ACPI and the PNP Layer

ACPI and the PNP Layer

[Dino Klein]

Hello everyone,
I am curious to know whether there is supposed to be a relationship between 
ACPI and the PNP layer in Linux, i.e. should the devices found through ACPI 
be registered with the PNP layer, or will the PNP layer itself be supplanted 
on ACPI based machines?

The reason I'm asking is because I'm toying with the idea of writing a 
protocol driver that will "export" devices from ACPI to the PNP layer. Would 
this be a more "proper" scheme of dealing with devices, instead of having 
each driver modified to register with the ACPI bus (serial driver style)? 
Wouldn't placing devices in the PNP layer make it more transparent for 
drivers to bind to devices, whether the machine supports ACPI, or only 
PNPBIOS?

Thanks.

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Re: ACPI and the PNP Layer

[Matthew Wilcox]

On Sun, Feb 01, 2004 at 12:28:27AM +0000, Dino Klein wrote:
> I am curious to know whether there is supposed to be a relationship between 
> ACPI and the PNP layer in Linux, i.e. should the devices found through ACPI 
> be registered with the PNP layer, or will the PNP layer itself be 
> supplanted on ACPI based machines?

PNP is unnecessary on machines with ACPI.

> The reason I'm asking is because I'm toying with the idea of writing a 
> protocol driver that will "export" devices from ACPI to the PNP layer. 
> Would this be a more "proper" scheme of dealing with devices, instead of 
> having each driver modified to register with the ACPI bus (serial driver 
> style)? Wouldn't placing devices in the PNP layer make it more transparent 
> for drivers to bind to devices, whether the machine supports ACPI, or only 
> PNPBIOS?

I think there's a fundamental mistake here, which is that drivers need
to be modified to deal with ACPI.  The serial driver (I'm the original
author of the 8250_acpi code) needed to be modified to discover serial
devices in the ACPI namespace.  This is because HP's ia64 machines are
legacy-free, so do not have serial ports at 0x3f8 and 0x2f8 (or wherever
...) like PCs.  Some of HP's machines have PCI serial ports which need
no additional code, but others have what are called 'PDH UARTs' which
can only be discovered by looking in the ACPI namespace.

Obviously no ia64 machine will support ISAPNP or PNPBIOS, so your proposal
wouldn't work very well.  It's also not a lot of code -- 4934 bytes for
8250_acpi.c versus 12488 bytes for 8250_pnp.c.  I can't think of any other
"legacy devices in non-legacy positions" situations like this.  Can you?

-- 
"Next the statesmen will invent cheap lies, putting the blame upon 
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain


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Re: ACPI and the PNP Layer

[Dino Klein]

>From: Matthew Wilcox <willy-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org>
>To: Dino Klein <dinoklein-PkbjNfxxIARBDgjK7y7TUQ@public.gmane.org>
>CC: acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
>Subject: Re: [ACPI] ACPI and the PNP Layer
>Date: Sun, 1 Feb 2004 01:43:17 +0000
>
>On Sun, Feb 01, 2004 at 12:28:27AM +0000, Dino Klein wrote:
> > I am curious to know whether there is supposed to be a relationship 
>between
> > ACPI and the PNP layer in Linux, i.e. should the devices found through 
>ACPI
> > be registered with the PNP layer, or will the PNP layer itself be
> > supplanted on ACPI based machines?
>
>PNP is unnecessary on machines with ACPI.

When you say PNP, are you refering to PNPBIOS/ISAPNP, or the Linux PNP Layer 
iself, which uses the previous two as PNP protocols?


> > The reason I'm asking is because I'm toying with the idea of writing a
> > protocol driver that will "export" devices from ACPI to the PNP layer.
> > Would this be a more "proper" scheme of dealing with devices, instead of
> > having each driver modified to register with the ACPI bus (serial driver
> > style)? Wouldn't placing devices in the PNP layer make it more 
>transparent
> > for drivers to bind to devices, whether the machine supports ACPI, or 
>only
> > PNPBIOS?
>
>I think there's a fundamental mistake here, which is that drivers need
>to be modified to deal with ACPI.  The serial driver (I'm the original
>author of the 8250_acpi code) needed to be modified to discover serial
>devices in the ACPI namespace.  This is because HP's ia64 machines are
>legacy-free, so do not have serial ports at 0x3f8 and 0x2f8 (or wherever
>...) like PCs.  Some of HP's machines have PCI serial ports which need
>no additional code, but others have what are called 'PDH UARTs' which
>can only be discovered by looking in the ACPI namespace.

You're saying this under the assumption that everything will go USB/PCI/etc 
in the future, right?


>Obviously no ia64 machine will support ISAPNP or PNPBIOS, so your proposal
>wouldn't work very well.  It's also not a lot of code -- 4934 bytes for
>8250_acpi.c versus 12488 bytes for 8250_pnp.c.  I can't think of any other
>"legacy devices in non-legacy positions" situations like this.  Can you?

I took a quick look at the two files, and they are quite comparable 
code-wise; the additional size in 8250_pnp.c is due to the extra comments 
and EISA IDs defined.
Now about the legacy devices - wouldn't you say that the keyboard/PS2 driver 
should be modified to register with the ACPI bus, just in order to have 
everything nice & neat? or how about the parallel port, or motherboard based 
IRDA (PNP0510)?
Perhaps I'm just exaggerating with this, but I like to have things nice and 
neat :)

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Re: ACPI and the PNP Layer

[Matthew Wilcox]

On Sun, Feb 01, 2004 at 02:41:02AM +0000, Dino Klein wrote:
> >PNP is unnecessary on machines with ACPI.
> 
> When you say PNP, are you refering to PNPBIOS/ISAPNP, or the Linux PNP 
> Layer iself, which uses the previous two as PNP protocols?

The former.

> >I think there's a fundamental mistake here, which is that drivers need
> >to be modified to deal with ACPI.  The serial driver (I'm the original
> >author of the 8250_acpi code) needed to be modified to discover serial
> >devices in the ACPI namespace.  This is because HP's ia64 machines are
> >legacy-free, so do not have serial ports at 0x3f8 and 0x2f8 (or wherever
> >...) like PCs.  Some of HP's machines have PCI serial ports which need
> >no additional code, but others have what are called 'PDH UARTs' which
> >can only be discovered by looking in the ACPI namespace.
> 
> You're saying this under the assumption that everything will go USB/PCI/etc 
> in the future, right?

Correct.  They're cheaper and simpler than the alternatives, so once
support is sufficiently widespread, I would indeed expect the legacy
support to go away.

> >Obviously no ia64 machine will support ISAPNP or PNPBIOS, so your proposal
> >wouldn't work very well.  It's also not a lot of code -- 4934 bytes for
> >8250_acpi.c versus 12488 bytes for 8250_pnp.c.  I can't think of any other
> >"legacy devices in non-legacy positions" situations like this.  Can you?
> 
> I took a quick look at the two files, and they are quite comparable 
> code-wise; the additional size in 8250_pnp.c is due to the extra comments 
> and EISA IDs defined.
> Now about the legacy devices - wouldn't you say that the keyboard/PS2 
> driver should be modified to register with the ACPI bus, just in order to 
> have everything nice & neat? or how about the parallel port, or motherboard 
> based IRDA (PNP0510)?
> Perhaps I'm just exaggerating with this, but I like to have things nice and 
> neat :)

PS/2 is obsoleted by USB, as is parallel.  I don't know abut IRDA but I
would expect it to show up as a PCI device normally.  Are manufacturers
still making machines which have this as a non-PCI device?  Remember just
because it's on the motherboard doesn't mean it's a non-PCI device.

Using the PNP layer on non-x86 would certainly lead to problems today.
For example:

        /* check if the resource is valid */
        if (*irq < 0 || *irq > 15)
                return 0;

I can't see this proposal being a good idea today.  Perhaps if the PNP
layer were cleaned up it would be.  That'd be a good place to direct
your efforts.  For example, could drivers/pnp/resource.c use more of
the facilities in kernel/resource.c?  Should some of the features from
pnp/resource.c be moved to kernel/resource.c?  Are there other places
in the tree that could make use of the features in pnp/resource.c if
they were generally available?  I've had good luck in the past answering
questions ike this.

-- 
"Next the statesmen will invent cheap lies, putting the blame upon 
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain


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The SF.Net email is sponsored by EclipseCon 2004
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Re: ACPI and the PNP Layer

[Nate Lawson]

On Sun, 1 Feb 2004, Matthew Wilcox wrote:
> On Sun, Feb 01, 2004 at 02:41:02AM +0000, Dino Klein wrote:
> > I took a quick look at the two files, and they are quite comparable
> > code-wise; the additional size in 8250_pnp.c is due to the extra comments
> > and EISA IDs defined.
> > Now about the legacy devices - wouldn't you say that the keyboard/PS2
> > driver should be modified to register with the ACPI bus, just in order to
> > have everything nice & neat? or how about the parallel port, or motherboard
> > based IRDA (PNP0510)?
> > Perhaps I'm just exaggerating with this, but I like to have things nice and
> > neat :)
>
> PS/2 is obsoleted by USB, as is parallel.  I don't know abut IRDA but I
> would expect it to show up as a PCI device normally.  Are manufacturers
> still making machines which have this as a non-PCI device?  Remember just
> because it's on the motherboard doesn't mean it's a non-PCI device.

Compare the output of acpidump and the datasheet for a Super I/O chip some
time.  Everything on the LPCB is legacy and is thus probed through ACPI,
not PCI.  IRDA is almost always on the Super I/O.

http://www.via.com.tw/en/Products/superIO.jsp

-Nate


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