Re: [PATCH] Longhaul - Disable arbiter

[Dave Jones <davej@redhat.com>]

On Tue, Aug 08, 2006 at 07:12:20PM +0200, Rafał Bilski wrote:
 > ACPI C3 works for "Powersaver" processors, so use it 
 > only for them.
 > 
 > Older CPU will change frequency on "halt" only. But we 
 > can protect transition in two ways:
 > - by ACPI PM2 register, there is "bus master arbiter 
 >   disable" bit. This isn't tested because VIA mainboards 
 >   don't have PM2 register,
 > - by PLE133 PCI/AGP arbiter disable register. There 
 >   are two bits in this register. First is "PCI arbiter 
 >   disable", second "AGP arbiter disable". This is 
 >   working on VIA Epia 800 mainboards.

The only part about this I don't like is that we now need to add
code to do similar things on every possible VIA chipset that
could take a C3, and there's quite a few of them, and until
we have good coverage...

 >  
 > +	/* Find ACPI data for processor */
 > +	acpi_walk_namespace(ACPI_TYPE_PROCESSOR, ACPI_ROOT_OBJECT, ACPI_UINT32_MAX,
 > +			    &longhaul_walk_callback, NULL, (void *)&pr);
 > +	if (pr == NULL) goto err_acpi;
 > +
 > +	if (longhaul_version == TYPE_POWERSAVER) {
 > +		/* Check ACPI support for C3 state */
 > +		cx = &pr->power.states[ACPI_STATE_C3];
 > +		if (cx->address == 0 || cx->latency > 1000) goto err_acpi;
 > +	} else {
 > +		/* Check ACPI support for bus master arbiter disable */
 > +		if (!pr->flags.bm_control) {
 > +			if ( !enable_arbiter_disable() ) {
 > +				printk(KERN_ERR PFX "No ACPI support. No VT8601 host bridge. Aborting.\n");
 > +		    		return -ENODEV;
 > +			} else
 > +				port22_en = 1;
 > +		}
 > +	}

We're going to -ENODEV, possibly breaking some setups that it might actually
already work on (even if only by chance).

		Dave

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