Re: [PATCH 1/3] ARM: omap_device: handle first time activation of console device

Cousson, Benoit
2011-11-16T15:14:55Z

Hi Rob,

On 11/16/2011 3:50 PM, Rob Herring wrote:
> On 11/16/2011 05:02 AM, Rajendra Nayak wrote:
>> console device on OMAP is never reset or idled by hwmod post
>> initial setup, early during boot, for obvious reasons not to
>> break early debug prints thrown on console.
>> This leaves the console device enabled at boot and the first activation
>> of it using hwmod needs to be handled in such a way that a disable is
>> called followed by an enable of the hwmod, the subsequent activations
>> can then use the default activation technique.
>>
>> To handle this add a new binding to identify a hwmod which is used as
>> the console device.
>>
>> This patch is based on the what is done in serial.c for non-DT builds.
>>
>> Signed-off-by: Rajendra Nayak<rnayak@ti.com>
>> ---
>> .../devicetree/bindings/arm/omap/omap.txt | 1 +
>> arch/arm/plat-omap/omap_device.c | 33 +++++++++++++++++++-
>> 2 files changed, 33 insertions(+), 1 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/omap/omap.txt b/Documentation/devicetree/bindings/arm/omap/omap.txt
>> index dbdab40..46ffd41 100644
>> --- a/Documentation/devicetree/bindings/arm/omap/omap.txt
>> +++ b/Documentation/devicetree/bindings/arm/omap/omap.txt
>> @@ -21,6 +21,7 @@ Required properties:
>> Optional properties:
>> - ti,no_idle_on_suspend: When present, it prevents the PM to idle the module
>> during suspend.
>> +- ti,console_hwmod: boolean, identifies the hwmod used as console device
>>
>
> This doesn't seem right. Which console is not a h/w property. Why can't
> you use aliases like other platforms are doing?
>
> Also, it's not clear in the documentation where this (and
> ti,no_idle_on_suspend) should go in the DT. Both seem like they should
> be kernel cmdline params.

That raise the question about using DT to pass linux specific parameter.
We already discuss that on the mailing list, but never get a clear answer.
It seems that DT is already used to provide some OS specific information
using the "linux," prefix for example.

There are clearly a couple of parameters that can be provided by the
bootloader, but that does not reflect a HW property.

So what is the guideline for that, should we stick to cmdline params for
that?

Quoting Grant's documentation, runtime configuration is supported:

"Runtime configuration

In most cases, a DT will be the sole method of communicating data from
firmware to the kernel, so also gets used to pass in runtime and
configuration data like the kernel parameters string and the location of
an initrd image.

Most of this data is contained in the /chosen node, and when booting
Linux it will look something like this:

chosen {
bootargs = "console=ttyS0,115200 loglevel=8";
initrd-start = <0xc8000000>;
initrd-end = <0xc8200000>;
};

The bootargs property contains the kernel arguments, and the initrd-*
properties define the address and size of an initrd blob. The chosen
node may also optionally contain an arbitrary number of additional
properties for platform-specific configuration data."

Does that mean that this is supported only if the bootloader does not
support cmdline?

Thanks,
Benoit