6/25/2011 10:56:51 PM

6/25/2011 10:56:51 PM

HZ 表示1s时钟中断的次数
tick 表示一次时钟中断的时间

pxafb_disable_controller 最后还关闭了LCD的时钟

看看是如果启动的

if (old_state != C_ENABLE) {
fbi->state = C_ENABLE;
pxafb_setup_gpio(fbi);
pxafb_enable_controller(fbi);
__pxafb_lcd_power(fbi, 1);
#ifdef CONFIG_LITTLETON_SMART_PANEL
wake_up_interruptible(&screen_update_wait_q);
#endif
__pxafb_backlight_power(fbi, 1);
if(fbi->set_overlay_ctrlr_state)
fbi->set_overlay_ctrlr_state(fbi, C_ENABLE);
}

pxafb_setup_gpio

开始映射内存了

pxafb_map_video_memory

fbi->map_size = PAGE_ALIGN(fbi->fb.fix.smem_len + 4 * PAGE_SIZE);

预留了4个page

Write combining (WC)[1] is a computer bus technique for allowing data to be combined and temporarily stored in a buffer -- the write combine buffer (WCB) -- to be released together later in burst mode instead of writing (immediately) as single bits or small chunks.

Write combining cannot be used for general memory access (data or code regions) due to the 'weak ordering'. Write-combining does not guarantee that the combination of writes and reads is done in the correct order. For example, a Write/Read/Write combination to a specific address would lead to the write combining order of Read/Write/Write which can lead to obtaining wrong values with the first read (which potentially relies on the write before).

In order to avoid the problem of read/write order described above, the write buffer can be treated as a fully-associative cache and added into the memory hierarchy of the device in which it is implemented[2]. Adding complexity slows down the memory hierarchy so this technique is often only used for memory which does not need 'strong ordering' (always correct) like the frame buffers of video cards.

struct page {
unsigned long flags; /* Atomic flags, some possibly
* updated asynchronously */
atomic_t _count; /* Usage count, see below. */
atomic_t _mapcount; /* Count of ptes mapped in mms,
* to show when page is mapped
* & limit reverse map searches.
*/
union {
struct {
unsigned long private; /* Mapping-private opaque data:
* usually used for buffer_heads
* if PagePrivate set; used for
* swp_entry_t if PageSwapCache;
* indicates order in the buddy
* system if PG_buddy is set.
*/
struct address_space *mapping; /* If low bit clear, points to
* inode address_space, or NULL.
* If page mapped as anonymous
* memory, low bit is set, and
* it points to anon_vma object:
* see PAGE_MAPPING_ANON below.
*/
};
#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
spinlock_t ptl;
#endif
};
pgoff_t index; /* Our offset within mapping. */
struct list_head lru; /* Pageout list, eg. active_list
* protected by zone->lru_lock !
*/
/*
* On machines where all RAM is mapped into kernel address space,
* we can simply calculate the virtual address. On machines with
* highmem some memory is mapped into kernel virtual memory
* dynamically, so we need a place to store that address.
* Note that this field could be 16 bits on x86 ... ;)
*
* Architectures with slow multiplication can define
* WANT_PAGE_VIRTUAL in asm/page.h
*/
#if defined(WANT_PAGE_VIRTUAL)
void *virtual; /* Kernel virtual address (NULL if
not kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */
};

用来描述一个物理页

struct vm_region {
struct list_head vm_list;
unsigned long vm_start;
unsigned long vm_end;
struct page *vm_pages;
int vm_active;
};

arm 中用来描述一块虚拟地址空间

#define CONSISTENT_DMA_SIZE SZ_8M

定义了8M的DMA区域

#define NUM_CONSISTENT_PTES (CONSISTENT_DMA_SIZE >> PGDIR_SHIFT)

/*
* These are the page tables (2MB each) covering uncached, DMA consistent allocations
*/
static pte_t *consistent_pte[NUM_CONSISTENT_PTES];

每个页表项就是2M

也就是说8M的DMA区域可以分成4个不同的页表项

要分配也是在这4个页表项中进行分配

如果第一个pte就是null，就返回失败

if (!consistent_pte[0]) {
printk(KERN_ERR "%s: not initialised/n", __func__);
dump_stack();
return NULL;
}

u64 *dma_mask; /* dma mask (if dma'able device) */
u64 coherent_dma_mask;/* Like dma_mask, but for
alloc_coherent mappings as
not all hardware supports
64 bit addresses for consistent
allocations such descriptors. */

DMA掩码

一致性DMA掩码

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　　AMBA总线是一个多总线系统。规范定义了三种可以组合使用的不同类型的总线：AHB（Advanced High-performance Bus）、ASB（Advanced System Bus）和APB（Advanced Peripheral Bus）

AMBA 高级微控总线协议