[U-Boot] dtb vs. kernel command line arguments

[U-Boot] dtb vs. kernel command line arguments

[Curt Brune]

Hello -

I want to pass a number of arguments from u-boot to the booted kernel. 
The arguments are needed by user space applications, not the kernel.

I can think of two ways:

1. append args by setting "bootargs".
2. add nodes to the dtb before booting.

Is there a preferred way to pass information like this?

Like I said the arguments are not needed by the kernel device drivers, 
but by user space applications.

I like the structure of nodes in the dtb.

Cheers,
Curt

[U-Boot] dtb vs. kernel command line arguments

[Kim Phillips]

On Mon, 4 Mar 2013 10:30:45 -0800
Curt Brune <curt@cumulusnetworks.com> wrote:

> Hello -
> 
> I want to pass a number of arguments from u-boot to the booted kernel. 
> The arguments are needed by user space applications, not the kernel.
> 
> I can think of two ways:
> 
> 1. append args by setting "bootargs".
> 2. add nodes to the dtb before booting.
> 
> Is there a preferred way to pass information like this?
> 
> Like I said the arguments are not needed by the kernel device drivers, 
> but by user space applications.
> 
> I like the structure of nodes in the dtb.

please don't dual-purpose device trees as a mechanism of getting
arguments through the kernel into userspace - device trees strictly
describe the hardware.

btw, this question would be more appropriately posted on
devicetree-discuss (in case you have more).

Kim

[U-Boot] dtb vs. kernel command line arguments

[Simon Glass]

Hi Kim,

On Mon, Mar 4, 2013 at 4:03 PM, Kim Phillips <kim.phillips@freescale.com> wrote:
> On Mon, 4 Mar 2013 10:30:45 -0800
> Curt Brune <curt@cumulusnetworks.com> wrote:
>
>> Hello -
>>
>> I want to pass a number of arguments from u-boot to the booted kernel.
>> The arguments are needed by user space applications, not the kernel.
>>
>> I can think of two ways:
>>
>> 1. append args by setting "bootargs".
>> 2. add nodes to the dtb before booting.
>>
>> Is there a preferred way to pass information like this?
>>
>> Like I said the arguments are not needed by the kernel device drivers,
>> but by user space applications.
>>
>> I like the structure of nodes in the dtb.
>
> please don't dual-purpose device trees as a mechanism of getting
> arguments through the kernel into userspace - device trees strictly
> describe the hardware.

That's certainly the primary purpose, but it is also true that the
device tree is a convenient way to pass things to the kernel. It is in
fact becoming the only way on ARM systems. We certainly use it to pass
general information to the kernel, for example the command line.

Regards,
Simon

>
> btw, this question would be more appropriately posted on
> devicetree-discuss (in case you have more).
>
> Kim
>
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot

[U-Boot] dtb vs. kernel command line arguments

[Tom Rini]

On Tue, Mar 05, 2013 at 11:16:17AM -0800, Simon Glass wrote:
> Hi Kim,
> 
> On Mon, Mar 4, 2013 at 4:03 PM, Kim Phillips <kim.phillips@freescale.com> wrote:
> > On Mon, 4 Mar 2013 10:30:45 -0800
> > Curt Brune <curt@cumulusnetworks.com> wrote:
> >
> >> Hello -
> >>
> >> I want to pass a number of arguments from u-boot to the booted kernel.
> >> The arguments are needed by user space applications, not the kernel.
> >>
> >> I can think of two ways:
> >>
> >> 1. append args by setting "bootargs".
> >> 2. add nodes to the dtb before booting.
> >>
> >> Is there a preferred way to pass information like this?
> >>
> >> Like I said the arguments are not needed by the kernel device drivers,
> >> but by user space applications.
> >>
> >> I like the structure of nodes in the dtb.
> >
> > please don't dual-purpose device trees as a mechanism of getting
> > arguments through the kernel into userspace - device trees strictly
> > describe the hardware.
> 
> That's certainly the primary purpose, but it is also true that the
> device tree is a convenient way to pass things to the kernel. It is in
> fact becoming the only way on ARM systems. We certainly use it to pass
> general information to the kernel, for example the command line.

And there, historically, is the answer.  You pass it in via the
command line and parse that at run-time.  So you can use that existing
part of the device tree.

-- 
Tom
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[U-Boot] dtb vs. kernel command line arguments

[Wolfgang Denk]

Dear Simon,

In message <CAPnjgZ3APwSJZV7zPe+b8A58zu-dxHdRGLcyiWHCm6dqQyFH3g@mail.gmail.com> you wrote:
> 
> > please don't dual-purpose device trees as a mechanism of getting
> > arguments through the kernel into userspace - device trees strictly
> > describe the hardware.
> 
> That's certainly the primary purpose, but it is also true that the
> device tree is a convenient way to pass things to the kernel. It is in
> fact becoming the only way on ARM systems. We certainly use it to pass
> general information to the kernel, for example the command line.

I think Kim is right in pointing out that this was given the name
DEVICE tree for a reason - it's not being called "general purpose
information tree".

You may be right that it's a convenient way to pass information to the
kernel - ut note that the original question said: "The arguments are
needed by user space applications, not the kernel."  I think using the
kernel command line here ins more appropriate.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"An organization dries up if you don't challenge it with growth."
       - Mark Shepherd, former President and CEO of Texas Instruments

Re: [U-Boot] dtb vs. kernel command line arguments

[Grant Likely]

On Mon, 4 Mar 2013 18:03:23 -0600, Kim Phillips <kim.phillips-KZfg59tc24xl57MIdRCFDg@public.gmane.org> wrote:
> On Mon, 4 Mar 2013 10:30:45 -0800
> Curt Brune <curt-qUQiAmfTcIp+XZJcv9eMoEEOCMrvLtNR@public.gmane.org> wrote:
> 
> > Hello -
> > 
> > I want to pass a number of arguments from u-boot to the booted kernel. 
> > The arguments are needed by user space applications, not the kernel.
> > 
> > I can think of two ways:
> > 
> > 1. append args by setting "bootargs".
> > 2. add nodes to the dtb before booting.
> > 
> > Is there a preferred way to pass information like this?
> > 
> > Like I said the arguments are not needed by the kernel device drivers, 
> > but by user space applications.
> > 
> > I like the structure of nodes in the dtb.
> 
> please don't dual-purpose device trees as a mechanism of getting
> arguments through the kernel into userspace - device trees strictly
> describe the hardware.

Why not? The chosen node in particular is for software configuration. I
don't have any problem with passing U-Boot extra data through the chosen
node. Just don't go crazy and please document it.

g.

[U-Boot] dtb vs. kernel command line arguments

[Grant Likely]

On Mon, 4 Mar 2013 18:03:23 -0600, Kim Phillips <kim.phillips@freescale.com> wrote:
> On Mon, 4 Mar 2013 10:30:45 -0800
> Curt Brune <curt@cumulusnetworks.com> wrote:
> 
> > Hello -
> > 
> > I want to pass a number of arguments from u-boot to the booted kernel. 
> > The arguments are needed by user space applications, not the kernel.
> > 
> > I can think of two ways:
> > 
> > 1. append args by setting "bootargs".
> > 2. add nodes to the dtb before booting.
> > 
> > Is there a preferred way to pass information like this?
> > 
> > Like I said the arguments are not needed by the kernel device drivers, 
> > but by user space applications.
> > 
> > I like the structure of nodes in the dtb.
> 
> please don't dual-purpose device trees as a mechanism of getting
> arguments through the kernel into userspace - device trees strictly
> describe the hardware.

Why not? The chosen node in particular is for software configuration. I
don't have any problem with passing U-Boot extra data through the chosen
node. Just don't go crazy and please document it.

g.