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Date:	Mon, 10 Mar 2014 10:44:28 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	bhelgaas@...gle.com, matthew.garrett@...ula.com,
	rafael.j.wysocki@...el.com, dmitry.torokhov@...il.com
Subject: Re: [RFC PATCH 6/8] ACPI: use platform bus as the default bus for
 _HID enumeration

On Sun, 2014-03-09 at 19:04 +0100, Rafael J. Wysocki wrote:
> On Sunday, March 09, 2014 11:50:37 PM Zhang Rui wrote:
> > On Wed, 2014-02-26 at 17:11 +0800, Zhang Rui wrote:
> > > Because of the growing demand for enumerating ACPI devices to platform bus,
> > > this patch changes the code to enumerate ACPI devices with _HID/_CID to
> > > platform bus by default, unless the device already has a scan handler attached.
> > > 
> > > Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> > > ---
> > >  drivers/acpi/acpi_platform.c |   28 ----------------------------
> > >  drivers/acpi/scan.c          |   12 ++++++------
> > >  2 files changed, 6 insertions(+), 34 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
> > > index dbfe49e..33376a9 100644
> > > --- a/drivers/acpi/acpi_platform.c
> > > +++ b/drivers/acpi/acpi_platform.c
> > > @@ -22,24 +22,6 @@
> > >  
> > >  ACPI_MODULE_NAME("platform");
> > >  
> > > -/*
> > > - * The following ACPI IDs are known to be suitable for representing as
> > > - * platform devices.
> > > - */
> > > -static const struct acpi_device_id acpi_platform_device_ids[] = {
> > > -
> > > -	{ "PNP0D40" },
> > > -	{ "ACPI0003" },
> > > -	{ "VPC2004" },
> > > -	{ "BCM4752" },
> > > -
> > > -	/* Intel Smart Sound Technology */
> > > -	{ "INT33C8" },
> > > -	{ "80860F28" },
> > > -
> > > -	{ }
> > > -};
> > > -
> > >  /**
> > >   * acpi_create_platform_device - Create platform device for ACPI device node
> > >   * @adev: ACPI device node to create a platform device for.
> > > @@ -125,13 +107,3 @@ int acpi_create_platform_device(struct acpi_device *adev,
> > >  	kfree(resources);
> > >  	return 1;
> > >  }
> > > -
> > > -static struct acpi_scan_handler platform_handler = {
> > > -	.ids = acpi_platform_device_ids,
> > > -	.attach = acpi_create_platform_device,
> > > -};
> > > -
> > > -void __init acpi_platform_init(void)
> > > -{
> > > -	acpi_scan_add_handler(&platform_handler);
> > > -}
> > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > > index 5967338..61af32e 100644
> > > --- a/drivers/acpi/scan.c
> > > +++ b/drivers/acpi/scan.c
> > > @@ -2022,14 +2022,15 @@ static int acpi_scan_attach_handler(struct acpi_device *device)
> > >  		handler = acpi_scan_match_handler(hwid->id, &devid);
> > >  		if (handler) {
> > >  			ret = handler->attach(device, devid);
> > > -			if (ret > 0) {
> > > +			if (ret > 0)
> > >  				device->handler = handler;
> > > -				break;
> > > -			} else if (ret < 0) {
> > > -				break;
> > > -			}
> > > +			if (ret)
> > > +				goto end;
> > >  		}
> > >  	}
> > > +end:
> > > +	if (!list_empty(&device->pnp.ids) && !device->handler)
> > > +		acpi_create_platform_device(device, NULL);
> > 
> > I just found a big problem in this proposal, which affects all the
> > optional scan handlers.
> 
> What do you mean by "optional"?  Such that can be compiled out?
> 
yes.

> > The problem is that, if we disable a scan handler, platform device nodes
> > would be created instead by the code above, because there is no scan
> > handler attached for those ACPI nodes.
> 
> If "we disable a scan handled" means "we compile it out", I'm not sure
> why creating platform devices for the device objects in question will
> be incorrect?
> 
take lpss scan handler and 80860F0A device for example,
acpi_lpss_create_device() would invoke lpss_uart_setup() first and then
register 80860F0A as a platform device.
if the lpss scan handler is compiled out, we would do nothing but
register a platform device directly, thus the dw8250_platform_driver
driver is still loaded, but probably breaks.

IMO, we should either have a full functional platform device (if the
scan handler is compiled in) or nothing (if the scan handler is compiled
out).

thanks,
rui
> Rafael
> 
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