[2/5] char: tile-srom: Remove reference to platform_bus

Message ID 1407515691.31897.26.camel@hornet
State New
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Pawel Moll Aug. 8, 2014, 4:34 p.m.
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@arm.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@arm.com>
---
 drivers/char/tile-srom.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

Comments

Pawel Moll Aug. 8, 2014, 4:39 p.m. | #1
On Fri, 2014-08-08 at 17:34 +0100, Pawel Moll wrote:
> 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.  

(sorry, sent too early...)

By "device discovery" I meant the way you find the way in your devices
in /sysfs. You seem to be traversing /sys/devices/... tree, while you've
got almost direct access to them through /sys/class/srom and you can (I
believe, correct me if I'm wrong, Greg) rely on this path being stable.

Paweł

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Chris Metcalf Aug. 11, 2014, 2:38 a.m. | #2
Thanks for the code and comments. I'm out on vacation till mid next week but I'll look at this when I get back.
Chris

> On Aug 8, 2014, at 12:35 PM, "Pawel Moll" <pawel.moll@arm.com> wrote:
> 
> 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@arm.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@arm.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.
> 
> Paweł
> 
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Chris Metcalf Aug. 29, 2014, 6:43 p.m. | #3
(Resending with text/plain.)

First, sorry for the delayed response, with summer vacation and then
trying to catch up.  :-)

On 8/8/2014 12:34 PM, Pawel Moll wrote:
> 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?
>> By "device discovery" I meant the way you find the way in your devices
>> in /sysfs. You seem to be traversing /sys/devices/... tree, while you've
>> got almost direct access to them through /sys/class/srom and you can (I
>> believe, correct me if I'm wrong, Greg) rely on this path being stable.

Yes, this is an excellent point.  I will change the user tool to use
/sys/class instead and then it will work with the existing kernel as well
as with future kernels that incorporate your suggested change.

>> 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.
> [...]
> @@ -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);
>  }

The second argument should be &srom_parent.dev though, I think.  Right?

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

Yes, that seems slightly unfortunately but not too problematic.  If the
consensus is that this is the way to go, I can certainly take this change
into the Tile tree.
Pawel Moll Sept. 1, 2014, 12:27 p.m. | #4
On Fri, 2014-08-29 at 19:43 +0100, Chris Metcalf wrote:
> >> 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.
> > [...]
> > @@ -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);
> >  }
> 
> The second argument should be &srom_parent.dev though, I think.  Right?

Yes, sure - as I said, I haven't really tested this code, sorry!


> If the
> consensus is that this is the way to go, I can certainly take this change
> into the Tile tree.

That would be cool, and left us only with the scsi/DMA as the last user
of platform_bus. But this is a completely different story ;-)

Paweł

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Chris Metcalf Sept. 1, 2014, 1:53 p.m. | #5
On 9/1/2014 8:27 AM, Pawel Moll wrote:
> On Fri, 2014-08-29 at 19:43 +0100, Chris Metcalf wrote:
>> If the
>> consensus is that this is the way to go, I can certainly take this change
>> into the Tile tree.
> That would be cool, and left us only with the scsi/DMA as the last user
> of platform_bus. But this is a completely different story ;-)

OK, sounds good.  It's in the tile tree at linux-next now.

Patch hide | download patch | download mbox

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);
 }