Re: [ACPI] [PATCH/RFC 0/4]Bind physical devices with ACPI devices

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Nov 08, 2004 at 12:11:06PM +0800, Li Shaohua wrote:
> ACPI provides many functionalities for physical devices. Such as for
> suspend/resume, ACPI can tell us correct devices D-state for S3. There
> are tons of devices enhancement for both realtime and boot time from
> ACPI. To utilize ACPI, physical devices like PCI devices must know its
> partner. The patches try to do this. After this is done, we can enhance
> many features, such as improve suspend/resume.
> These patches are against 2.6.10-rc1, please give your comments.

I don't think this is a great way to do it.  There's at least two other
examples of firmware that interacts with drivers in a similar way that you
could look at -- PA-RISC's PDC and Sun/Apple/IBM OpenFirmware.  I don't
know much about OpenFirmware, and I just redid the way parisc_device
works, so I'll discourse about that for a bit.

>From a driver's point of view, it's simple.  Call a function to get
a cookie (an acpi_handle for ACPI, I guess), then pass that cookie to
whatever functions necessary.  This is the code in the sym2 SCSI driver:

#ifdef CONFIG_PARISC
/*
 * Host firmware (PDC) keeps a table for altering SCSI capabilities.
 * Many newer machines export one channel of 53c896 chip as SE, 50-pin HD.
 * Also used for Multi-initiator SCSI clusters to set the SCSI Initiator ID.
 */
static int sym_read_parisc_pdc(struct sym_device *np, struct pdc_initiator *pdc)
{
        struct hardware_path hwpath;
        get_pci_node_path(np->pdev, &hwpath);
        if (!pdc_get_initiator(&hwpath, pdc))
                return 0;

        return SYM_PARISC_PDC;
}
#else
static int sym_read_parisc_pdc(struct sym_device *np, struct pdc_initiator *x)
{
        return 0;
}
#endif


Hm.. ACPI doesn't really hanve anything SCSI-related in it.  Let's look at
IDE's _GTM and _STM for examples.  

static void ide_acpi_gtm(struct hwif_s *hwif, struct acpi_timing_mode *tm)
{
	acpi_handle handle;
	acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL};
	acpi_status status;

	handle = acpi_get_gendev_handle(&hwif->gendev);
	status = acpi_evaluate_object(handle, "_GTM", NULL, &buffer);
	...
}

All we need is an acpi_get_gendev_handle that takes a struct device and
returns the acpi_handle for it.  Now, maybe that'd be best done by placing
a pointer in the struct device, but I bet it'd be just as good to walk
the namespace looking for the corresponding device.

-- 
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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