Overriding/concatenating kernel command-line with bootargs from dtb?

Overriding/concatenating kernel command-line with bootargs from dtb?

[Florian Fainelli]

Hi all,

I have a specific use case, where two boards using the same SoC have different 
UART speeds, which is something that I have specified in their corresponding 
dts files. In order to make sure people don't mess up the configuration, I 
prefer not to rely on the bootloader-supplied kernel-command line.

I was kind of expecting that ARM_ATAG_DTB_COMPAT + CMDLINE_EXTEND would 
actually concatenate the kernel command-line with the bootargs provided from 
dtb.

Is this something someone else would need? If so, shall we just make that 
happen when the two config symbols mentionned above are enabled, or shall we 
introduce a 4th kernel command line handling strategy?

Thank you for your answers.
-- 
Florian

Re: Overriding/concatenating kernel command-line with bootargs from dtb?

[Nicolas Pitre]

On Fri, 8 Jun 2012, Florian Fainelli wrote:

> Hi all,
> 
> I have a specific use case, where two boards using the same SoC have different 
> UART speeds, which is something that I have specified in their corresponding 
> dts files. In order to make sure people don't mess up the configuration, I 
> prefer not to rely on the bootloader-supplied kernel-command line.
> 
> I was kind of expecting that ARM_ATAG_DTB_COMPAT + CMDLINE_EXTEND would 
> actually concatenate the kernel command-line with the bootargs provided from 
> dtb.
> 
> Is this something someone else would need? If so, shall we just make that 
> happen when the two config symbols mentionned above are enabled, or shall we 
> introduce a 4th kernel command line handling strategy?

The former please.  The logic in parse_tag_cmdline() needs to be 
duplicated in early_init_dt_scan_chosen().  CONFIG_CMDLINE_FORCE is 
already implemented, so only CONFIG_CMDLINE_EXTEND is missing.


Nicolas

Re: Overriding/concatenating kernel command-line with bootargs from dtb?

[Rob Herring]

On 06/08/2012 02:55 AM, Florian Fainelli wrote:
> Hi all,
> 
> I have a specific use case, where two boards using the same SoC have different 
> UART speeds, which is something that I have specified in their corresponding 
> dts files. In order to make sure people don't mess up the configuration, I 
> prefer not to rely on the bootloader-supplied kernel-command line.
> 
> I was kind of expecting that ARM_ATAG_DTB_COMPAT + CMDLINE_EXTEND would 
> actually concatenate the kernel command-line with the bootargs provided from 
> dtb.
> 
> Is this something someone else would need? If so, shall we just make that 
> happen when the two config symbols mentionned above are enabled, or shall we 
> introduce a 4th kernel command line handling strategy?
> 
> Thank you for your answers.

There was a patch to do this:

http://www.mail-archive.com/devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org/msg10448.html

Please comment if this works for you.

Rob

Re: Overriding/concatenating kernel command-line with bootargs from dtb?

[Florian Fainelli]

Hi Rob,

On Monday 11 June 2012 09:34:33 Rob Herring wrote:
> On 06/08/2012 02:55 AM, Florian Fainelli wrote:
> > Hi all,
> > 
> > I have a specific use case, where two boards using the same SoC have 
different 
> > UART speeds, which is something that I have specified in their 
corresponding 
> > dts files. In order to make sure people don't mess up the configuration, I 
> > prefer not to rely on the bootloader-supplied kernel-command line.
> > 
> > I was kind of expecting that ARM_ATAG_DTB_COMPAT + CMDLINE_EXTEND would 
> > actually concatenate the kernel command-line with the bootargs provided 
from 
> > dtb.
> > 
> > Is this something someone else would need? If so, shall we just make that 
> > happen when the two config symbols mentionned above are enabled, or shall 
we 
> > introduce a 4th kernel command line handling strategy?
> > 
> > Thank you for your answers.
> 
> There was a patch to do this:
> 
> http://www.mail-archive.com/devicetree-
discuss@lists.ozlabs.org/msg10448.html
> 
> Please comment if this works for you.

This patch indeeds work fine for me when I disable ARM_ATAG_DTB_COMPAT. If I 
let it turned on the chosen node is correctly scanned, but its value, is the 
one coming from tag_cmdline() which is actually the bootloader supplied 
commad-line. I will cook up a patch for this, because I expect the 3 command-
lines to be concatened in the end (built-in, atag and dtb).

I don't see any comments from Ben or anyone after Doug sent his version 2 of 
the patch, is there any reason not to merge it?
-- 
Florian