"Pandita, Vikram" <vikram.pandita@xxxxxx> writes: >>Vikram Pandita wrote: >>> This patch cleans up the DEBUG_LL infrastructure for omap boards. >> >>Thanks Vikram, this is indeed in need of some cleanup. But I have some >>comments about the approach taken. >> >>This approach still doesn't solve one of the fundamental problems with >>the current implementation. It prevents using a single kernel across >>multiple boards. If we could drop the compile-time decision in favor of >>a runtime one based on machine-type, we could use a single base >>defconfig that would be able to be tested on all omap3 boards for example. >> >>For the zImage UART output (uncompress.h) there is a global variable >>__machine_arch_type which could be used to check the board type and set >>variable for UART base and shift. We do this on DaVinci. > > Could you give reference to this code on DaVinci? http://git.kernel.org/?p=linux/kernel/git/khilman/linux-davinci.git;a=blobdiff;f=arch/arm/mach-davinci/include/mach/uncompress.h;h=0f1f12b67875f86232c0e06e1a687a6d7f19b18a;hp=1e27475f9a2322f1a4f61e25fd1a1e5858e29fc2;hb=bb9647f44b091ebff17f400bb2a468c7e419f3ac;hpb=0dc6306a65f30c0483cfed9b3e8ee1eb3d093e84 > > Yes this is doable, but the question is, how do we pass these variables to the kernel start: > arch/arm/kernel/head.S > > First stage, arch/arm/boot/compressed/head.S gets the arch type -> shift/uart-addr. Fine. > This stage ends with relocated code over righting the decompressor. > > Second stage, arch/arm/kernel/head.S now starts. > > I am not sure how to share the data from Stage 1 in this stage? This is already taken care of. The zImage boot passes the machine-type in a register, then arch/arm/kernel/head.S uses that to decide which machine to start. This is where the MACHINE_START/MACHINE_END macros come in to define the machine-specific hooks called at boot time. You should use one of the early machine hooks (probably .map_io) to to set the UART base and shift for the board. The catch is that between the start of the head.S code and the mach->map_io hook, printascii() may be called and use the debug macros to try to print out chars. Care must be taken that if the UART is not yet known/defined, nothing is printed. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
