The call to create_flat_mapping() in mmu.c will change both memory
type and shareability of all RAM in use by barebox while MMU is on
when done in conjunction with CONFIG_MMU_EARLY. According to "ARM
Reference Manual. ARMv7-A and ARMv7-R edition", this warrants the use
of "break-before-make" algorithm for TTB entries replacement,
nontheless original code seemed to work well without any hint of a
problem in the case of running from DRAM.
Running it on VF610, when executing from SRAM (uploaded via JTAG),
however proved to be problematic, with the following patch:
-------------------- 8< -------------------------------------------
diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
index aa1a7c09c..650e20828 100644
--- a/arch/arm/cpu/mmu.c
+++ b/arch/arm/cpu/mmu.c
@@ -419,6 +419,11 @@ static void vectors_init(void)
create_vector_table(ARM_LOW_VECTORS);
}
+static void dump_bank(struct memory_bank *b)
+{
+ pr_crit("0x%08lx - 0x%08lx\n", b->start, b->start + b->size - 1);
+}
+
/*
* Prepare MMU for usage enable it.
*/
@@ -494,6 +499,7 @@ static int mmu_init(void)
* below
*/
for_each_memory_bank(bank) {
+ dump_bank(bank);
create_sections(ttb, bank->start, bank->size,
PMD_SECT_DEF_CACHED);
__mmu_cache_flush();
@@ -501,6 +507,10 @@ static int mmu_init(void)
__mmu_cache_on();
+ pr_info("%s %d\n", __func__, __LINE__);
+ for_each_memory_bank(bank)
+ dump_bank(bank);
+
return 0;
}
mmu_initcall(mmu_init);
-------------------- >8 -------------------------------------------
when applied, produces the following output on Zii VF610 Dev board:
-------------------- 8< -------------------------------------------
barebox 2018.04.0-00195-ge7ba82254-dirty #552 Thu Apr 19 11:32:56 PDT 2018
Board: VF610 OCRAM
i.MX clk 9: register failed with -22
i.MX clk 10: register failed with -22
i.MX clk 160: register failed with -22
mmu: Critical Error: Can't request SDRAM region for ttb at 3f078000
mmu: 0x80000000 - 0x9fffffff
mmu: 0x80000000 - 0x9fffffff
mmu: mmu_init 510
unable to handle NULL pointer dereference at address 0x00000000
pc : [<3f01b7da>] lr : [<3f01b7d1>]
sp : 3f07ff38 ip : 00000000 fp : 00000000
r10: 00000000 r9 : 3f000009 r8 : 00000c0e
r7 : 3f0258aa r6 : 3f0258aa r5 : 3f413b80 r4 : 00000000
r3 : 3f02f1b4 r2 : b0000000 r1 : 0000000a r0 : 00000012
Flags: nZCv IRQs off FIQs off Mode SVC_32
[<3f01b7da>] (mmu_init+0xce/0x168) from [<3f000b9d>] (start_barebox+0x45/0x98)
[<3f000b9d>] (start_barebox+0x45/0x98) from [<3f01bb19>] (barebox_non_pbl_start+0x95/0xd4)
[<3f01bb19>] (barebox_non_pbl_start+0x95/0xd4) from [<3f01bb71>] (barebox_arm_entry+0x19/0x1c)
[<3f01d085>] (unwind_backtrace+0x1/0x58) from [<3f000e45>] (panic+0x1d/0x2c)
[<3f000e45>] (panic+0x1d/0x2c) from [<3f01b5d1>] (do_exception+0xd/0x10)
[<3f01b5d1>] (do_exception+0xd/0x10) from [<3f01b631>] (do_data_abort+0x21/0x2c)
[<3f01b631>] (do_data_abort+0x21/0x2c) from [<3f01b3d4>] (do_abort_6+0x48/0x54)
\### ERROR ### Please RESET the board ###
-------------------- 8< -------------------------------------------
every boot. Compared to regular output (no-MMU build):
barebox 2018.04.0-00195-ge7ba82254-dirty #553 Thu Apr 19 12:03:17 PDT 2018
Board: VF610 OCRAM
i.MX clk 9: register failed with -22
i.MX clk 10: register failed with -22
i.MX clk 160: register failed with -22
mmu: 0x80000000 - 0x9fffffff
mmu: mmu_init 493
mmu: 0x80000000 - 0x9fffffff
Error: Cannot request SDRAM region for stack
Warning: Using dummy clocksource
malloc space: 0x3f400000 -> 0x3f47ffff (size 512 KiB)
environment load /dev/env0: No such file or directory
Maybe you have to create the partition.
running /env/bin/init...
Hit any key to stop autoboot: 3
barebox@VF610 OCRAM:/
-------------------- >8 -------------------------------------------
Note that, in the first listing, buggy execution starts from "mmu:
0x80000000 - 0x9fffffff mmu: 0x80000000 - 0x9fffffff" is printed
twice. Compiling with CONFIG_MMU_EARLY=n make the issue go
aways. The following patch:
-------------------- 8< -------------------------------------------
@@ -479,6 +479,7 @@ static int mmu_init(void)
create_flat_mapping(ttb);
__mmu_cache_flush();
+ tlb_invalidate();
vectors_init();
-------------------- >8 -------------------------------------------
seem to fix the issue as well. This patch however, opts to implement a
third solution and converts the code to disable MMU as a first step,
because it seems to be a safer approach and it also allows us to drop
a lot of extra code needed for error handling.
Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
---
Sascha:
The precise mechanics of this failure are not 100% clear to me and
both solutions to this problem were discovered through trial and
error.
I am more than happy to run more experiments to diagnose this issue if
anyone has any suggestinons.
Feedback is wellcome!
Thanks,
Andrey Smirnov
arch/arm/cpu/mmu.c | 27 +++++----------------------
1 file changed, 5 insertions(+), 22 deletions(-)
diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
index a89f420f2..bb25f6b4f 100644
--- a/arch/arm/cpu/mmu.c
+++ b/arch/arm/cpu/mmu.c
@@ -450,36 +450,20 @@ static int mmu_init(void)
if (get_cr() & CR_M) {
/*
- * Early MMU code has already enabled the MMU. We assume a
- * flat 1:1 section mapping in this case.
+ * Early MMU code has already enabled the MMU. To
+ * start form a clean slate we need to disable it
+ * first.
*/
- asm volatile ("mrc p15,0,%0,c2,c0,0" : "=r"(ttb));
-
- /* Clear unpredictable bits [13:0] */
- ttb = (uint32_t *)((unsigned long)ttb & ~0x3fff);
-
- if (!request_sdram_region("ttb", (unsigned long)ttb, SZ_16K))
- /*
- * This can mean that:
- * - the early MMU code has put the ttb into a place
- * which we don't have inside our available memory
- * - Somebody else has occupied the ttb region which means
- * the ttb will get corrupted.
- */
- pr_crit("Critical Error: Can't request SDRAM region for ttb at %p\n",
- ttb);
- } else {
- ttb = xmemalign(ARM_TTB_SIZE, ARM_TTB_SIZE);
+ mmu_disable();
}
+ ttb = xmemalign(ARM_TTB_SIZE, ARM_TTB_SIZE);
pr_debug("ttb: 0x%p\n", ttb);
set_ttbr(ttb);
set_domain(DOMAIN_MANAGER);
create_flat_mapping(ttb);
- __mmu_cache_flush();
-
vectors_init();
/*
@@ -490,7 +474,6 @@ static int mmu_init(void)
for_each_memory_bank(bank) {
create_sections(ttb, bank->start, bank->start + bank->size - 1,
PMD_SECT_DEF_CACHED);
- __mmu_cache_flush();
}
__mmu_cache_on();
--
2.17.0
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