[U-Boot] [Patch v4 2/5] ARMv8: Adjust MMU setup

York Sun
2014-06-04T16:27:30Z

On 06/02/2014 11:01 AM, Mark Rutland wrote:
> On Mon, Jun 02, 2014 at 05:06:13PM +0100, York Sun wrote:
>> On 06/02/2014 04:34 AM, Mark Rutland wrote:
>>> On Thu, May 29, 2014 at 09:49:05PM +0100, York Sun wrote:
>>>> Make MMU functions reusable. Platform code can setup its own MMU tables.
>>>
>>> What exactly does platform code need to setup its own tables for?
>>
>> The general ARMv8 MMU table is not detail enough to control memory attribute
>> like cache for all addresses. We have devices mapping to addresses with
>> different requirement for cache control.
>
> And there are no APIs for creating device mappings rather than exporting
> the raw pagetable accessors and hard-coding them differently in every
> board file?
>

That's a good question. At this point, only two platforms are using ARMv8 code.
I am expecting FSL ARMv8 implementation will stay similar, i.e. covered by the
file I added. If that's not the case, or more ARMv8 SoCs need special MMU table,
we then should introduce such API. Having a full function MMU API may be an
overkill for U-boot. We don't need dynamic MMU anyway.

>>
>>>
>>>> Also fix a typo of "TCR_EL3_IPS_BITS" in cache_v8.c.
>>>>
>>>> Signed-off-by: York Sun <yorksun@freescale.com>
>>>> CC: David Feng <fenghua@phytium.com.cn>
>>>> ---
>>>> Change log:
>>>> v4: new patch, splitted from v3 2/4
>>>> Revise set_pgtable_section() to be reused by platform MMU code
>>>> Add inline function set_ttbr_tcr_mair() to be used by this and platform mmu code
>>>>
>>>> arch/arm/cpu/armv8/cache_v8.c | 49 ++++++++++++++++----------------------
>>>> arch/arm/include/asm/armv8/mmu.h | 23 ++++++++++++++++++
>>>> 2 files changed, 43 insertions(+), 29 deletions(-)
>>>>
>>>> diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
>>>> index a96ecda..67dbd46 100644
>>>> --- a/arch/arm/cpu/armv8/cache_v8.c
>>>> +++ b/arch/arm/cpu/armv8/cache_v8.c
>>>> @@ -12,15 +12,14 @@
>>>> DECLARE_GLOBAL_DATA_PTR;
>>>>
>>>> #ifndef CONFIG_SYS_DCACHE_OFF
>>>> -
>>>> -static void set_pgtable_section(u64 section, u64 memory_type)
>>>> +void set_pgtable_section(u64 *page_table, u64 index, u64 section,
>>>> + u64 memory_type)
>>>> {
>>>> - u64 *page_table = (u64 *)gd->arch.tlb_addr;
>>>> u64 value;
>>>>
>>>> - value = (section << SECTION_SHIFT) | PMD_TYPE_SECT | PMD_SECT_AF;
>>>> + value = section | PMD_TYPE_SECT | PMD_SECT_AF;
>>>> value |= PMD_ATTRINDX(memory_type);
>>>> - page_table[section] = value;
>>>> + page_table[index] = value;
>>>> }
>>>>
>>>> /* to activate the MMU we need to set up virtual memory */
>>>> @@ -28,10 +27,13 @@ static void mmu_setup(void)
>>>> {
>>>> int i, j, el;
>>>> bd_t *bd = gd->bd;
>>>> + u64 *page_table = (u64 *)gd->arch.tlb_addr;
>>>>
>>>> /* Setup an identity-mapping for all spaces */
>>>> - for (i = 0; i < (PGTABLE_SIZE >> 3); i++)
>>>> - set_pgtable_section(i, MT_DEVICE_NGNRNE);
>>>> + for (i = 0; i < (PGTABLE_SIZE >> 3); i++) {
>>>> + set_pgtable_section(page_table, i, i << SECTION_SHIFT,
>>>> + MT_DEVICE_NGNRNE);
>>>> + }
>>>>
>>>> /* Setup an identity-mapping for all RAM space */
>>>> for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
>>>> @@ -39,36 +41,25 @@ static void mmu_setup(void)
>>>> ulong end = bd->bi_dram[i].start + bd->bi_dram[i].size;
>>>> for (j = start >> SECTION_SHIFT;
>>>> j < end >> SECTION_SHIFT; j++) {
>>>> - set_pgtable_section(j, MT_NORMAL);
>>>> + set_pgtable_section(page_table, j, j << SECTION_SHIFT,
>>>> + MT_NORMAL);
>>>> }
>>>> }
>>>>
>>>> /* load TTBR0 */
>>>> el = current_el();
>>>> if (el == 1) {
>>>> - asm volatile("msr ttbr0_el1, %0"
>>>> - : : "r" (gd->arch.tlb_addr) : "memory");
>>>> - asm volatile("msr tcr_el1, %0"
>>>> - : : "r" (TCR_FLAGS | TCR_EL1_IPS_BITS)
>>>> - : "memory");
>>>> - asm volatile("msr mair_el1, %0"
>>>> - : : "r" (MEMORY_ATTRIBUTES) : "memory");
>>>> + set_ttbr_tcr_mair(el, gd->arch.tlb_addr,
>>>> + TCR_FLAGS | TCR_EL1_IPS_BITS,
>>>> + MEMORY_ATTRIBUTES);
>>>> } else if (el == 2) {
>>>> - asm volatile("msr ttbr0_el2, %0"
>>>> - : : "r" (gd->arch.tlb_addr) : "memory");
>>>> - asm volatile("msr tcr_el2, %0"
>>>> - : : "r" (TCR_FLAGS | TCR_EL2_IPS_BITS)
>>>> - : "memory");
>>>> - asm volatile("msr mair_el2, %0"
>>>> - : : "r" (MEMORY_ATTRIBUTES) : "memory");
>>>> + set_ttbr_tcr_mair(el, gd->arch.tlb_addr,
>>>> + TCR_FLAGS | TCR_EL2_IPS_BITS,
>>>> + MEMORY_ATTRIBUTES);
>>>> } else {
>>>> - asm volatile("msr ttbr0_el3, %0"
>>>> - : : "r" (gd->arch.tlb_addr) : "memory");
>>>> - asm volatile("msr tcr_el3, %0"
>>>> - : : "r" (TCR_FLAGS | TCR_EL2_IPS_BITS)
>>>> - : "memory");
>>>> - asm volatile("msr mair_el3, %0"
>>>> - : : "r" (MEMORY_ATTRIBUTES) : "memory");
>>>> + set_ttbr_tcr_mair(el, gd->arch.tlb_addr,
>>>> + TCR_FLAGS | TCR_EL3_IPS_BITS,
>>>> + MEMORY_ATTRIBUTES);
>>>> }
>>>>
>>>> /* enable the mmu */
>>>> diff --git a/arch/arm/include/asm/armv8/mmu.h b/arch/arm/include/asm/armv8/mmu.h
>>>> index 1193e76..7de4ff9 100644
>>>> --- a/arch/arm/include/asm/armv8/mmu.h
>>>> +++ b/arch/arm/include/asm/armv8/mmu.h
>>>> @@ -108,4 +108,27 @@
>>>> TCR_IRGN_WBWA | \
>>>> TCR_T0SZ(VA_BITS))
>>>>
>>>> +#ifndef __ASSEMBLY__
>>>> +void set_pgtable_section(u64 *page_table, u64 index,
>>>> + u64 section, u64 memory_type);
>>>> +static inline void set_ttbr_tcr_mair(int el, u64 table, u64 tcr, u64 attr)
>>>> +{
>>>> + asm volatile("dsb sy;isb");
>>>
>>> Huh? This wasn't anywhere before. Is the isb necessary?
>>
>> Probably not, but to make sure all previous instructions finish.
>
> Which instructions do you care about completing?
>
> You'll certainly want any page table writes to complete, but is anything
> else in-flight at this point in time?

Before calling this inline function, MMU tables were created. We want the
writing completes before setting these registers.

>
>>>
>>> When is this function expected to be called? Is the MMU expected to be
>>> on?
>>
>> The general ARMv8 code calls this when MMU is off. For the SoC I am enabling, it
>> is called when MMU is off for the first time, but MMU on for the 2nd time.
>
> Ok.
>
>>
>>>
>>>> + if (el == 1) {
>>>> + asm volatile("msr ttbr0_el1, %0" : : "r" (table) : "memory");
>>>> + asm volatile("msr tcr_el1, %0" : : "r" (tcr) : "memory");
>>>> + asm volatile("msr mair_el1, %0" : : "r" (attr) : "memory");
>>>
>>> If the MMU is on, this looks really scary -- what are you expecting to
>>> change in a single invocation?
>>
>> It is not scary for general ARMv8 code. MMU is off then this is called. For FSL
>> SoC, I have these called for the 2nd time, when MMU is on. The 2nd time call
>> points to a new MMU table.
>
> Oh but it is ;)
>
>>
>>>
>>>> + } else if (el == 2) {
>>>> + asm volatile("msr ttbr0_el2, %0" : : "r" (table) : "memory");
>>>> + asm volatile("msr tcr_el2, %0" : : "r" (tcr) : "memory");
>>>> + asm volatile("msr mair_el2, %0" : : "r" (attr) : "memory");
>>>> + } else if (el == 3) {
>>>> + asm volatile("msr ttbr0_el3, %0" : : "r" (table) : "memory");
>>>> + asm volatile("msr tcr_el3, %0" : : "r" (tcr) : "memory");
>>>> + asm volatile("msr mair_el3, %0" : : "r" (attr) : "memory");
>>>> + } else {
>>>> + hang();
>>>> + }
>>>
>>> And no synchronisation to ensure that these writes are complete or even
>>> ordered w.r.t. each other?
>>>
>>
>> That's why I added asm volatile("dsb sy;isb") before them. The order of these
>> write doesn't matter. See the code before my change
>> http://git.denx.de/?p=u-boot.git;a=blob;f=arch/arm/cpu/armv8/cache_v8.c;h=a96ecda7e3146996d20a2e46b975dced2769255c;hb=HEAD
>
> Ok, so that orders them against everything _before_ them, but not with
> respect to each other, or anything _after_ them.
>
> When the MMU is off, you are correct that the ordering of these
> operations w.r.t. each other doesn't matter. With the MMU on that's not
> true as the CPU can rerder the operations and can walk the page tables
> asynchronously.
>
> Changing the MAIR at runtime is somewhat scary because you may be
> changing attributes for entries which are active in the cache and/or
> TLBs. I'm not sure I follow why you need to change it once the MMU is on
> -- there are plenty of subfields in the MAIR that you could configure
> before turning the MMU on for use later.
>
> Likewise changing the TCR at runtime is somewhat scary because you can
> change attributes of active cache and/or TLB entries, change fields that
> affect the way page tables are walked (TG*. T*SZ), all asynchronously
> w.r.t. the logic that walsk the page tables.
>
> Changing the TTBR is fine, except that we didn't invalidate old entries
> with a TLBI, so we may even have partial translations cahced in the
> TLBs, and we can get odd translations generated from the combination of
> the old and new tables.

Maybe a more proper way to do so is to change TTBR only. That's actually what I
really need. Or if I really need to change all of them, I should turn off MMU first.

>
>> For the 2nd write used by FSL SoC, I need to flush the cache to make sure the
>> table is in main DDR and perform TLB invalidation. That's when the loading of
>> new MMU table happens.
>
> I missed the TLB invaliation -- where is that meant to happen?
>
After flushing the new MMU table into DDR. To your point above, I will send a
new version with updating TTBR only.

York