Re: ARM kernel parameters

[Leif Lindholm]

On Sun, Dec 22, 2013 at 12:45:22AM +0100, Vladimir 'φ-coder/phcoder' Serbinenko 
wrote:
> Hello, all. I've been able to boot Linux on my raspberry pi, after
> fixing several bugs in loader. But for this I had to have a line like:
> linux /kernel_cutdown.img dma.dmachans=0x???? bcm2708_fb.fbwidth=656
> bcm2708_fb.fbheight=416 bcm2708.boardrev=0xe bcm2708.serial=0x????????
> smsc95xx.macaddr=??:??:??:??:?? dwc_otg.lpm_enable=0
> console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1
> root=/dev/mmcblk0p2 rootfstype=ext4 rootwait

Urgh...

> When using standard bootloader the part
> dma.dmachans=0x???? bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416
> bcm2708.boardrev=0xe bcm2708.serial=0x????????
> smsc95xx.macaddr=??:??:??:??:??
> is added automatically. The part
> dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200
> console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 rootwait
> comes from cmdline.txt.
> 
> It's not possible to tell for sure then one ends and the other starts.
> Does anyone see any problem with prepending the arguments GRUB itself
> received to the kernel command line on all platforms using ATAGs?

The current arm support is heavily geared towards FDT, but permits
ATAGs to be passed on unmodified. Adding the ability to modify the
command line would certainly make sense.

Making the linux command append instead of replace the command line
could make life interesting. If the u-boot bootargs happen to include 
basic options such as root=, then Linux's behaviour may not be obvious.
So while potentially simplifying the life of the user, it also
increases the amount of awareness they need to have over the U-Boot/
GRUB/Linux interaction.

/
    Leif