Re: ARM kernel parameters

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 22.12.2013 20:41, Leif Lindholm wrote:
> 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.
> 
And override initrd tag. That what trunk currently does: appends
parameters and overrides initrd tag.
> 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.
But wouldn't it be overriden by later explicit parameter supplied from
command line?
> 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
> 
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