumping information to the UART
for EJTAG exceptions.

Fixes: 609cf6f2291a ("MIPS: CPS: Early debug using an ns16550-compatible UART")
Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12341/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Support MIPSr6 Virtual Processors

2016-05-13T12:01:50+00:00

Introduce support for bringing up Virtual Processors in MIPSr6 systems
as CPUs, much like their VPE parallel from the now-deprecated MT ASE.
The existing mips_cps_boot_vpes function fits the MIPSr6 architecture
pretty well - it can now simply write the mask of running VPs to the
VC_RUN register, rather than looping through each & starting or stopping
as appropriate as is done for VPEs from the MT ASE. Thus the VP support
is in general an extension & simplification of the existing MT ASE VPE
(aka SMVP) support.

Signed-off-by: Paul Burton 
Cc: Matt Redfearn 
Cc: Rusty Russell 
Cc: Maciej W. Rozycki 
Cc: Niklas Cassel 
Cc: Ezequiel Garcia 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12339/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Skip core setup if coherent

2016-05-13T12:01:50+00:00

In preparation for supporting MIPSr6 multithreading (ie. VPs) which will
begin execution from the core reset vector, skip core level setup if the
core is already coherent. This is never the case when a core is first
started, since boot_core explicitly clears the cores GCR_Cx_COH_EN
register, and always the case when secondary VPs start since the first
VP to start will have enabled coherence after initialising the core &
its caches.

One notable side effect of this patch is that eva_init gets called
slightly earlier, prior to mips_cps_core_init rather than after it.

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12338/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Pull boot config retrieval out of mips_cps_boot_vpes

2016-05-13T12:01:50+00:00

The mips_cps_boot_vpes function previously included code to retrieve
pointers to the core & VPE boot configuration structs. These structures
were used both by mips_cps_boot_vpes and by its mips_cps_core_entry
callsite. In preparation for skipping the call to mips_cps_boot_vpes on
some invocations of mips_cps_core_entry, pull the calculation of those
pointers out into a separate function such that it can continue to be
shared.

Signed-off-by: Paul Burton 
Cc: Rusty Russell 
Cc: Matt Redfearn 
Cc: Niklas Cassel 
Cc: Ezequiel Garcia 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12337/
Signed-off-by: Ralf Baechle

MIPS: smp-cps: Pull cache init into a function

2016-05-13T12:01:49+00:00

In preparation for further modifications to mips_cps_core_entry, pull
the L1 cache initialisation out into a separate function. This both
makes the code in mips_cps_core_entry read more clearly, particularly
when modifying it, and shortens it which will become important as code
is added that needs to continue to fit within the reset vector.

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12336/
Signed-off-by: Ralf Baechle

MIPS: CPS: drop .set mips64r2 directives

2015-12-22T11:16:32+00:00

Commit 977e043d5ea1 ("MIPS: kernel: cps-vec: Replace mips32r2 ISA level
with mips64r2") leads to .set mips64r2 directives being present in 32
bit (ie. CONFIG_32BIT=y) kernels. This is incorrect & leads to MIPS64
instructions being emitted by the assembler when expanding
pseudo-instructions. For example the "move" instruction can legitimately
be expanded to a "daddu". This causes problems when the kernel is run on
a MIPS32 CPU, as CONFIG_32BIT kernels of course often are...

Fix this by dropping the .set  directives entirely now that Kconfig
should be ensuring that kernels including this code are built with a
suitable -march= compiler flag.

Signed-off-by: Paul Burton 
Cc: Markos Chandras 
Cc: James Hogan 
Cc:  # 3.16+
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/10869/
Signed-off-by: Ralf Baechle

MIPS: CPS: Skip Config1 presence check

2015-11-11T07:35:05+00:00

The Config1 register is architecturally defined as required, and is thus
present in all systems which may make use of cps-vec.S. Skip the check
for its presence via the Config.M bit.

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Markos Chandras 
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11204/
Signed-off-by: Ralf Baechle