ARM-Linux驱动--MTD驱动分析(一)

作者：时间：2016-11-20 来源：网络收藏

主机：Gentoo Linux 11.2 with linux kernel 3.0.6

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

本文引用地址：//m.amcfsurvey.com/article/201611/319012.htm

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

structmtd_info{
u_chartype;//内存技术类型，例如MTD_RAM,MTD_ROM,MTD_NORFLASH,MTD_NAND_FLASH,MTD_PEROM等
uint32_tflags;//标志位
uint64_tsize;//TotalsizeoftheMTD//MTD设备的大小
/*"Major"erasesizeforthedevice.Naïveusersmaytakethis
*tobetheonlyerasesizeavailable,ormayusethemoredetailed
*informationbelowiftheydesire
*/
uint32_terasesize;//最小的擦除块大小
/*Minimalwritableflashunitsize.IncaseofNORflashitis1(even
*thoughindividualbitscanbecleared),incaseofNANDflashitis
*oneNANDpage(orhalf,orone-fourthsofit),incaseofECC-edNOR
*itisofECCblocksize,etc.Itisillegaltohavewritesize=0.
*Anydriverregisteringastructmtd_infomustensureawritesizeof
*1orlarger.
*/
uint32_twritesize;//编程块大小
uint32_toobsize;//AmountofOOBdataperblock(e.g.16)//oob(Outofband)块大小
uint32_toobavail;//AvailableOOBbytesperblock//每块的可用的oob字节
/*
*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布局结构
/*Dataforvariableeraseregions.Ifnumeraseregionsiszero,
*itmeansthatthewholedevicehaserasesizeasgivenabove.
*/
intnumeraseregions;//擦除区域个数，通常为1
structmtd_erase_region_info*eraseregions;//擦除区域的区域信息地址
/*
*Eraseisanasynchronousoperation.Devicedriversaresupposed
*tocallinstr->callback()whenevertheoperationcompletes,even
*ifitcompleteswithafailure.
*Callersaresupposedtopassacallbackfunctionandwaitforit
*tobecalledbeforewritingtotheblock.
*/
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
/*ThisstuffforeXecute-In-Place*/
/*physisoptionalandmaybesettoNULL*/
int(*point)(structmtd_info*mtd,loff_tfrom,size_tlen,
size_t*retlen,void**virt,resource_size_t*phys);//point函数功能是允许片内执行（XIP）
/*WeprobablyshouldntallowXIPiftheunpointisntaNULL*/
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）
/*AllowNOMMUmmap()todirectlymapthedevice(ifnotNULL)
*-returntheaddresstowhichtheoffsetmaps
*-return-ENOSYStoindicaterefusaltodothemapping
*/
//如果不是NULL，则允许无MMU单元的地址映射，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设备的读写函数
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设备的OBB数据读写
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设备的同步函数
void(*sync)(structmtd_info*mtd);
/*Chip-supporteddevicelocking*/
//芯片的加锁和解锁
int(*lock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
int(*unlock)(structmtd_info*mtd,loff_tofs,uint64_tlen);
/*PowerManagementfunctions*/
//支持电源管理函数
int(*suspend)(structmtd_info*mtd);
void(*resume)(structmtd_info*mtd);
/*Badblockmanagementfunctions*/
//坏块管理函数
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状态信息
/*Subpageshift(NAND)*/
intsubpage_sft;
void*priv;//私有数据指针
structmodule*owner;
structdevicedev;
intusecount;//记录用户的个数
/*Ifthedriverissomethingsmart,likeUBI,itmayneedtomaintain
*itsownreferencecounting.Thebelowfunctionsareonlyfordriver.
*Thedrivermayregisteritscallbacks.Thesecallbacksarenot
*supposedtobecalledbyMTDusers*/
//驱动回调函数
int(*get_device)(structmtd_info*mtd);
void(*put_device)(structmtd_info*mtd);
};