Adding new driver in Linux 2.6 - read fails with -1

[Ramkumar J]

On Jan 18, 2008 7:22 PM, Jenkins, Clive <Clive.Jenkins at xerox.com> wrote:

> > From: linuxppc-embedded-bounces+clive.jenkins=xerox.com at ozlabs.org
> > [mailto:linuxppc-embedded-bounces+clive.jenkins=xerox.com at ozlabs.org]
> > On Behalf Of Ramkumar J
> > Sent: 18 January 2008 10:54
> > To: linuxppc-embedded at ozlabs.org
> > Subject: Adding new driver in Linux 2.6 - read fails with -1
> >
> > Hi All,
> >
> > I m using the Linux 2.6(2.6.23-rc2) from Grants for ML-403 and
> > I tried to add a new driver for a hardware based stream.
> > [...] For read, the function doesnt seem calling the drivers read
> > routine and exits with -1. [...]
>
> You are not giving enough information -- better to supply the complete
> code of driver and application, and the complete kernel log, or put
> them on a web/ftp site and supply pointers to them.
>
> When your application calls read(), I cannot see whether you are
> passing a valid file descriptor, whether you have opened the device
> etc.  You say read() returns -1, but you don't give the value of errno
> or the error string corresponding to that value. An easy way to get
> this is to use perror() in your app.
>
> >         /* Wait while empty. */
> >         while (((status=readl( ((volatile unsigned char*)
> remapped_address)
> >  + 8)&3))==0)
>
> One thing I can see is that you have a "busy wait" loop in your
> driver's read method. This will waste CPU time and may hang
> indefinitely. Better to use wait-event_interruptible, and check for
> termination of the wait by unexpected events such as signals and
> changes of power management state.
>
> Clive
>



Hi,

Thanks a lot for replying. I will try using the perror() function and modify
the busy-loop through wait-for functions. Also, the way I have accessed the
memory mapped IO, is to ioremap() the physical address and then use readl()
functions. Is this correct.

Following is the link to the driver file,
http://www.geocities.com/ramkumarj_2000/impulse-stream.c
http://www.geocities.com/ramkumarj_2000/1.txt as impulse-stream.h
This is intermediate layer and part of my application space,
http://www.geocities.com/ramkumarj_2000/co_stream_linux.c

The application is,
http://www.geocities.com/ramkumarj_2000/HelloWorld.c
http://www.geocities.com/ramkumarj_2000/HelloWorld_sw.c

Logs at,
http://www.geocities.com/ramkumarj_2000/logs.txt
http://www.geocities.com/ramkumarj_2000/kernellog.txt

My apologies for the dirty code. To add some background, it starts from the
main() in HelloWorld.c and it proceeds calling the hear_hello() in
HelloWorld_sw.c . The co_stream_* functions are defined in intermediate
layer co_stream_linux.c and co_stream_open is defined to nothing in one
header file. The open and ioctl call ( modified a little in the driver now
for debugging) map from co_stream_attach.
co_stream_read is read and co_stream_write is the write to driver.

Though the logs indicate the call of release function before the read, I m
not quite sure about this as the read not being called have failed to get
inside the kernel messages.

Thanks and Regards,
Ramkumar.
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