[U-Boot] [PATCH v3] armv8: caches: Added routine to set non cacheable region

[U-Boot] [PATCH v3] armv8: caches: Added routine to set non cacheable region

[Siva Durga Prasad Paladugu]

Added routine mmu_set_region_dcache_behaviour() to set a
particular region as non cacheable.

Define dummy routine for mmu_set_region_dcache_behaviour()
to handle incase of dcache off.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
---
Changes in v3:
- Removed board depenedency to calculate the page table
  address to start with looking into the entry. Now, get
  the page table address from the board specific code.
- Updated flush dcache with actual Page address instead
  of MMU entry.
Changes in v2:
- Fix patch subject (remove addional zzz from v1)
- Remove armv8: caches: Disable dcache after flush patch from this
  series based on the talk with Mark Rutland (patch is not needed
  anymore)
---
 arch/arm/cpu/armv8/cache_v8.c |   32 ++++++++++++++++++++++++++++++++
 arch/arm/include/asm/system.h |   29 +++++++++++++++++++----------
 2 files changed, 51 insertions(+), 10 deletions(-)

diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
index c5ec529..1c6b4b4 100644
--- a/arch/arm/cpu/armv8/cache_v8.c
+++ b/arch/arm/cpu/armv8/cache_v8.c
@@ -139,6 +139,33 @@ int dcache_status(void)
 	return (get_sctlr() & CR_C) != 0;
 }
 
+u64 *__weak arch_get_page_table(void) {
+	puts("No page table offset defined\n");
+
+	return NULL;
+}
+
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option)
+{
+	u64 *page_table = arch_get_page_table();
+	u64 upto, end;
+
+	if (page_table == NULL)
+		return;
+
+	end = ALIGN(start + size, (1 << MMU_SECTION_SHIFT)) >>
+	      MMU_SECTION_SHIFT;
+	start = start >> MMU_SECTION_SHIFT;
+	for (upto = start; upto < end; upto++) {
+		page_table[upto] &= ~PMD_ATTRINDX_MASK;
+		page_table[upto] |= PMD_ATTRINDX(option);
+	}
+
+	start = start << MMU_SECTION_SHIFT;
+	end = end << MMU_SECTION_SHIFT;
+	flush_dcache_range(start, end);
+}
 #else	/* CONFIG_SYS_DCACHE_OFF */
 
 void invalidate_dcache_all(void)
@@ -170,6 +197,11 @@ int dcache_status(void)
 	return 0;
 }
 
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option)
+{
+}
+
 #endif	/* CONFIG_SYS_DCACHE_OFF */
 
 #ifndef CONFIG_SYS_ICACHE_OFF
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index 760e8ab..868ea54 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -15,9 +15,15 @@
 #define CR_EE		(1 << 25)	/* Exception (Big) Endian	*/
 
 #define PGTABLE_SIZE	(0x10000)
+/* 2MB granularity */
+#define MMU_SECTION_SHIFT	21
 
 #ifndef __ASSEMBLY__
 
+enum dcache_option {
+	DCACHE_OFF = 0x3,
+};
+
 #define isb()				\
 	({asm volatile(			\
 	"isb" : : : "memory");		\
@@ -265,16 +271,6 @@ enum {
 #endif
 
 /**
- * Change the cache settings for a region.
- *
- * \param start		start address of memory region to change
- * \param size		size of memory region to change
- * \param option	dcache option to select
- */
-void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
-				     enum dcache_option option);
-
-/**
  * Register an update to the page tables, and flush the TLB
  *
  * \param start		start address of update in page table
@@ -295,4 +291,17 @@ phys_addr_t noncached_alloc(size_t size, size_t align);
 
 #endif /* CONFIG_ARM64 */
 
+#ifndef __ASSEMBLY__
+/**
+ * Change the cache settings for a region.
+ *
+ * \param start		start address of memory region to change
+ * \param size		size of memory region to change
+ * \param option	dcache option to select
+ */
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option);
+
+#endif /* __ASSEMBLY__ */
+
 #endif
-- 
1.7.1

[U-Boot] [PATCH v3] armv8: caches: Added routine to set non cacheable region

[Mark Rutland]

Hi,

> +void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
> +				     enum dcache_option option)
> +{
> +	u64 *page_table = arch_get_page_table();
> +	u64 upto, end;
> +
> +	if (page_table == NULL)
> +		return;
> +
> +	end = ALIGN(start + size, (1 << MMU_SECTION_SHIFT)) >>
> +	      MMU_SECTION_SHIFT;
> +	start = start >> MMU_SECTION_SHIFT;
> +	for (upto = start; upto < end; upto++) {
> +		page_table[upto] &= ~PMD_ATTRINDX_MASK;
> +		page_table[upto] |= PMD_ATTRINDX(option);
> +	}

These writes might not be visible to the page table walkers immediately,
and the TLBs might still contain stale values for a while afterwards.
That could render the cache maintenance useless (as speculative fetches
could still occur due to cacheable attributes still being in place).

You need a DSB to ensure writes are visible to the page table walkers
(with a compiler barrier to ensure that the writes actually occur before
the DSB), and some TLB maintenance (complete with another DSB) to ensure
that the TLBs don't contain stale values by the time to get to the cache
afterwards.

Also minor nit, but s/upto/i/?

> +
> +	start = start << MMU_SECTION_SHIFT;
> +	end = end << MMU_SECTION_SHIFT;
> +	flush_dcache_range(start, end);
> +}
>  #else	/* CONFIG_SYS_DCACHE_OFF */
>  
>  void invalidate_dcache_all(void)
> @@ -170,6 +197,11 @@ int dcache_status(void)
>  	return 0;
>  }
>  
> +void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
> +				     enum dcache_option option)
> +{
> +}
> +
>  #endif	/* CONFIG_SYS_DCACHE_OFF */
>  
>  #ifndef CONFIG_SYS_ICACHE_OFF
> diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
> index 760e8ab..868ea54 100644
> --- a/arch/arm/include/asm/system.h
> +++ b/arch/arm/include/asm/system.h
> @@ -15,9 +15,15 @@
>  #define CR_EE		(1 << 25)	/* Exception (Big) Endian	*/
>  
>  #define PGTABLE_SIZE	(0x10000)
> +/* 2MB granularity */
> +#define MMU_SECTION_SHIFT	21

Do we only expect 4K pages for now?

Thanks,
Mark.

[U-Boot] [PATCH v3] armv8: caches: Added routine to set non cacheable region

[Siva Durga Prasad Paladugu]

Hi Mark,

> -----Original Message-----
> From: Mark Rutland [mailto:mark.rutland at arm.com]
> Sent: Thursday, May 28, 2015 3:10 PM
> To: Siva Durga Prasad Paladugu
> Cc: u-boot at lists.denx.de; Michal Simek; Siva Durga Prasad Paladugu
> Subject: Re: [PATCH v3] armv8: caches: Added routine to set non cacheable
> region
>
> Hi,
>
> > +void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
> > +                                enum dcache_option option)
> > +{
> > +   u64 *page_table = arch_get_page_table();
> > +   u64 upto, end;
> > +
> > +   if (page_table == NULL)
> > +           return;
> > +
> > +   end = ALIGN(start + size, (1 << MMU_SECTION_SHIFT)) >>
> > +         MMU_SECTION_SHIFT;
> > +   start = start >> MMU_SECTION_SHIFT;
> > +   for (upto = start; upto < end; upto++) {
> > +           page_table[upto] &= ~PMD_ATTRINDX_MASK;
> > +           page_table[upto] |= PMD_ATTRINDX(option);
> > +   }
>
> These writes might not be visible to the page table walkers immediately, and
> the TLBs might still contain stale values for a while afterwards.
> That could render the cache maintenance useless (as speculative fetches
> could still occur due to cacheable attributes still being in place).
>
> You need a DSB to ensure writes are visible to the page table walkers (with a
> compiler barrier to ensure that the writes actually occur before the DSB), and
> some TLB maintenance (complete with another DSB) to ensure that the TLBs
> don't contain stale values by the time to get to the cache afterwards.
The flush_dcache _range() below contains a dsb. Isn't it fine enough? Or we need a separte dsb in the for loopafter we changed the cache attribute.
Regarding the TLB maintenance if we have _asm_invalidate_tlb_all() after the flush dcache range below it should be fine right?

>
> Also minor nit, but s/upto/i/?
>
> > +
> > +   start = start << MMU_SECTION_SHIFT;
> > +   end = end << MMU_SECTION_SHIFT;
> > +   flush_dcache_range(start, end);
> > +}
> >  #else      /* CONFIG_SYS_DCACHE_OFF */
> >
> >  void invalidate_dcache_all(void)
> > @@ -170,6 +197,11 @@ int dcache_status(void)
> >     return 0;
> >  }
> >
> > +void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
> > +                                enum dcache_option option)
> > +{
> > +}
> > +
> >  #endif     /* CONFIG_SYS_DCACHE_OFF */
> >
> >  #ifndef CONFIG_SYS_ICACHE_OFF
> > diff --git a/arch/arm/include/asm/system.h
> > b/arch/arm/include/asm/system.h index 760e8ab..868ea54 100644
> > --- a/arch/arm/include/asm/system.h
> > +++ b/arch/arm/include/asm/system.h
> > @@ -15,9 +15,15 @@
> >  #define CR_EE              (1 << 25)       /* Exception (Big) Endian
>       */
> >
> >  #define PGTABLE_SIZE       (0x10000)
> > +/* 2MB granularity */
> > +#define MMU_SECTION_SHIFT  21
>
> Do we only expect 4K pages for now?
Ahh yes for now and can modify it

Regards,
Siva

>
> Thanks,
> Mark.


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[U-Boot] [PATCH v3] armv8: caches: Added routine to set non cacheable region

[Mark Rutland]

On Thu, Jun 11, 2015 at 08:17:15AM +0100, Siva Durga Prasad Paladugu wrote:
> 
> Hi Mark,
> 
> > -----Original Message-----
> > From: Mark Rutland [mailto:mark.rutland at arm.com]
> > Sent: Thursday, May 28, 2015 3:10 PM
> > To: Siva Durga Prasad Paladugu
> > Cc: u-boot at lists.denx.de; Michal Simek; Siva Durga Prasad Paladugu
> > Subject: Re: [PATCH v3] armv8: caches: Added routine to set non cacheable
> > region
> >
> > Hi,
> >
> > > +void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
> > > +                                enum dcache_option option)
> > > +{
> > > +   u64 *page_table = arch_get_page_table();
> > > +   u64 upto, end;
> > > +
> > > +   if (page_table == NULL)
> > > +           return;
> > > +
> > > +   end = ALIGN(start + size, (1 << MMU_SECTION_SHIFT)) >>
> > > +         MMU_SECTION_SHIFT;
> > > +   start = start >> MMU_SECTION_SHIFT;
> > > +   for (upto = start; upto < end; upto++) {
> > > +           page_table[upto] &= ~PMD_ATTRINDX_MASK;
> > > +           page_table[upto] |= PMD_ATTRINDX(option);
> > > +   }
> >
> > These writes might not be visible to the page table walkers immediately, and
> > the TLBs might still contain stale values for a while afterwards.
> > That could render the cache maintenance useless (as speculative fetches
> > could still occur due to cacheable attributes still being in place).
> >
> > You need a DSB to ensure writes are visible to the page table walkers (with a
> > compiler barrier to ensure that the writes actually occur before the DSB), and
> > some TLB maintenance (complete with another DSB) to ensure that the TLBs
> > don't contain stale values by the time to get to the cache afterwards.
> The flush_dcache _range() below contains a dsb. Isn't it fine enough?
> Or we need a separte dsb in the for loopafter we changed the cache
> attribute.

The DSB in flush_dcache_range() is not sufficient. You need a DSB
between the page table modifications and the TLB invalidation, and the
TLB invalidation must be completed before the cache maintenance begins.

> Regarding the TLB maintenance if we have _asm_invalidate_tlb_all()
> after the flush dcache range below it should be fine right?

No. The TLB maintenance must be complete _before_ the cache maintenance,
or the cache can be refilled while the maintenance is ongoing (e.g. the
CPU could make speculative prefetches).

You need a strictly-ordered sequence:

1) Modify the page tables

2) DSB

   This ensures the updates are visible to the page table walker(s).

3) TLB invalidation

4) DSB

   This ensures that the TLB invalidation is complete (i.e. from this
   point on the TLBs cannot hold entries for the region with cacheable
   attributes).

5) ISB

   This ensures that the effects of TLB invalidation are visible to
   later instructions. Otherwise instructions later could be using stale
   attributes fetched earlier by the CPU from the TLB, before the TLB
   invalidation completed (and hence could allocate in the caches).

6) Cache maintenance 

7) DSB to complete cache maintenance

Thanks,
Mark.