ARM-Linux驅(qū)動(dòng)--MTD驅(qū)動(dòng)分析(一)

作者：時(shí)間：2016-11-20 來(lái)源：網(wǎng)絡(luò)

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主機(jī)：Gentoo Linux 11.2 with linux kernel 3.0.6

硬件平臺(tái)：FL2440（S3C2440）with linux kernel 2.6.35

本文引用地址：http://www.biyoush.com/article/201611/319012.htm

MTD(memory technology device內(nèi)存技術(shù)設(shè)備) 在硬件和文件系統(tǒng)層之間的提供了一個(gè)抽象的接口，MTD是用來(lái)訪問(wèn)內(nèi)存設(shè)備（如：ROM、flash）的中間層，它將內(nèi)存設(shè)備的共有特性抽取出來(lái)，從而使增加新的內(nèi)存設(shè)備驅(qū)動(dòng)程序變得更簡(jiǎn)單。MTD的源代碼都在/drivers/mtd目錄中。

MTD中間層細(xì)分為四層，按從上到下依次為：設(shè)備節(jié)點(diǎn)、MTD設(shè)備層、MTD原始設(shè)備層和硬件驅(qū)動(dòng)層。MTD中間層層次結(jié)構(gòu)圖如下：

從上圖可以看出，原始設(shè)備是MTD字符設(shè)備和MTD塊設(shè)備的抽象。

MTD設(shè)備層、MTD原始設(shè)備層和Flash硬件驅(qū)動(dòng)層之間的接口關(guān)系如下圖：

下面首先分析下MTD原始層設(shè)備

1、mtd_info數(shù)據(jù)結(jié)構(gòu)

structmtd_info{
u_chartype;//內(nèi)存技術(shù)類型，例如MTD_RAM,MTD_ROM,MTD_NORFLASH,MTD_NAND_FLASH,MTD_PEROM等
uint32_tflags;//標(biāo)志位
uint64_tsize;//TotalsizeoftheMTD//MTD設(shè)備的大小
/*"Major"erasesizeforthedevice.Naïveusersmaytakethis
*tobetheonlyerasesizeavailable,ormayusethemoredetailed
*informationbelowiftheydesire
*/
uint32_terasesize;//最小的擦除塊大小
/*Minimalwritableflashunitsize.IncaseofNORflashitis1(even
*thoughindividualbitscanbecleared),incaseofNANDflashitis
*oneNANDpage(orhalf,orone-fourthsofit),incaseofECC-edNOR
*itisofECCblocksize,etc.Itisillegaltohavewritesize=0.
*Anydriverregisteringastructmtd_infomustensureawritesizeof
*1orlarger.
*/
uint32_twritesize;//編程塊大小
uint32_toobsize;//AmountofOOBdataperblock(e.g.16)//oob(Outofband)塊大小
uint32_toobavail;//AvailableOOBbytesperblock//每塊的可用的oob字節(jié)
/*
*Iferasesizeisapowerof2thentheshiftisstoredin
*erasesize_shiftotherwiseerasesize_shiftiszero.Dittowritesize.
*/
unsignedinterasesize_shift;
unsignedintwritesize_shift;
/*Masksbasedonerasesize_shiftandwritesize_shift*/
unsignedinterasesize_mask;
unsignedintwritesize_mask;
//Kernel-onlystuffstartshere.
constchar*name;
intindex;
/*ecclayoutstructurepointer-readonly!*/
structnand_ecclayout*ecclayout;//eec布局結(jié)構(gòu)
/*Dataforvariableeraseregions.Ifnumeraseregionsiszero,
*itmeansthatthewholedevicehaserasesizeasgivenabove.
*/
intnumeraseregions;//擦除區(qū)域個(gè)數(shù)，通常為1
structmtd_erase_region_info*eraseregions;//擦除區(qū)域的區(qū)域信息地址
/*
*Eraseisanasynchronousoperation.Devicedriversaresupposed
*tocallinstr->callback()whenevertheoperationcompletes,even
*ifitcompleteswithafailure.
*Callersaresupposedtopassacallbackfunctionandwaitforit
*tobecalledbeforewritingtotheblock.
*/
int(*erase)(structmtd_info*mtd,structerase_info*instr);//函數(shù)指針，erase函數(shù)的功能是將一個(gè)erase_info加入擦除隊(duì)列
/*ThisstuffforeXecute-In-Place*/
/*physisoptionalandmaybesettoNULL*/
int(*point)(structmtd_info*mtd,loff_tfrom,size_tlen,
size_t*retlen,void**virt,resource_size_t*phys);//point函數(shù)功能是允許片內(nèi)執(zhí)行（XIP）
/*WeprobablyshouldntallowXIPiftheunpointisntaNULL*/
void(*unpoint)(structmtd_info*mtd,loff_tfrom,size_tlen);//unpoint函數(shù)與point函數(shù)相反，是禁止片內(nèi)執(zhí)行（XIP）
/*AllowNOMMUmmap()todirectlymapthedevice(ifnotNULL)
*-returntheaddresstowhichtheoffsetmaps
*-return-ENOSYStoindicaterefusaltodothemapping
*/
//如果不是NULL，則允許無(wú)MMU單元的地址映射，返回偏移地址
unsignedlong(*get_unmapped_area)(structmtd_info*mtd,
unsignedlonglen,
unsignedlongoffset,
unsignedlongflags);
/*Backingdevicecapabilitiesforthisdevice
*-providesmmapcapabilities
*/
structbacking_dev_info*backing_dev_info;
//MTD設(shè)備的讀寫(xiě)函數(shù)
int(*read)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
int(*write)(structmtd_info*mtd,loff_tto,size_tlen,size_t*retlen,constu_char*buf);
/*Inblackboxflightrecorderlikescenarioswewanttomakesuccessful
writesininterruptcontext.panic_write()isonlyintendedtobe
calledwhenitsknownthekernelisabouttopanicandweneedthe
writetosucceed.Sincethekernelisnotgoingtoberunningformuch
longer,thisfunctioncanbreaklocksanddelaytoensurethewrite
succeeds(butnotsleep).*/
int(*panic_write)(structmtd_info*mtd,loff_tto,size_tlen,size_t*retlen,constu_char*buf);
//用于MTD設(shè)備的OBB數(shù)據(jù)讀寫(xiě)
int(*read_oob)(structmtd_info*mtd,loff_tfrom,
structmtd_oob_ops*ops);
int(*write_oob)(structmtd_info*mtd,loff_tto,
structmtd_oob_ops*ops);
/*
*Methodstoaccesstheprotectionregisterarea,presentinsome
*flashdevices.Theuserdataisonetimeprogrammablebutthe
*factorydataisreadonly.
*/
int(*get_fact_prot_info)(structmtd_info*mtd,structotp_info*buf,size_tlen);
int(*read_fact_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
int(*get_user_prot_info)(structmtd_info*mtd,structotp_info*buf,size_tlen);
int(*read_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
int(*write_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen,size_t*retlen,u_char*buf);
int(*lock_user_prot_reg)(structmtd_info*mtd,loff_tfrom,size_tlen);
/*kvec-basedread/writemethods.
NB:Thecountparameteristhenumberof_vectors_,eachof
whichcontainsan(ofs,len)tuple.
*/
int(*writev)(structmtd_info*mtd,conststructkvec*vecs,unsignedlongcount,loff_tto,size_t*retlen);
/*Sync*/
//MTD設(shè)備的同步函數(shù)
void(*sync)(structmtd_info*mtd);
/*Chip-supporteddevicelocking*/
//芯片的加鎖和解鎖
int(*lock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
int(*unlock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
/*PowerManagementfunctions*/
//支持電源管理函數(shù)
int(*suspend)(structmtd_info*mtd);
void(*resume)(structmtd_info*mtd);
/*Badblockmanagementfunctions*/
//壞塊管理函數(shù)
int(*block_isbad)(structmtd_info*mtd,loff_tofs);
int(*block_markbad)(structmtd_info*mtd,loff_tofs);
structnotifier_blockreboot_notifier;/*defaultmodebeforereboot*/
/*ECCstatusinformation*/
structmtd_ecc_statsecc_stats;//ECC狀態(tài)信息
/*Subpageshift(NAND)*/
intsubpage_sft;
void*priv;//私有數(shù)據(jù)指針
structmodule*owner;
structdevicedev;
intusecount;//記錄用戶的個(gè)數(shù)
/*Ifthedriverissomethingsmart,likeUBI,itmayneedtomaintain
*itsownreferencecounting.Thebelowfunctionsareonlyfordriver.
*Thedrivermayregisteritscallbacks.Thesecallbacksarenot
*supposedtobecalledbyMTDusers*/
//驅(qū)動(dòng)回調(diào)函數(shù)
int(*get_device)(structmtd_info*mtd);
void(*put_device)(structmtd_info*mtd);
};