Re: introduce device_is_attached()

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On 04/16/12 19:37, David Young wrote:
> On Mon, Apr 16, 2012 at 06:52:28PM +0200, Christoph Egger wrote:
> > Hi,
> >
> > I want to introduce a new function to sys/devices.h:
> >
> > bool device_is_attached(device_t parent, cfdata_t cf);
> >
> > The purpose is for bus drivers who wants to attach children
> > and ensure that only one instance of it will attach.
> >
> > 'parent' is the bus driver and 'cf' is the child device
> > as passed to the submatch callback via config_search_loc().
> >
> > The return value is true if the child is already attached.
> >
> > I implemented a reference usage of it in amdnb_misc.c to ensure
> > that amdtemp only attaches once on rescan.
>
> Don't add that function.  Just use a small amdnb_misc softc to track
> whether or not the amdtemp is attached or not:
>
> struct amdnb_misc_softc {
>         device_t sc_amdtemp;
> };

This is what pchb(4) did before the revert. It doesn't meet the needs
of attaching multiple drivers to the same pci device.

> Don't pass a pci_attach_args to amdtemp.  Just pass it the chipset tag
> and PCI tag if that is all that it needs.

Why is pci_attach_args a no-go ?

> I'm not sure I fully understand the purpose of amdnb_miscbus.
> Are all of the functions that do/will attach at amdnb_miscbus
> configuration-space only functions, or are they something else?  Please
> explain what amdnb_miscbus is for.

Drivers attaching to amdnb_miscbus are all pci drivers which use
different capabilities of the northbridge device.
Their match/attach routines need the same 'aux' parameter as it
is passed to amdnb_misc(4).

amdtemp(4) uses some PCI registers of the northbridge device to read
the cpu temperature.
I have a local driver which uses a different feature of the same
northbridge device.
To access the device I need the same chipset tag and pci tag.

Instead of making amdtemp(4) a mess I chose to implement different
features in different small drivers.
This also simplifies handling of erratas: If a feature doesn't work
then just don't let match/attach the corresponding driver.

Christoph