udev rule for custom driver

udev rule for custom driver

[Justin Clacherty]

Hi,

I've been trying to get a udev rule to automatically create the /dev 
entries for the custom spi driver I've written for my board but am 
having no luck.  I've created the file /etc/udev/rules.d/10-spi.rules 
which contains the following line:

SUBSYSTEM="spi", SYSFS{modalias}="nexus_spi", NAME="nspi%n"

If I run udevmonitor and do a udev trigger I see the following line in 
the output:

UEVENT[1166449657.257561] add@/devices/platform/pxa2xx-spi.1/spi1.0

Running udevinfo on /devices/platform/pxa2xx-spi.1/spi1.0 gives:

  looking at device '/devices/platform/pxa2xx-spi.1/spi1.0':
    KERNEL="spi1.0"
    SUBSYSTEM="spi"
    SYSFS{modalias}="nexus_spi"

  looking at parent device '/devices/platform/pxa2xx-spi.1':
    ID="pxa2xx-spi.1"
    BUS="platform"
    DRIVER="pxa2xx-spi"
    SYSFS{modalias}="pxa2xx-spi"

  looking at parent device '/devices/platform':
    ID="platform"
    BUS=""
    DRIVER=""

Running udevtest on the sysfs tree gives the following output:

main: looking at device '/devices/platform/pxa2xx-spi.1/spi1.0' from 
subsystem 'spi'
main: run: 'socket:/org/kernel/udev/monitor'

Obviously I've missed something here, can anyone point to the problem?  
Do I need to add something to my driver for this to work or is my udev 
setup at fault?

Regards,
Justin.

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Re: udev rule for custom driver

[Alex Merry]

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On Tuesday 19 December 2006 00:41, Justin Clacherty wrote:
> Hi,
>
> I've been trying to get a udev rule to automatically create the /dev
> entries for the custom spi driver I've written for my board but am
> having no luck.  I've created the file /etc/udev/rules.d/10-spi.rules
> which contains the following line:
>
> SUBSYSTEM=="spi", SYSFS{modalias}=="nexus_spi", NAME="nspi%n"
[snip]
> Running udevinfo on /devices/platform/pxa2xx-spi.1/spi1.0 gives:
>
>   looking at device '/devices/platform/pxa2xx-spi.1/spi1.0':
>     KERNEL=="spi1.0"
>     SUBSYSTEM=="spi"
>     SYSFS{modalias}=="nexus_spi"

The original kernel name is spi1.0.  Do you get /dev/spi1.0 created 
already (ie: even without the rule)?  If not, I don't think your rule 
will help at all - udev doesn't think there's device to create, so 
simply renaming it to nspi won't do anything.  In the absence of a 
matching rule, udev will still create the device, but with the default 
name and some default permissions.

I don't know much about registering devices in the kernel, but there's 
some doc in the kernel, and no doubt Kay or Greg will be able to give 
your more helpful advice if this is the problem.  One other thing to 
check, though, is whether /sys/devices/platform/pxa2xx-spi.1/spi1.0/dev 
exists (it should have a major:minor pair to tell udev how to create 
the device).

Alex :-)


-- 
Pippin
Computer Monkey to the Pelican
www.oxrev.org.uk, www.corpusjcr.org, www.rev.org.uk
0870 120 0870, ext 26669

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Re: udev rule for custom driver

[Justin Clacherty]

Thanks Alex.

Alex Merry wrote:
> The original kernel name is spi1.0.  Do you get /dev/spi1.0 created already (ie: even without the rule)?

I thought it should automagically create /dev/spi1.0 but it doesn't.

> One other thing to check, though, is whether /sys/devices/platform/pxa2xx-spi.1/spi1.0/dev exists (it should have a major:minor pair to tell udev how to create the device).
>   

No, this doesn't exist, I guess that's the problem.  I can manually 
create the node and it works fine but if the major number changes (it's 
dynamic) then I'll have some problems - thus udev.  Looks like it's time 
to find out how to create the dev entry in /sys.  If anyone can help by 
pointing me to appropriate documents or code that'd be great.

Justin.

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Re: udev rule for custom driver

[Justin Clacherty]

Justin Clacherty wrote:
>
>
> No, this doesn't exist, I guess that's the problem.  I can manually 
> create the node and it works fine but if the major number changes (it's 
> dynamic) then I'll have some problems - thus udev.  Looks like it's time 
> to find out how to create the dev entry in /sys.  If anyone can help by 
> pointing me to appropriate documents or code that'd be great.
>   

It looks like all you need to do is create a new class in the module 
initialisation, then create new device classes for each device that is 
probed.  Once that is done the sys entries are created and udev is happy.

Justin.

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Re: udev rule for custom driver

[Kay Sievers]

On 12/19/06, Justin Clacherty <justin@redfish-group.com> wrote:
> Alex Merry wrote:
> > The original kernel name is spi1.0.  Do you get /dev/spi1.0 created already (ie: even without the rule)?
>
> I thought it should automagically create /dev/spi1.0 but it doesn't.
>
> > One other thing to check, though, is whether /sys/devices/platform/pxa2xx-spi.1/spi1.0/dev exists (it should have a major:minor pair to tell udev how to create the device).
> >
>
> No, this doesn't exist, I guess that's the problem.  I can manually
> create the node and it works fine but if the major number changes (it's
> dynamic) then I'll have some problems - thus udev.  Looks like it's time
> to find out how to create the dev entry in /sys.  If anyone can help by
> pointing me to appropriate documents or code that'd be great.

Set the dev_t value in "struct device" in your driver's devices,
otherwise udev doesn't know the major/minor and can't create any
device file. Doing this will automatically add the needed
MAJOR=/MINOR= to the event-environment and create the "dev" file in
sysfs.

Kay

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