Re: [Qemu-devel] [PATCH 0/2] Add get_dev_path callback to ISA bus.

[Markus Armbruster]

Gleb Natapov <address@hidden> writes:

> On Tue, Oct 26, 2010 at 11:57:53AM +0200, Markus Armbruster wrote:
>> Gleb Natapov <address@hidden> writes:
>> 
>> > On Mon, Oct 25, 2010 at 07:53:41PM +0200, Markus Armbruster wrote:
>> >> Gleb Natapov <address@hidden> writes:
>> >> 
>> >> > On Mon, Oct 25, 2010 at 05:10:15PM +0200, Markus Armbruster wrote:
>> >> >> Gleb Natapov <address@hidden> writes:
>> >> >> 
>> >> >> > PCI bus already has one. For ISA bus this patch series uses device's
>> >> >> > ioports to uniquely describe it. For isa-ide, for example, 
>> >> >> > get_dev_path
>> >> >> > method returns:
>> >> >> > 01f0-01f7,03f6 for first IDE controller
>> >> >> > 0170-0177,0376 for second one
>> >> >> 
>> >> >> Any I/O port used by the device identifies it.  I'd say a common
>> >> >> identifier is the "I/O base", the lowest I/O port used.
>> >> > So use only first port from the string. More information is better then
>> >> > less information. You can always drop information you do not need.
>> >> 
>> >> I'd prefer canonical bus addresses to be terse.  It's not the place to
>> >> give additional information.
>> >
>> > I'd prefer them to give full info but not more. I don't see why you
>> > point is more valid then mine.
>> 
>> Full information about ISA resources is more than I/O ports, it also
>> includes IRQs and DMA channels.
> So you are arguing to add more info there? :) Theoretically there is
> nothing that prevents ISA devices from sharing IRQ line (existing ISA
> devices just not built to do that and nobody produces new once) and
> DMA is separate device on ISA bus AFAIK.
>
>> 
>> An address is not the place to give full information.  The purpose of an
>> address is to name a thing, not to give full information about that
>> thing.
>> 
> Address should contain info that allows to find device easily. If
> whoever looking for a device knows only one port device is using he
> will not find the device if we'll use different port to name it. May be
> not the problem in practice.

If he knows only one port, he can't form the address proposed by you.
He needs to know *all* ports.  So what he does is search all the devices
for the one that uses the port in question.  Same for the address I
propose.  The proposal differ for the case where the user remembers just
the base address.  I believe that's the common case.

>> By the way, get_dev_path() really needs a written contract.  Actually,
>> all the qdev and qbus callbacks do.
> What do you mean by that? It should be stable ABI, is this what you
> mean?

A contract between qdev core and the device models, so that device model
authors know what exactly their callback functions are supposed to do.

Stability is a separate matter.  Since it's a purely internal interface,
we don't want it.