ARM-Linux驱动--MTD驱动分析(一)

硬件平台：FL2440（S3C2440）with linux kernel 2.6.35

MTD(memory technology device内存技术设备) 在硬件和文件系统层之间的提供了一个抽象的接口，MTD是用来访问内存设备（如：ROM、flash）的中间层，它将内存设备的共有特性抽取出来，从而使增加新的内存设备驱动程序变得更简单。MTD的源代码都在/drivers/mtd目录中。

MTD中间层细分为四层，按从上到下依次为：设备节点、MTD设备层、MTD原始设备层和硬件驱动层。MTD中间层层次结构图如下：

从上图可以看出，原始设备是MTD字符设备和MTD块设备的抽象。

MTD设备层、MTD原始设备层和Flash硬件驱动层之间的接口关系如下图：

下面首先分析下MTD原始层设备

1、mtd_info数据结构

1. structmtd_info{
2. u_chartype;//内存技术类型，例如MTD_RAM,MTD_ROM,MTD_NORFLASH,MTD_NAND_FLASH,MTD_PEROM等
3. uint32_tflags;//标志位
4. uint64_tsize;//TotalsizeoftheMTD//MTD设备的大小
6. /*"Major"erasesizeforthedevice.Naïveusersmaytakethis
7. *tobetheonlyerasesizeavailable,ormayusethemoredetailed
8. *informationbelowiftheydesire
9. */
10. uint32_terasesize;//最小的擦除块大小
11. /*Minimalwritableflashunitsize.IncaseofNORflashitis1(even
12. *thoughindividualbitscanbecleared),incaseofNANDflashitis
13. *oneNANDpage(orhalf,orone-fourthsofit),incaseofECC-edNOR
14. *itisofECCblocksize,etc.Itisillegaltohavewritesize=0.
15. *Anydriverregisteringastructmtd_infomustensureawritesizeof
16. *1orlarger.
17. */
18. uint32_twritesize;//编程块大小
20. uint32_toobsize;//AmountofOOBdataperblock(e.g.16)//oob(Outofband)块大小
21. uint32_toobavail;//AvailableOOBbytesperblock//每块的可用的oob字节
23. /*
24. *Iferasesizeisapowerof2thentheshiftisstoredin
25. *erasesize_shiftotherwiseerasesize_shiftiszero.Dittowritesize.
26. */
27. unsignedinterasesize_shift;
28. unsignedintwritesize_shift;
29. /*Masksbasedonerasesize_shiftandwritesize_shift*/
30. unsignedinterasesize_mask;
31. unsignedintwritesize_mask;
33. //Kernel-onlystuffstartshere.
34. constchar*name;
35. intindex;
37. /*ecclayoutstructurepointer-readonly!*/
38. structnand_ecclayout*ecclayout;//eec布局结构
40. /*Dataforvariableeraseregions.Ifnumeraseregionsiszero,
41. *itmeansthatthewholedevicehaserasesizeasgivenabove.
42. */
43. intnumeraseregions;//擦除区域个数，通常为1
44. structmtd_erase_region_info*eraseregions;//擦除区域的区域信息地址
46. /*
47. *Eraseisanasynchronousoperation.Devicedriversaresupposed
48. *tocallinstr->callback()whenevertheoperationcompletes,even
49. *ifitcompleteswithafailure.
50. *Callersaresupposedtopassacallbackfunctionandwaitforit
51. *tobecalledbeforewritingtotheblock.
52. */
53. int(*erase)(structmtd_info*mtd,structerase_info*instr);//函数指针，erase函数的功能是将一个erase_info加入擦除队列
55. /*ThisstuffforeXecute-In-Place*/
56. /*physisoptionalandmaybesettoNULL*/
57. int(*point)(structmtd_info*mtd,loff_tfrom,size_tlen,
58. size_t*retlen,void**virt,resource_size_t*phys);//point函数功能是允许片内执行（XIP）
60. /*WeprobablyshouldntallowXIPiftheunpointisntaNULL*/
61. void(*unpoint)(structmtd_info*mtd,loff_tfrom,size_tlen);//unpoint函数与point函数相反，是禁止片内执行（XIP）
63. /*AllowNOMMUmmap()todirectlymapthedevice(ifnotNULL)
64. *-returntheaddresstowhichtheoffsetmaps
65. *-return-ENOSYStoindicaterefusaltodothemapping
66. */
67. //如果不是NULL，则允许无MMU单元的地址映射，返回偏移地址
68. unsignedlong(*get_unmapped_area)(structmtd_info*mtd,
69. unsignedlonglen,
70. unsignedlongoffset,
71. unsignedlongflags);
73. /*Backingdevicecapabilitiesforthisdevice
74. *-providesmmapcapabilities
75. */
76. structbacking_dev_info*backing_dev_info;
78. //MTD设备的读写函数
79. int(*read)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
80. int(*write)(structmtd_info*mtd,loff_tto,size_tlen,size_t*retlen,constu_char*buf);
82. /*Inblackboxflightrecorderlikescenarioswewanttomakesuccessful
83. writesininterruptcontext.panic_write()isonlyintendedtobe
84. calledwhenitsknownthekernelisabouttopanicandweneedthe
85. writetosucceed.Sincethekernelisnotgoingtoberunningformuch
86. longer,thisfunctioncanbreaklock