[SeaBIOS] [RFC PATCH v3 06/19] Implement "-dimm" command line option

Vasilis Liaskovitis vasilis.liaskovitis at profitbricks.com
Mon Sep 24 12:42:43 CEST 2012

On Sat, Sep 22, 2012 at 01:46:57PM +0000, Blue Swirl wrote:
> On Fri, Sep 21, 2012 at 11:17 AM, Vasilis Liaskovitis
> <vasilis.liaskovitis at profitbricks.com> wrote:
> > Example:
> > "-dimm id=dimm0,size=512M,node=0,populated=off"
> There should not be a need to introduce a new top level option,
> instead you should just use -device, like
> -device dimm,base=0,id=dimm0,size=512M,node=0,populated=off
> That would also specify the start address.

What is "base"? the start address? I think the start address should be calculated by the
chipset / board, not by the user.

The "-dimm" option is supposed to specify the dimm/memory layout, and not create
any devices.

If we don't want this new option, I have a question:

A "-device/device_add" means we create a new qdev device at startup or as a
hotplug operation respectively. So, the semantics of 
"-device dimm,id=dimm0,size=512M,node=0,populated=on" are clear to me.

What does "-device dimm,populated=off" mean from a qdev perspective? There are 2

- The device is created on the dimmbus, but is not used/populated yet. Than the
activation/acpi-hotplug of the dimm may require a separate command (we used to have
"dimm_add" in versions < 3). "device_add" handling always hotplugs a new qdev
device, so this wouldn't fit this usecase, because the device already exists. In
this case, the actual "acpi hotplug" operation is decoupled from qdev device

- The dimmdevice is not created when "-device dimm,populated=off" (this would
require some ugly checking in normal -device argument handling). Only the dimm
layout is saved. The hotplug is triggered from a normal device_add later. So in
this case, the "acpi hotplug" happens at the same time as the qdev hotplug.

Do you see a simpler alternative without introducing a new option?

Using the "-dimm" option follows the second semantic and avoids changing the "-device"
semantics. Dimm layout description is decoupled from dimmdevice creation, and qdev
hotplug coincides with acpi hotplug.


- Vasilis

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