Hi Mike, On Wed, Nov 12, 2014 at 09:45:58PM -0800, Mike Thompson wrote:
I'm working on a port the latest Linux kernel to a Nuvoton N32905 - a very inexpensive ARM9 based SoC similar to the Freescale iMX23 in many respects. My hope is that my code for this SoC will eventually reach the mainline kernel, but the whole process a fairly daunting task to a kernel newbie such as myself.
Been there... :)
I do have a six year old port of the 2.6.35 kernel to this SoC to help as a reference, but it's pretty much a rewrite to support devicetree, the common clock framework, and a myriad of changes needed to get a new SoC supported in the mainline kernel. Not to mention all the 2.6.35 code added for this chip isn't even close to the coding standards for the Kernel.
So far I got the 3.17 kernel running pretty well the baseline peripherals such as clocks, interrupt controller, UART, GPIO & pin muxing along with hire level peripherals such as MMC/SD card support, MTD NAND and NOR flash and USB host support.
Cool!
As a guide, I've been using other ARM SoCs for examples and a number of very useful presentations on ARM SoC support from the Free Electron folks. Although presentations such as the "ARM SoC Linux Support Check-list" are very useful, they don't go into much detail.
My question is two fold. Is there detailed information of all the things that need to be covered in the code to introduce a new ARM SoC into the kernel?
Usually "enough so that it boots", which means: timers, interrupts, UARTs, and that's pretty much it. Any additional feature is of course welcome, but I'd suggest to just post that for the first set of patches. There will probably significant changes to make to your base drivers (and I would include clocks and pinctrl into these drivers), and these will impact any further developments. You don't want to have too much dependency :) Start small, then build on top of what's accepted.
Then, is there a description of how I start to go about contributing support for this chip into the Linux kernel? I honestly don't really know where to begin.
Like I said, send the minimum amount of patches to have Linux boot an initramfs on your SoC. Apart from that, there is nothing out of the ordinary on how to submit patches, everything is detailed in Documentation/SubmittingPatches. Basically, it will involve sending patches to the linux-arm-kernel mailing list and the ARM SoC kernel maintainers. Make sure that everything has no warning in scripts/checkpatch.pl, and you're good to go. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com