Date:	Sat, 27 Jan 2007 11:45:59 +0100
From:	Pieter Palmers <pieterp@...w.be>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
CC:	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [RFC] cycle timer read extension for raw1394/libraw1394

Stefan Richter wrote:
> (Cc lkml)
> 
> Pieter Palmers wrote to linux1394-devel:
>> Attached are two patches containing an extension to libraw1394 and the
>> kernel stack, implementing the simultaneous read of the isochronous
>> cycle timer and the system clock (in usecs). This implements what has
>> been requested before on the list.
>>
>> There is one issue left, namely that I didn't disable preemption when
>> doing the timer reads. In order to have a reliable simultaneous read of
>> both values, I think IRQ's and preemption should be disabled while
>> reading them.
> 
> Thus?
> 	preempt_disable();
> 	local_irq_save(flags);
> 
> 	read_cycle_timer;
> 	read_time_of_day;
> 
> 	local_irq_restore(flags);
> 	preempt_enable();
> 
> in hpsb_read_cycle_timer.
My main issue was that I still had to figure out how to do this... I'm a 
  very occasional kernel space programmer. Thanks for the hint, I'll do 
it like this.

I still have to check if I don't introduce a too long non-preemptible 
path though.

> 
>> Kernel patch applies against 2.6.20-rc6.
>> libraw1394 patch applies against SVN.
>>
>> Please comment.
>>
>> Greets,
>>
>> Pieter Palmers
>>
>>
>> ------------------------------------------------------------------------
>>
>> diff -u ../linux-2.6/drivers/ieee1394/ieee1394_core.c ieee1394-2.6.20/ieee1394_core.c
>> --- ../linux-2.6/drivers/ieee1394/ieee1394_core.c	2007-01-26 18:29:07.000000000 +0100
>> +++ ieee1394-2.6.20/ieee1394_core.c	2007-01-26 18:37:16.000000000 +0100
>> @@ -34,6 +34,8 @@
>>  #include <linux/suspend.h>
>>  #include <linux/kthread.h>
>>  
>> +#include <linux/time.h>
>> +
>>  #include <asm/byteorder.h>
>>  
>>  #include "ieee1394_types.h"
> 
> No empty line necessary above #include <linux/time.h>.
> 
>> @@ -940,6 +942,13 @@
>>  	}
>>  }
>>  
>> +void hpsb_read_cycle_timer(struct hpsb_host *host, u32 *ctr, u64 *local_time)
>> +{
>> +	struct timeval tv;
> 
> Empty line would be OK here.
> 
>> +	*ctr = host->driver->devctl(host, GET_CYCLE_COUNTER, 0);
>> +	do_gettimeofday(&tv);
>> +	*local_time=tv.tv_sec*1000000+tv.tv_usec;
>> +}
> 
> Couldn't this overflow?
> 	*local_time = tv.tv_sec * 1000000L + tv.tv_usec;
> or
> 	*local_time = tv.tv_sec * USEC_PER_SEC + tv.tv_usec;
Indeed. thx.

> 
>>  static void abort_requests(struct hpsb_host *host)
>>  {
>> @@ -1209,6 +1218,7 @@
>>  EXPORT_SYMBOL(hpsb_read);
>>  EXPORT_SYMBOL(hpsb_write);
>>  EXPORT_SYMBOL(hpsb_packet_success);
>> +EXPORT_SYMBOL(hpsb_read_cycle_timer);
>>  
>>  /** highlevel.c **/
>>  EXPORT_SYMBOL(hpsb_register_highlevel);
>> diff -u ../linux-2.6/drivers/ieee1394/ieee1394_core.h ieee1394-2.6.20/ieee1394_core.h
>> --- ../linux-2.6/drivers/ieee1394/ieee1394_core.h	2007-01-26 18:11:17.000000000 +0100
>> +++ ieee1394-2.6.20/ieee1394_core.h	2007-01-26 18:37:16.000000000 +0100
>> @@ -227,4 +227,8 @@
>>  extern struct class hpsb_host_class;
>>  extern struct class *hpsb_protocol_class;
>>  
>> +/* Reads the cycle timer, and the local time at which it was read.
>> + */
>> +void hpsb_read_cycle_timer(struct hpsb_host *host, u32 *ctr, u64 *local_time);
>> +
>>  #endif /* _IEEE1394_CORE_H */
> 
> (This reminds me that many of ieee1394's exported symbols lack kerneldoc
> comments.)
I'll change this one into proper kerneldoc format.

> 
> Alas I can't comment on the design & implementation of the userspace
> ABI, that's out of my league.
> 
>> diff -u ../linux-2.6/drivers/ieee1394/ieee1394-ioctl.h ieee1394-2.6.20/ieee1394-ioctl.h
>> --- ../linux-2.6/drivers/ieee1394/ieee1394-ioctl.h	2007-01-26 18:11:17.000000000 +0100
>> +++ ieee1394-2.6.20/ieee1394-ioctl.h	2007-01-26 18:40:04.000000000 +0100
>> @@ -100,5 +100,6 @@
>>  	_IO  ('#', 0x28)
>>  #define RAW1394_IOC_ISO_RECV_FLUSH		\
>>  	_IO  ('#', 0x29)
>> -
>> +#define RAW1394_IOC_GET_CYCLE_TIMER		\
>> +	_IOR ('#', 0x30, struct _raw1394_cycle_timer)
>>  #endif /* __IEEE1394_IOCTL_H */
>> diff -u ../linux-2.6/drivers/ieee1394/raw1394.c ieee1394-2.6.20/raw1394.c
>> --- ../linux-2.6/drivers/ieee1394/raw1394.c	2007-01-26 18:11:17.000000000 +0100
>> +++ ieee1394-2.6.20/raw1394.c	2007-01-26 18:37:16.000000000 +0100
>> @@ -2675,7 +2675,22 @@
>>  	return dma_region_mmap(&fi->iso_handle->data_buf, file, vma);
>>  }
>>  
>> -/* ioctl is only used for rawiso operations */
>> +/* read the Isochronous Cycle Counter along with the cpu time */
>> +static int raw1394_read_cycle_timer(struct file_info *fi, void __user * uaddr)
>> +{
>> +	struct _raw1394_cycle_timer ctr;
>> +	struct hpsb_host *host = fi->host;
>> +
>> +	hpsb_read_cycle_timer(host, &ctr.cycle_timer, &ctr.local_time);
>> +	if (copy_to_user(uaddr, &ctr, sizeof(ctr)))
>> +		return -EFAULT;
>> +
>> +	return 0;
>> +}
>> +
>> +/* ioctl is only used for rawiso operations,
>> + * and to read the cycle timer
>> + */
>>  static int raw1394_ioctl(struct inode *inode, struct file *file,
>>  			 unsigned int cmd, unsigned long arg)
>>  {
>> @@ -2772,6 +2787,13 @@
>>  		break;
>>  	}
>>  
>> +	switch(cmd) {
>> +		case RAW1394_IOC_GET_CYCLE_TIMER:
>> +			return raw1394_read_cycle_timer(fi, argp);
>> +		default:
>> +		break;
>> +	}
>> +
>>  	return -EINVAL;
>>  }
>>  
>> diff -u ../linux-2.6/drivers/ieee1394/raw1394.h ieee1394-2.6.20/raw1394.h
>> --- ../linux-2.6/drivers/ieee1394/raw1394.h	2007-01-26 13:15:58.000000000 +0100
>> +++ ieee1394-2.6.20/raw1394.h	2007-01-26 18:37:16.000000000 +0100
>> @@ -178,4 +178,11 @@
>>  	__s16 xmit_cycle;
>>  };
>>  
>> +/* Simultanous Isochronous Cycle Timer read and local clock read */
>> +struct _raw1394_cycle_timer {
>> +	__u32 cycle_timer;
>> +
>> +	/* local time in microseconds */
>> +	__u64 local_time;
>> +};
>>  #endif /* IEEE1394_RAW1394_H */
>>
>>
>> ------------------------------------------------------------------------
>>
>> Index: src/ieee1394-ioctl.h
>> ===================================================================
>> --- src/ieee1394-ioctl.h	(revision 168)
>> +++ src/ieee1394-ioctl.h	(working copy)
>> @@ -106,6 +106,6 @@
>>  	_IO  ('#', 0x28)
>>  #define RAW1394_IOC_ISO_RECV_FLUSH              \
>>  	_IO  ('#', 0x29)
>> -
>> -
>> +#define RAW1394_IOC_GET_CYCLE_TIMER		\
>> +	_IOR ('#', 0x30, struct _raw1394_cycle_timer)
>>  #endif /* __IEEE1394_IOCTL_H */
>> Index: src/raw1394.h
>> ===================================================================
>> --- src/raw1394.h	(revision 168)
>> +++ src/raw1394.h	(working copy)
>> @@ -118,7 +118,14 @@
>>  	RAW1394_MODIFY_FREE
>>  };
>>  
>> +/* Simultanous Isochronous Cycle Timer read and local clock read */
>> +struct raw1394_cycle_timer {
>> +	u_int32_t cycle_timer;
>>  
>> +	/* local time in microseconds */
>> +	u_int64_t local_time;
>> +};
>> +
>>  #ifdef __cplusplus
>>  extern "C" {
>>  #endif
>> @@ -328,6 +335,18 @@
>>   **/
>>  void raw1394_iso_shutdown(raw1394handle_t handle);
>>  
>> +/**
>> + * raw1394_get_cycle_timer - get the current value of the cycle timer
>> + * @handle: libraw1394 handle
>> + * @ctr: pointer to the target raw1394_cycle_timer struct
>> + *
>> + * Reads the cycle timer register, together with the system clock. It returns
>> + * a reasonable estimate of the system time the cycle timer was read.
>> + *
>> + * Returns: the error code of the ioctl, or 0 if successful.
>> + **/
> 
> The comment on accuracy could be dropped if preemption and IRQs are
> disabled, right?
> 
>> +int raw1394_read_cycle_timer(raw1394handle_t handle, struct raw1394_cycle_timer *ctr);
>> +
>>  typedef int raw1394_errcode_t;
>>  #define raw1394_make_errcode(ack, rcode) (((ack) << 16) | rcode)
>>  #define raw1394_internal_err(errcode) ((errcode) < 0)
>> Index: src/main.c
>> ===================================================================
>> --- src/main.c	(revision 168)
>> +++ src/main.c	(working copy)
>> @@ -478,3 +478,15 @@
>>          return 0;
>>  }
>>  
>> +int raw1394_read_cycle_timer(raw1394handle_t handle, struct raw1394_cycle_timer *ctr) 
>> +{
>> +	int err;
>> +
>> +	err = ioctl(handle->fd, RAW1394_IOC_GET_CYCLE_TIMER, ctr);
>> +	if(err != 0) {
>> +		return err;
>> +	}
>> +
>> +    return 0;
>> +}
>> +
>> Index: src/kernel-raw1394.h
>> ===================================================================
>> --- src/kernel-raw1394.h	(revision 168)
>> +++ src/kernel-raw1394.h	(working copy)
>> @@ -177,4 +177,11 @@
>>  	__s16 xmit_cycle;
>>  };
>>  
>> +/* Simultanous Isochronous Cycle Timer read and local clock read */
>> +struct _raw1394_cycle_timer {
>> +	__u32 cycle_timer;
>> +
>> +	/* local time in microseconds */
>> +	__u64 local_time;
>> +};
>>  #endif /* IEEE1394_RAW1394_H */
>>
>>
> 

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