[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Florian Fainelli]

Cortex-A9 on at least BCM4708 SoCs are not LPAE capable, booting such a
kernel will result in the following:

Error: Kernel with LPAE support, but CPU does not support LPAE.

Restrict such SoCs to be built in a configuration that does not enable
ARM_LPAE.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 arch/arm/mach-bcm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/mach-bcm/Kconfig b/arch/arm/mach-bcm/Kconfig
index 0ac9e4b3b265..153a660da004 100644
--- a/arch/arm/mach-bcm/Kconfig
+++ b/arch/arm/mach-bcm/Kconfig
@@ -38,6 +38,7 @@ config ARCH_BCM_CYGNUS
 config ARCH_BCM_5301X
 	bool "Broadcom BCM470X / BCM5301X ARM SoC" if ARCH_MULTI_V7
 	select ARCH_BCM_IPROC
+	depends on !ARM_LPAE
 	help
 	  Support for Broadcom BCM470X and BCM5301X SoCs with ARM CPU cores.
 
-- 
2.1.0

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Arnd Bergmann]

On Tuesday 14 July 2015 11:12:15 Florian Fainelli wrote:
> Cortex-A9 on at least BCM4708 SoCs are not LPAE capable, booting such a
> kernel will result in the following:
> 
> Error: Kernel with LPAE support, but CPU does not support LPAE.
> 
> Restrict such SoCs to be built in a configuration that does not enable
> ARM_LPAE.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> 

This is an old problem for all platforms, I think we want a more
generic solution though, instead of adding the !LPAE dependency
for each Cortex-A5/8/9 platform.

	Arnd

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Florian Fainelli]

On 14/07/15 13:43, Arnd Bergmann wrote:
> On Tuesday 14 July 2015 11:12:15 Florian Fainelli wrote:
>> Cortex-A9 on at least BCM4708 SoCs are not LPAE capable, booting such a
>> kernel will result in the following:
>>
>> Error: Kernel with LPAE support, but CPU does not support LPAE.
>>
>> Restrict such SoCs to be built in a configuration that does not enable
>> ARM_LPAE.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>>
> 
> This is an old problem for all platforms, I think we want a more
> generic solution though, instead of adding the !LPAE dependency
> for each Cortex-A5/8/9 platform.

Fair enough, what do you have in mind? Should we introduce something
like CONFIG_V7_A9 and such, and update all platforms to select such
symbols such that we can then apply a restriction on other symbols if
there needs to be?

What if any of these CPUs end-up supporting LPAE, but this cannot be
flagged at build time?
-- 
Florian

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Arnd Bergmann]

On Tuesday 14 July 2015 14:29:31 Florian Fainelli wrote:
> On 14/07/15 13:43, Arnd Bergmann wrote:
> > On Tuesday 14 July 2015 11:12:15 Florian Fainelli wrote:
> >> Cortex-A9 on at least BCM4708 SoCs are not LPAE capable, booting such a
> >> kernel will result in the following:
> >>
> >> Error: Kernel with LPAE support, but CPU does not support LPAE.
> >>
> >> Restrict such SoCs to be built in a configuration that does not enable
> >> ARM_LPAE.
> >>
> >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> >>
> > 
> > This is an old problem for all platforms, I think we want a more
> > generic solution though, instead of adding the !LPAE dependency
> > for each Cortex-A5/8/9 platform.
> 
> Fair enough, what do you have in mind? Should we introduce something
> like CONFIG_V7_A9 and such, and update all platforms to select such
> symbols such that we can then apply a restriction on other symbols if
> there needs to be?
> 
> What if any of these CPUs end-up supporting LPAE, but this cannot be
> flagged at build time?

I would introduce special architecture levels for ARMv7+LPAE and/or
ARMv7VE. I am not entirely sure what combinations exist and whether
it's enough to add ARMv7VE.

Basically, I think ARM_LPAE should only be selectable if ARMv7VE
is the lowest architecture level that is enabled, and all ARMv7VE
based platforms would have to be changed to depend on ARCH_MULTI_V7VE
instead of ARCH_MULTI_V7.

Also, when building an ARMv7VE kernel, we really want to build with
gcc -march=armv7ve (as long as that is available, possibly falling
back to -mcpu=cortex-a15), so we build with the idiv instructions.
The part I'm unclear about is whether there are CPU cores that support
only idiv but not LPAE or vice versa. If there are, we need an extra
level.

	Arnd

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Florian Fainelli]

On 15/07/15 03:08, Arnd Bergmann wrote:
> On Tuesday 14 July 2015 14:29:31 Florian Fainelli wrote:
>> On 14/07/15 13:43, Arnd Bergmann wrote:
>>> On Tuesday 14 July 2015 11:12:15 Florian Fainelli wrote:
>>>> Cortex-A9 on at least BCM4708 SoCs are not LPAE capable, booting such a
>>>> kernel will result in the following:
>>>>
>>>> Error: Kernel with LPAE support, but CPU does not support LPAE.
>>>>
>>>> Restrict such SoCs to be built in a configuration that does not enable
>>>> ARM_LPAE.
>>>>
>>>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>>>>
>>>
>>> This is an old problem for all platforms, I think we want a more
>>> generic solution though, instead of adding the !LPAE dependency
>>> for each Cortex-A5/8/9 platform.
>>
>> Fair enough, what do you have in mind? Should we introduce something
>> like CONFIG_V7_A9 and such, and update all platforms to select such
>> symbols such that we can then apply a restriction on other symbols if
>> there needs to be?
>>
>> What if any of these CPUs end-up supporting LPAE, but this cannot be
>> flagged at build time?
> 
> I would introduce special architecture levels for ARMv7+LPAE and/or
> ARMv7VE. I am not entirely sure what combinations exist and whether
> it's enough to add ARMv7VE.
> 
> Basically, I think ARM_LPAE should only be selectable if ARMv7VE
> is the lowest architecture level that is enabled, and all ARMv7VE
> based platforms would have to be changed to depend on ARCH_MULTI_V7VE
> instead of ARCH_MULTI_V7.
> 
> Also, when building an ARMv7VE kernel, we really want to build with
> gcc -march=armv7ve (as long as that is available, possibly falling
> back to -mcpu=cortex-a15), so we build with the idiv instructions.
> The part I'm unclear about is whether there are CPU cores that support
> only idiv but not LPAE or vice versa. If there are, we need an extra
> level.

I like the idea in general, but I think this is going to be a very
tedious job to collect every single CR values for ARMv7 processors to
determine whether they are pure v7 or v7e... Maybe we could use
kernelci.org to start extracting the relevant lines in bootlogs and
people can start adding their own chips one by one?
-- 
Florian

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Arnd Bergmann]

On Wednesday 15 July 2015 09:38:52 Florian Fainelli wrote:
> 
> I like the idea in general, but I think this is going to be a very
> tedious job to collect every single CR values for ARMv7 processors to
> determine whether they are pure v7 or v7e... Maybe we could use
> kernelci.org to start extracting the relevant lines in bootlogs and
> people can start adding their own chips one by one?

No, we know most of them:

Cortex-A5, A8, A9: ARMv7, no LPAE, no IDIV
Cortex-A7, A15, A12, A17: ARMv7VE, no LPAE, no IDIV


Almost everyone uses the above cores unmodified.

The ones I'm not 100% sure about are:

Marvell PJ4 (almost certainly ARMv7)
Marvell PJ4B (probably ARMv7 plus IDIV without LPAE)
Qualcomm Scorpion (probably ARMv7)
Qualcomm Krait (probably ARMv7 plus IDIV without LPAE)
Broadcom Brahma-B15 (almost certainly ARMv7VE)

We basically just need to find out from the mach-qcom and
mach-mvebu maintainers what combination of LPAE and IDIV
they need to support, and you can find out about B15.

If my list above is correct, there are no CPUs that have
LPAE but don't have IDIV, and we just need to decide how
to represent that.

	Arnd

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Gregory Fong]

On Wed, Jul 15, 2015 at 1:41 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 15 July 2015 09:38:52 Florian Fainelli wrote:
>>
>> I like the idea in general, but I think this is going to be a very
>> tedious job to collect every single CR values for ARMv7 processors to
>> determine whether they are pure v7 or v7e... Maybe we could use
>> kernelci.org to start extracting the relevant lines in bootlogs and
>> people can start adding their own chips one by one?
>
> No, we know most of them:
>
> Cortex-A5, A8, A9: ARMv7, no LPAE, no IDIV
> Cortex-A7, A15, A12, A17: ARMv7VE, no LPAE, no IDIV
>
>
> Almost everyone uses the above cores unmodified.
>
> The ones I'm not 100% sure about are:
>
> [...]
> Broadcom Brahma-B15 (almost certainly ARMv7VE)

Confirmed, B15 is ARMv7VE.

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Russell King - ARM Linux]

On Wed, Jul 15, 2015 at 10:41:51PM +0200, Arnd Bergmann wrote:
> On Wednesday 15 July 2015 09:38:52 Florian Fainelli wrote:
> > 
> > I like the idea in general, but I think this is going to be a very
> > tedious job to collect every single CR values for ARMv7 processors to
> > determine whether they are pure v7 or v7e... Maybe we could use
> > kernelci.org to start extracting the relevant lines in bootlogs and
> > people can start adding their own chips one by one?
> 
> No, we know most of them:
> 
> Cortex-A5, A8, A9: ARMv7, no LPAE, no IDIV
> Cortex-A7, A15, A12, A17: ARMv7VE, no LPAE, no IDIV
> 
> 
> Almost everyone uses the above cores unmodified.
> 
> The ones I'm not 100% sure about are:
> 
> Marvell PJ4 (almost certainly ARMv7)
> Marvell PJ4B (probably ARMv7 plus IDIV without LPAE)

Dove (PJ4B iirc):

Features        : half thumb fastmult vfp edsp iwmmxt thumbee vfpv3
		  vfpv3d16 tls idivt

So, thumb-only idiv, no LPAE.

> If my list above is correct, there are no CPUs that have
> LPAE but don't have IDIV, and we just need to decide how
> to represent that.

GCC ARMv7VE selects ARM idiv and Thumb idiv support, so you need to
check for idiva and idivt support from the CPU, otherwise we're into
even more Kconfig dependency hell trying to work out the dependencies
for T2 kernel builds vs ARM kernel builds.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.

[PATCH] ARM: BCM: Restrict Broadcom BCM470X / BCM5301X to non-LPAE

[Arnd Bergmann]

On Wednesday 15 July 2015 22:00:44 Russell King - ARM Linux wrote:
> On Wed, Jul 15, 2015 at 10:41:51PM +0200, Arnd Bergmann wrote:
> > On Wednesday 15 July 2015 09:38:52 Florian Fainelli wrote:
> > > 
> > > I like the idea in general, but I think this is going to be a very
> > > tedious job to collect every single CR values for ARMv7 processors to
> > > determine whether they are pure v7 or v7e... Maybe we could use
> > > kernelci.org to start extracting the relevant lines in bootlogs and
> > > people can start adding their own chips one by one?
> > 
> > No, we know most of them:
> > 
> > Cortex-A5, A8, A9: ARMv7, no LPAE, no IDIV
> > Cortex-A7, A15, A12, A17: ARMv7VE, no LPAE, no IDIV
> > 
> > 
> > Almost everyone uses the above cores unmodified.
> > 
> > The ones I'm not 100% sure about are:
> > 
> > Marvell PJ4 (almost certainly ARMv7)
> > Marvell PJ4B (probably ARMv7 plus IDIV without LPAE)
> 
> Dove (PJ4B iirc):
> 
> Features        : half thumb fastmult vfp edsp iwmmxt thumbee vfpv3
> 		  vfpv3d16 tls idivt
> 
> So, thumb-only idiv, no LPAE.

Oh, so potentially another level.

> > If my list above is correct, there are no CPUs that have
> > LPAE but don't have IDIV, and we just need to decide how
> > to represent that.
> 
> GCC ARMv7VE selects ARM idiv and Thumb idiv support, so you need to
> check for idiva and idivt support from the CPU, otherwise we're into
> even more Kconfig dependency hell trying to work out the dependencies
> for T2 kernel builds vs ARM kernel builds.

An easy way out of course would be to ignore the idivt capability of
PJ4B and always treat it as ARMv7 even when building a thumb2 based
kernel.

The ARCH_MULTI_V* cpu level configuration we currently have is
indeed too complicated already, and I've tried to come up with
a way to simplify it.

The best idea I've had so far is to just use the global setting
for picking the minimum level, and working out the supported platforms
and features from there. Something along the lines of

choice
	prompt "Minimum CPU Architecture level"

config ARM_MIN_V4
	bool "ARMv4 based platforms (FA526)"
	select ARCH_MULTI_V4
	select ARCH_MULTI_V4T
	select ARCH_MULTI_V5

...

config ARM_MIN_V6
	bool "ARMv6 based platforms (ARM1136r0)"
	select ARCH_MULTI_V6
	select ARCH_MULTI_V6K
	select ARCH_MULTI_V7
	select ARCH_MULTI_V7_IDIVT
	select ARCH_MULTI_V7_IDIV
	select ARCH_MULTI_V7VE # for lpae
	select ARCH_MULTI_V8 # for crypto, maybe same as v7ve?

...

config ARM_MIN_V7_IDIV
	bool "ARMv7 based platforms with integer divide"
	select ARCH_MULTI_V7_IDIV
	select ARCH_MULTI_V7VE
	select ARCH_MULTI_V8
...

endchoice

I think this would be able to cover all cases we are
interested in, including future extensions. The main problem
I couldn't solve is how to convert existing defconfigs and
user configuration files without relying on users to pick
the right option.

	Arnd