linux-kernel - Re: [PATCH v4 00/13] Add ACPI _DSD and unified device properties support

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Date:	Wed, 14 Jan 2015 10:42:23 -0800
From:	David Woodhouse <dwmw2@...radead.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Darren Hart <dvhart@...ux.intel.com>
Subject: Re: [PATCH v4 00/13] Add ACPI _DSD and unified device properties
 support

I'm looking again at updating of_serial to work with ACPI properties. 

Specifically, I want to support a serial port with a non-standard baud
rate, something like this:

    Device(COM1) {
        Name(_HID, EisaId("PNP0501"))
        Name(_CID, EisaId("PRP0001"))
	Name(_DSD, Package() {
	    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
            Package () {
		Package () {"compatible", Package () {"ns16550a"}},
		Package () {"clock-frequency", 2457600},
	    }
	})
        ...
    }

Firstly, the of_serial driver doesn't even get *invoked* unless I do
this:

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index 0d08373..eb1201a 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2083,6 +2086,8 @@ static int acpi_add_single_object(struct acpi_device **child,
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Added %s [%s] parent %s\n",
 		dev_name(&device->dev), (char *) buffer.pointer,
 		device->parent ? dev_name(&device->parent->dev) : "(null)"));
+	if (device->data.of_compatible)
+		acpi_create_platform_device(device);
 	kfree(buffer.pointer);
 	*child = device;
 	return 0;

Now it doesn't work because it uses of_match_device() to look the device
up and find the corresponding *data* for that entry in its match table.
And without CONFIG_OF, I don't *have* of_match_device().

We've talked about the fact that the platform bus probe function doesn't
pass you the match ID. Is that something we could potentially fix now
that things are a little more unified?

Or do we expect drivers still to have to use something like
of_match_id() to do the lookup again for themselves... and in that case
should we make of_match_id() available or produce a new
device_match_id() that they are expected to switch to?

-- 
dwmw2

View attachment "of-serial-dev-properties.patch" of type "text/x-patch" (7650 bytes)

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