145 lines
4.6 KiB
PHP
145 lines
4.6 KiB
PHP
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; Memory management for USB structures.
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; Protocol layer uses the common kernel heap malloc/free.
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; Hardware layer has special requirements:
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; * memory blocks should be properly aligned
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; * memory blocks should not cross page boundary
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; Hardware layer allocates fixed-size blocks.
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; Thus, the specific allocator is quite easy to write:
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; allocate one page, split into blocks, maintain the single-linked
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; list of all free blocks in each page.
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; Note: size must be a multiple of required alignment.
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; Data for one pool: dd pointer to the first page, MUTEX lock.
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; Allocator for fixed-size blocks: allocate a block.
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; [ebx-4] = pointer to the first page, ebx = pointer to MUTEX structure.
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proc usb_allocate_common
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push edi ; save used register to be stdcall
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virtual at esp
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dd ? ; saved edi
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dd ? ; return address
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.size dd ?
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end virtual
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; 1. Take the lock.
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mov ecx, ebx
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call mutex_lock
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; 2. Find the first allocated page with a free block, if any.
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; 2a. Initialize for the loop.
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mov edx, ebx
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.pageloop:
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; 2b. Get the next page, keeping the current in eax.
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mov eax, edx
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mov edx, [edx-4]
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; 2c. If there is no next page, we're out of luck; go to 4.
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test edx, edx
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jz .newpage
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add edx, 0x1000
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@@:
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; 2d. Get the pointer to the first free block on this page.
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; If there is no free block, continue to 2b.
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mov eax, [edx-8]
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test eax, eax
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jz .pageloop
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; 2e. Get the pointer to the next free block.
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mov ecx, [eax]
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; 2f. Update the pointer to the first free block from eax to ecx.
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; Normally [edx-8] still contains eax, if so, atomically set it to ecx
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; and proceed to 3.
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; However, the price of simplicity of usb_free_common (in particular, it
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; doesn't take the lock) is that [edx-8] could (rarely) be changed while
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; we processed steps 2d+2e. If so, return to 2d and retry.
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lock cmpxchg [edx-8], ecx
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jnz @b
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.return:
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; 3. Release the lock taken in step 1 and return.
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push eax
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mov ecx, ebx
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call mutex_unlock
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pop eax
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pop edi ; restore used register to be stdcall
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ret 4
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.newpage:
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; 4. Allocate a new page.
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push eax
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stdcall kernel_alloc, 0x1000
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pop edx
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; If failed, say something to the debug board and return zero.
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test eax, eax
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jz .nomemory
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; 5. Add the new page to the tail of list of allocated pages.
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mov [edx-4], eax
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; 6. Initialize two service dwords in the end of page:
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; first free block is (start of page) + (block size)
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; (we will return first block at (start of page), so consider it allocated),
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; no next page.
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mov edx, eax
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lea edi, [eax+0x1000-8]
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add edx, [.size]
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mov [edi], edx
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and dword [edi+4], 0
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; 7. All blocks starting from edx are free; join them in a single-linked list.
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@@:
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mov ecx, edx
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add edx, [.size]
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mov [ecx], edx
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cmp edx, edi
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jbe @b
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sub ecx, [.size]
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and dword [ecx], 0
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; 8. Return (start of page).
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jmp .return
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.nomemory:
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dbgstr 'no memory for USB descriptor'
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xor eax, eax
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jmp .return
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endp
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; Allocator for fixed-size blocks: free a block.
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proc usb_free_common
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push ecx edx
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virtual at esp
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rd 2 ; saved registers
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dd ? ; return address
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.block dd ?
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end virtual
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; Insert the given block to the head of free blocks in this page.
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mov ecx, [.block]
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mov edx, ecx
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or edx, 0xFFF
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@@:
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mov eax, [edx+1-8]
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mov [ecx], eax
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lock cmpxchg [edx+1-8], ecx
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jnz @b
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pop edx ecx
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ret 4
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endp
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; Helper procedure: translate physical address in ecx
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; of some transfer descriptor to linear address.
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; in: eax = address of first page
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proc usb_td_to_virt
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; Traverse all pages used for transfer descriptors, looking for the one
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; with physical address as in ecx.
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@@:
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test eax, eax
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jz .zero
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push eax
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call get_pg_addr
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sub eax, ecx
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jz .found
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cmp eax, -0x1000
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ja .found
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pop eax
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mov eax, [eax+0x1000-4]
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jmp @b
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.found:
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; When found, combine page address from eax with page offset from ecx.
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pop eax
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and ecx, 0xFFF
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add eax, ecx
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.zero:
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ret
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endp
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