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        ARM-Linux驅動--MTD驅動分析(一)
        
						
        
				作者：
				時間：2016-11-20
				來源：網絡

							
				
				
				
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			主機：Gentoo Linux 11.2 with linux kernel 3.0.6
        硬件平臺：FL2440（S3C2440）with linux kernel 2.6.35
        本文引用地址：http://www.104case.com/article/201611/319012.htm
        MTD(memory technology device內存技術設備) 在硬件和文件系統層之間的提供了一個抽象的接口，MTD是用來訪問內存設備（如：ROM、flash）的中間層，它將內存設備的共有特性抽取出來，從而使增加新的內存設備驅動程序變得更簡單。MTD的源代碼都在/drivers/mtd目錄中。
        MTD中間層細分為四層，按從上到下依次為：設備節點、MTD設備層、MTD原始設備層和硬件驅動層。MTD中間層層次結構圖如下：
        從上圖可以看出，原始設備是MTD字符設備和MTD塊設備的抽象。
        MTD設備層、MTD原始設備層和Flash硬件驅動層之間的接口關系如下圖：
        下面首先分析下MTD原始層設備
        1、mtd_info數據結構
        1. structmtd_info{
        2. u_chartype;//內存技術類型，例如MTD_RAM,MTD_ROM,MTD_NORFLASH,MTD_NAND_FLASH,MTD_PEROM等
        3. uint32_tflags;//標志位
        4. uint64_tsize;//TotalsizeoftheMTD//MTD設備的大小
        6. /*"Major"erasesizeforthedevice.Naïveusersmaytakethis
        7. *tobetheonlyerasesizeavailable,ormayusethemoredetailed
        8. *informationbelowiftheydesire
        9. */
        10. uint32_terasesize;//最小的擦除塊大小
        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;//編程塊大小
        20. uint32_toobsize;//AmountofOOBdataperblock(e.g.16)//oob(Outofband)塊大小
        21. uint32_toobavail;//AvailableOOBbytesperblock//每塊的可用的oob字節
        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布局結構
        40. /*Dataforvariableeraseregions.Ifnumeraseregionsiszero,
        41. *itmeansthatthewholedevicehaserasesizeasgivenabove.
        42. */
        43. intnumeraseregions;//擦除區域個數，通常為1
        44. structmtd_erase_region_info*eraseregions;//擦除區域的區域信息地址
        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);//函數指針，erase函數的功能是將一個erase_info加入擦除隊列
        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函數功能是允許片內執行（XIP）
        60. /*WeprobablyshouldntallowXIPiftheunpointisntaNULL*/
        61. void(*unpoint)(structmtd_info*mtd,loff_tfrom,size_tlen);//unpoint函數與point函數相反，是禁止片內執行（XIP）
        63. /*AllowNOMMUmmap()todirectlymapthedevice(ifnotNULL)
        64. *-returntheaddresstowhichtheoffsetmaps
        65. *-return-ENOSYStoindicaterefusaltodothemapping
        66. */
        67. //如果不是NULL，則允許無MMU單元的地址映射，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設備的讀寫函數
        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,thisfunctioncanbreaklocksanddelaytoensurethewrite
        87. succeeds(butnotsleep).*/
        89. int(*panic_write)(structmtd_info*mtd,loff_tto,size_tlen,size_t*retlen,constu_char*buf);
        91. //用于MTD設備的OBB數據讀寫
        92. int(*read_oob)(structmtd_info*mtd,loff_tfrom,
        93. structmtd_oob_ops*ops);
        94. int(*write_oob)(structmtd_info*mtd,loff_tto,
        95. structmtd_oob_ops*ops);
        97. /*
        98. *Methodstoaccesstheprotectionregisterarea,presentinsome
        99. *flashdevices.Theuserdataisonetimeprogrammablebutthe
        100. *factorydataisreadonly.
        101. */
        102. int(*get_fact_prot_info)(structmtd_info*mtd,structotp_info*buf,size_tlen);
        103. int(*read_fact_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
        104. int(*get_user_prot_info)(structmtd_info*mtd,structotp_info*buf,size_tlen);
        105. int(*read_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
        106. int(*write_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
        107. int(*lock_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen);
        109. /*kvec-basedread/writemethods.
        110. NB:Thecountparameteristhenumberof_vectors_,eachof
        111. whichcontainsan(ofs,len)tuple.
        112. */
        113. int(*writev)(structmtd_info*mtd,conststructkvec*vecs,unsignedlongcount,loff_tto,size_t*retlen);
        115. /*Sync*/
        116. //MTD設備的同步函數
        117. void(*sync)(structmtd_info*mtd);
        119. /*Chip-supporteddevicelocking*/
        120. //芯片的加鎖和解鎖
        121. int(*lock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
        122. int(*unlock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
        124. /*PowerManagementfunctions*/
        125. //支持電源管理函數
        126. int(*suspend)(structmtd_info*mtd);
        127. void(*resume)(structmtd_info*mtd);
        129. /*Badblockmanagementfunctions*/
        130. //壞塊管理函數
        131. int(*block_isbad)(structmtd_info*mtd,loff_tofs);
        132. int(*block_markbad)(structmtd_info*mtd,loff_tofs);
        134. structnotifier_blockreboot_notifier;/*defaultmodebeforereboot*/
        136. /*ECCstatusinformation*/
        137. structmtd_ecc_statsecc_stats;//ECC狀態信息
        138. /*Subpageshift(NAND)*/
        139. intsubpage_sft;
        141. void*priv;//私有數據指針
        143. structmodule*owner;
        144. structdevicedev;
        145. intusecount;//記錄用戶的個數
        147. /*Ifthedriverissomethingsmart,likeUBI,itmayneedtomaintain
        148. *itsownreferencecounting.Thebelowfunctionsareonlyfordriver.
        149. *Thedrivermayregisteritscallbacks.Thesecallbacksarenot
        150. *supposedtobecalledbyMTDusers*/
        151. //驅動回調函數
        152. int(*get_device)(structmtd_info*mtd);
        153. void(*put_device)(structmtd_info*mtd);
        154. };

        2、mtd_part結構體信息
        1. /*Ourpartitionlinkedlist*/
        2. staticLIST_HEAD(mtd_partitions);//分區鏈表
        1. /*Ourpartitionnodestructure*/
        2. //分區結構信息
        3. structmtd_part{
        4. structmtd_infomtd;//mtd_info數據結構，會被加入mtd_table中
        5. structmtd_info*master;//該分區的主分區
        6. uint64_toffset;//該分區的偏移地址
        7. structlist_headlist;//分區鏈表
        8. };

        3、mtd_partition描述mtd具體分區結構
        1. /*
        2. *Partitiondefinitionstructure:
        3. *
        4. *AnarrayofstructpartitionispassedalongwithaMTDobjectto
        5. *add_mtd_partitions()tocreatethem.
        6. *
        7. *Foreachpartition,thesefieldsareavailable:
        8. *name:stringthatwillbeusedtolabelthepartitionsMTDdevice.
        9. *size:thepartitionsize;ifdefinedasMTDPART_SIZ_FULL,thepartition
        10. *willextendtotheendofthemasterMTDdevice.
        11. *offset:absolutestartingpositionwithinthemasterMTDdevice;if
        12. *definedasMTDPART_OFS_APPEND,thepartitionwillstartwherethe
        13. *previousoneended;ifMTDPART_OFS_NXTBLK,atthenexteraseblock.
        14. *mask_flags:containsflagsthathavetobemasked(removed)fromthe
        15. *masterMTDflagsetforthecorrespondingMTDpartition.
        16. *Forexample,toforcearead-onlypartition,simplyadding
        17. *MTD_WRITEABLEtothemask_flagswilldothetrick.
        18. *
        19. *Note:writeablepartitionsrequiretheirsizeandoffsetbe
        20. *erasesizealigned(e.g.useMTDPART_OFS_NEXTBLK).
        21. */
        23. structmtd_partition{
        24. char*name;/*identifierstring分區名*/
        25. uint64_tsize;/*partitionsize分區大小*/
        26. uint64_toffset;/*offsetwithinthemasterMTDspace偏移地址*/
        27. uint32_tmask_flags;/*masterMTDflagstomaskoutforthispartition*/
        28. structnand_ecclayout*ecclayout;/*outofbandlayoutforthispartition(NANDonly)*/
        29. }; 

        
				
            
                
			
							
        
                
			              
              
            
        
		
        
		
        
		
        
		
        
		
        
			
          
				
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