cpu-defs.h: Document CPUIOTLBEntry 'addr' field
The 'addr' field in the CPUIOTLBEntry struct has a rather non-obvious use; add a comment documenting it (reverse-engineered from what the code that sets it is doing). Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20180611125633.32755-2-peter.maydell@linaro.org
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@ -664,6 +664,18 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
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env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
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env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
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/* refill the tlb */
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/* refill the tlb */
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/*
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* At this point iotlb contains a physical section number in the lower
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* TARGET_PAGE_BITS, and either
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* + the ram_addr_t of the page base of the target RAM (if NOTDIRTY or ROM)
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* + the offset within section->mr of the page base (otherwise)
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* We subtract the vaddr (which is page aligned and thus won't
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* disturb the low bits) to give an offset which can be added to the
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* (non-page-aligned) vaddr of the eventual memory access to get
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* the MemoryRegion offset for the access. Note that the vaddr we
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* subtract here is that of the page base, and not the same as the
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* vaddr we add back in io_readx()/io_writex()/get_page_addr_code().
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*/
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env->iotlb[mmu_idx][index].addr = iotlb - vaddr;
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env->iotlb[mmu_idx][index].addr = iotlb - vaddr;
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env->iotlb[mmu_idx][index].attrs = attrs;
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env->iotlb[mmu_idx][index].attrs = attrs;
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@ -127,6 +127,15 @@ QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS));
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* structs into one.)
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* structs into one.)
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*/
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*/
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typedef struct CPUIOTLBEntry {
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typedef struct CPUIOTLBEntry {
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/*
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* @addr contains:
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* - in the lower TARGET_PAGE_BITS, a physical section number
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* - with the lower TARGET_PAGE_BITS masked off, an offset which
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* must be added to the virtual address to obtain:
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* + the ram_addr_t of the target RAM (if the physical section
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* number is PHYS_SECTION_NOTDIRTY or PHYS_SECTION_ROM)
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* + the offset within the target MemoryRegion (otherwise)
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*/
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hwaddr addr;
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hwaddr addr;
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MemTxAttrs attrs;
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MemTxAttrs attrs;
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} CPUIOTLBEntry;
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} CPUIOTLBEntry;
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