[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Alexey Brodkin]

Modern ARC cores (those sporting MMU of version 3 and 4) allow selection
of different page sizes (4, 8 or 16 kB) during ASIC design creation.
And it's important to build a toolchain with page size setting that matches
hardware.

Otherwise user-space applications will fail on execution due to
unexpected data layout/alignment etc.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
c: Anton Kolesov <akolesov@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
 arch/Config.in.arc       | 30 ++++++++++++++++++++++++++++++
 package/uclibc/uclibc.mk |  8 ++++++++
 2 files changed, 38 insertions(+)

diff --git a/arch/Config.in.arc b/arch/Config.in.arc
index b48a90f..e960eb8 100644
--- a/arch/Config.in.arc
+++ b/arch/Config.in.arc
@@ -40,3 +40,33 @@ config BR2_GCC_TARGET_CPU
 	default "arc700" if BR2_arc750d
 	default "arc700" if BR2_arc770d
 	default "archs"	 if BR2_archs38
+
+choice
+	prompt "MMU Page Size"
+	default BR2_arc_page_size_8k
+	help
+	    MMU starting from version 3 (could be found in ARC 770) and now
+	    version 4 (could be found in ARC HS38) allows selection of page
+	    size during ASIC design creation. And it's important to build
+	    a toolchain with page size setting that matches hardware.
+	    Otherwise user-space applications will fail on execution due to
+	    unexpected data layout/alignment.
+
+config BR2_arc_page_size_4k
+	bool "4KB"
+	depends on BR2_arc770d || BR2_archs38
+
+config BR2_arc_page_size_8k
+	bool "8KB"
+
+config BR2_arc_page_size_16k
+	bool "16KB"
+	depends on BR2_arc770d || BR2_archs38
+
+endchoice
+
+config BR2_ARC_PAGE_SIZE
+	string
+	default "4K" if BR2_arc_page_size_4k
+	default "8K" if BR2_arc_page_size_8k
+	default "16K" if BR2_arc_page_size_16k
diff --git a/package/uclibc/uclibc.mk b/package/uclibc/uclibc.mk
index 9dfafad..a2ba230 100644
--- a/package/uclibc/uclibc.mk
+++ b/package/uclibc/uclibc.mk
@@ -70,6 +70,13 @@ UCLIBC_ARC_TYPE = CONFIG_$(call qstrip,$(BR2_UCLIBC_ARC_TYPE))
 define UCLIBC_ARC_TYPE_CONFIG
 	$(call KCONFIG_ENABLE_OPT,$(UCLIBC_ARC_TYPE),$(@D)/.config)
 endef
+
+UCLIBC_ARC_PAGE_SIZE = CONFIG_ARC_PAGE_SIZE_$(call qstrip,$(BR2_ARC_PAGE_SIZE))
+define UCLIBC_ARC_PAGE_SIZE_CONFIG
+	$(SED) '/CONFIG_ARC_PAGE_SIZE_*/d' $(@D)/.config
+	$(call KCONFIG_ENABLE_OPT,$(UCLIBC_ARC_PAGE_SIZE),$(@D)/.config)
+endef
+
 endif # arc
 
 #
@@ -367,6 +374,7 @@ define UCLIBC_KCONFIG_FIXUP_CMDS
 	$(call KCONFIG_SET_OPT,SHARED_LIB_LOADER_PREFIX,"/lib",$(@D)/.config)
 	$(UCLIBC_MMU_CONFIG)
 	$(UCLIBC_ARC_TYPE_CONFIG)
+	$(UCLIBC_ARC_PAGE_SIZE_CONFIG)
 	$(UCLIBC_ARM_ABI_CONFIG)
 	$(UCLIBC_ARM_BX_CONFIG)
 	$(UCLIBC_MIPS_ABI_CONFIG)
-- 
2.4.3

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Thomas Petazzoni]

Dear Alexey Brodkin,

On Thu, 16 Jul 2015 22:04:01 +0300, Alexey Brodkin wrote:

> +choice
> +	prompt "MMU Page Size"
> +	default BR2_arc_page_size_8k
> +	help
> +	    MMU starting from version 3 (could be found in ARC 770) and now
> +	    version 4 (could be found in ARC HS38) allows selection of page
> +	    size during ASIC design creation. And it's important to build

Remove the "And".

> +	    a toolchain with page size setting that matches hardware.

"with a page size matching the hardware configuration"

> +	    Otherwise user-space applications will fail on execution due to

"will fail at runtime"

> +	    unexpected data layout/alignment.

What is the impact for people using external toolchains?

> +
> +config BR2_arc_page_size_4k

Can you use BR2_ARC_PAGE_SIZE_4K instead? I know the BR2_arc option is
lower-case, but for most architectures options are upper-case, even if
the core selection is lower-case. I think lower-case options is more an
accident of the past rather than a real policy.

> +	bool "4KB"
> +	depends on BR2_arc770d || BR2_archs38
> +
> +config BR2_arc_page_size_8k
> +	bool "8KB"
> +
> +config BR2_arc_page_size_16k
> +	bool "16KB"
> +	depends on BR2_arc770d || BR2_archs38

Can you quickly comment on why 4 KB / 16 KB have dependencies on
specific ARC cores and not 8 KB ?

Can you respin with those changes?

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Arnout Vandecappelle]

On 07/16/15 21:04, Alexey Brodkin wrote:
> Modern ARC cores (those sporting MMU of version 3 and 4) allow selection
> of different page sizes (4, 8 or 16 kB) during ASIC design creation.
> And it's important to build a toolchain with page size setting that matches
> hardware.
> 
> Otherwise user-space applications will fail on execution due to
> unexpected data layout/alignment etc.
> 
> Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
> c: Anton Kolesov <akolesov@synopsys.com>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> ---
>  arch/Config.in.arc       | 30 ++++++++++++++++++++++++++++++
>  package/uclibc/uclibc.mk |  8 ++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/arch/Config.in.arc b/arch/Config.in.arc
> index b48a90f..e960eb8 100644
> --- a/arch/Config.in.arc
> +++ b/arch/Config.in.arc
> @@ -40,3 +40,33 @@ config BR2_GCC_TARGET_CPU
>  	default "arc700" if BR2_arc750d
>  	default "arc700" if BR2_arc770d
>  	default "archs"	 if BR2_archs38
> +
> +choice
> +	prompt "MMU Page Size"

 It is not really current policy, but wouldn't it make more sense to do

	prompt "MMU Page Size" if BR2_arc770d || BR2_archs38

? (i.e., only show it when there's anything to choose).

 Also perhaps it makes sense to add a new symbol
BR2_ARC_SUPPORTS_PAGE_SIZE_SELECTION or similar instead of specifying the
individual processors.


 Regards,
 Arnout

> +	default BR2_arc_page_size_8k
> +	help
> +	    MMU starting from version 3 (could be found in ARC 770) and now
> +	    version 4 (could be found in ARC HS38) allows selection of page
> +	    size during ASIC design creation. And it's important to build
> +	    a toolchain with page size setting that matches hardware.
> +	    Otherwise user-space applications will fail on execution due to
> +	    unexpected data layout/alignment.
> +
> +config BR2_arc_page_size_4k
> +	bool "4KB"
> +	depends on BR2_arc770d || BR2_archs38
> +
> +config BR2_arc_page_size_8k
> +	bool "8KB"
> +
> +config BR2_arc_page_size_16k
> +	bool "16KB"
> +	depends on BR2_arc770d || BR2_archs38

[snip]


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Thomas Petazzoni]

Arnout,

On Fri, 17 Jul 2015 00:40:20 +0200, Arnout Vandecappelle wrote:

> > +choice
> > +	prompt "MMU Page Size"
> 
>  It is not really current policy, but wouldn't it make more sense to do
> 
> 	prompt "MMU Page Size" if BR2_arc770d || BR2_archs38

Why? In the patch submitted by Alexey, the 8K option is available for
all cores.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Alexey Brodkin]

Hi Thomas, Arnout,

On Fri, 2015-07-17 at 09:59 +0200, Thomas Petazzoni wrote:
> Arnout,
> 
> On Fri, 17 Jul 2015 00:40:20 +0200, Arnout Vandecappelle wrote:
> 
> > > +choice
> > > +	prompt "MMU Page Size"
> > 
> >  It is not really current policy, but wouldn't it make more sense to do
> > 
> > 	prompt "MMU Page Size" if BR2_arc770d || BR2_archs38
> 
> Why? In the patch submitted by Alexey, the 8K option is available for
> all cores.

Indeed there's no reason to select page size for MMUv2 (read ARC 750D), but
IMHO it's good to let user know what's current page size.

Because software built for ARC 750D will run perfectly fine on ARC770D
if it has the same page size (and by default it is 8k).

That's why I decided to leave a "Page Size" entry in configuration utility
even though it could not be modified for ARC 750D.

-Alexey

[Buildroot] [PATCH] ARC: allow selection of MMU page size

[Alexey Brodkin]

Hi Thomas,

On Thu, 2015-07-16 at 23:25 +0200, Thomas Petazzoni wrote:
> Dear Alexey Brodkin,
> 
> On Thu, 16 Jul 2015 22:04:01 +0300, Alexey Brodkin wrote:
> 
> > +choice
> > +	prompt "MMU Page Size"
> > +	default BR2_arc_page_size_8k
> > +	help
> > +	    MMU starting from version 3 (could be found in ARC 770) and now
> > +	    version 4 (could be found in ARC HS38) allows selection of page
> > +	    size during ASIC design creation. And it's important to build
> 
> Remove the "And".
> 
> > +	    a toolchain with page size setting that matches hardware.
> 
> "with a page size matching the hardware configuration"
> 
> > +	    Otherwise user-space applications will fail on execution due to
> 
> "will fail at runtime"

Thanks for pointing to that.

> > +	    unexpected data layout/alignment.
> 
> What is the impact for people using external toolchains?

Well people have to use toolchain which page size matches HW.
That means you need to know which value is set in both
toolchain and HW.

By default in either substances 8k is used and most of the time
people will use it.

Still even in case of external toolchain we nay check for PAGE_SHIFT
value in "sysroot/usr/include/bits/uClibc_page.h".

PAGE_SHIFT=12 -> PAGE_SIZE=4k
PAGE_SHIFT=13 -> PAGE_SIZE=8k (default)
PAGE_SHIFT=14 -> PAGE_SIZE=16k

> > +
> > +config BR2_arc_page_size_4k
> 
> Can you use BR2_ARC_PAGE_SIZE_4K instead? I know the BR2_arc option is
> lower-case, but for most architectures options are upper-case, even if
> the core selection is lower-case. I think lower-case options is more an
> accident of the past rather than a real policy.

OK, will do.

> > +	bool "4KB"
> > +	depends on BR2_arc770d || BR2_archs38
> > +
> > +config BR2_arc_page_size_8k
> > +	bool "8KB"
> > +
> > +config BR2_arc_page_size_16k
> > +	bool "16KB"
> > +	depends on BR2_arc770d || BR2_archs38
> 
> Can you quickly comment on why 4 KB / 16 KB have dependencies on
> specific ARC cores and not 8 KB ?

8K page was the only option on earlier ARC cores like ARC 750D.
Starting from ARC 770D it's possible to select page size from 3 options:
4, 8 and 16k. But still 8k is its default value and most often that's
what people use.

Do you want that comment

> Can you respin with those changes?

Sure, will do shortly.\

-Alexey