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Date:	Fri, 08 Aug 2014 17:34:51 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Olof Johansson <olof@...om.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"paul@...an.com" <paul@...an.com>, Arnd Bergmann <arnd@...db.de>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"arm@...nel.org" <arm@...nel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] char: tile-srom: Remove reference to platform_bus

On Tue, 2014-08-05 at 21:08 +0100, Chris Metcalf wrote:
> >> In addition, we also have user binaries
> >> in the wild that know to look for /sys/devices/platform/srom/ paths,
> >> so I'm pretty reluctant to change this path without good reason.
> > So what is the srom class for then if not for device discovery? And why
> > do they look for them in the first place? To get relevant character
> > device's data, if I understand it right?
> >
> > Maybe you could just register a simple "proper" platform device for all
> > the sroms and then hang the class devices from it? I can type some code
> > doing this if it sound reasonably?
> 
> I'm not sure exactly what you mean by device discovery here.  



> The
> subdirectories under /sys/devices/platform/srom/ correspond to partitions
> in the SPI-ROM, which are software constructs created by the Tilera hypervisor.
> By default we have three, where the first holds boot data that the chip
> can use to boot out of hardware, and the other two are smaller partitions
> for boot- and user-specific data.  We use the /sys files primarily to get the
> page size and sector size for the sroms, and also export other interesting
> information like the total size of the particular srom device.
> 
> Thank you for volunteering to write a bit of code; if that's the best
> way to clarify this for us, fantastic, or else pointing us at existing
> good practices or documentation would be great too.

I was thinking about something like the following (warning, untested)

8<-------------------------------------------
>From c53f0a2492d6cd38d1f82d57916a6528b071e8a8 Mon Sep 17 00:00:00 2001
From: Pawel Moll <pawel.moll@....com>
Date: Fri, 8 Aug 2014 16:32:58 +0100
Subject: [PATCH] char: tile-srom: Add real platform bus parent

Add a real platform bus device as a parent for
the srom class devices, to prevent non-platform
devices hanging from the bus root.

Signed-off-by: Pawel Moll <pawel.moll@....com>
---
 drivers/char/tile-srom.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tile-srom.c b/drivers/char/tile-srom.c
index bd37747..7fb0fd5 100644
--- a/drivers/char/tile-srom.c
+++ b/drivers/char/tile-srom.c
@@ -76,6 +76,7 @@ MODULE_LICENSE("GPL");
 
 static int srom_devs;			/* Number of SROM partitions */
 static struct cdev srom_cdev;
+static struct platform_device *srom_parent;
 static struct class *srom_class;
 static struct srom_dev *srom_devices;
 
@@ -350,7 +351,7 @@ static int srom_setup_minor(struct srom_dev *srom, int index)
 		       SROM_PAGE_SIZE_OFF, sizeof(srom->page_size)) < 0)
 		return -EIO;
 
-	dev = device_create(srom_class, &platform_bus,
+	dev = device_create(srom_class, srom_parent,
 			    MKDEV(srom_major, index), srom, "%d", index);
 	return PTR_ERR_OR_ZERO(dev);
 }
@@ -415,6 +416,13 @@ static int srom_init(void)
 	if (result < 0)
 		goto fail_chrdev;
 
+	/* Create a parent device */
+	srom_parent = platform_device_register_simple("srom", -1, NULL, 0);
+	if (IS_ERR(srom_parent)) {
+		result = PTR_ERR(srom_parent);
+		goto fail_pdev;
+	}
+
 	/* Create a sysfs class. */
 	srom_class = class_create(THIS_MODULE, "srom");
 	if (IS_ERR(srom_class)) {
@@ -438,6 +446,8 @@ fail_class:
 		device_destroy(srom_class, MKDEV(srom_major, i));
 	class_destroy(srom_class);
 fail_cdev:
+	platform_device_unregister(srom_parent);
+fail_pdev:
 	cdev_del(&srom_cdev);
 fail_chrdev:
 	unregister_chrdev_region(dev, srom_devs);
@@ -454,6 +464,7 @@ static void srom_cleanup(void)
 		device_destroy(srom_class, MKDEV(srom_major, i));
 	class_destroy(srom_class);
 	cdev_del(&srom_cdev);
+	platform_device_unregister(srom_parent);
 	unregister_chrdev_region(MKDEV(srom_major, 0), srom_devs);
 	kfree(srom_devices);
 }
-- 
1.9.1
8<-------------------------------------------

Would that work for you? Note that it will move the srom class devices
one level deeper in /sys/devices/... hierarchy.

PaweĊ‚

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