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i.MX Processors Knowledge Base

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Recently, some customers are using i.MX processor, they want to add raid & LVM function support to the kernel, but they have encountered the problem that the compilation cannot pass. Tested it in L4.14.98, L4.19.35 & L5.4.x, Only L4.14.98 bsp exists the problem. Here are the experimental steps I have done, including the same problems I encountered with the customer, and how to modify the kernel to ensure that the compilation passes. 1. Exporting cross compilation tool chain from yocto BSP (1) Downloading Yocto BSP and compiling it. Following steps in i.MX_Yocto_Project_User's_Guide.pdf, download Yocto BSP and compile it successfully. (2) Exporting cross compilation tool chain Following methods described in i.MX_Linux_User's_Guide.pdf, export cross compilation tool chain from yocto BSP. See Chapter 4.5.12 of the document, please! Then cross compilation tool chain will be like below: (3) Copying linux BSP source code to a new directory # cd ~ # mkdir L4.14.98-2.0.0 # cd L4.14.98-2.0.0 # cp -r ~/imx-yocto-bsp/build-fb/tmp/work/imx6qsabresd-poky-linux-gnueabi/linux-imx/4.14.98- r0/git ./ Then all linux source code has been copied to L4.14.98-2.0.0, which is the top directory of linux kernel source code, I will compile kernel image here. 2. Compiling linux kernel # cd ~/L4.14.98-2.0.0 # source /opt/fsl-imx-fb/4.14-sumo/environment-setup-cortexa9hf-neon-poky-linux-gnueabi # export ARCH=arm # make imx_v7_defconfig # make menuconfig Then we will add RAID and LVM modules to linux kernel. In order to reproduce errors, I added all related modules to kernel. See below, please! Device drivers---->Multiple devices driver support (RAID and LVM) After save and exit, began to compile kernel. # make (make –j4) The following errors will occur: ------------------------------------------------------------------------------------------- drivers/md/dm-rq.c: In function ‘dm_old_init_request_queue’: drivers/md/dm-rq.c:716:2: error: implicit declaration of function ‘elv_register_queue’; did you mean ‘blk_register_queue’? [-Werror=implicit-function-declaration] elv_register_queue(md->queue); ^~~~~~~~~~~~~~~~~~ blk_register_queue cc1: some warnings being treated as errors scripts/Makefile.build:326: recipe for target 'drivers/md/dm-rq.o' failed make[2]: *** [drivers/md/dm-rq.o] Error 1 scripts/Makefile.build:585: recipe for target 'drivers/md' failed make[1]: *** [drivers/md] Error 2 Makefile:1039: recipe for target 'drivers' failed make: *** [drivers] Error 2 ------------------------------------------------------------------------------------------- 3. Finding out root cause and solving it (1) elv_register_queue( ) function The function is loaded in dm-rq.c : int dm_old_init_request_queue(struct mapped_device *md, struct dm_table *t) { … … elv_register_queue(md->queue); … … } BUT compiler didn’t find it’s declaration and entity. Searching source code, and found it declared in linux_top/block/blk.h: … … int elv_register_queue(struct request_queue *q); … … It’s entity is in linux_top/block/elevator.c: int elv_register_queue(struct request_queue *q) { … … } (2) Adding declaration and exporting the function --- Declaration Add the line below to dm-rq.c: … … extern int elv_register_queue(struct request_queue *q); … … --- Exporting the function(elevator.c) Add EXPORT_SYMBOL(elv_register_queue); to the end of function, see below. int elv_register_queue(struct request_queue *q) { … … } EXPORT_SYMBOL(elv_register_queue); 4. Re-compiling Linux Kernel The above error will not occur and the compilation will complete successfully.   NXP CAS team Weidong Sun
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