Re: [Xenomai-help] rtdm_iomap_to_user question

[Jan Kiszka <jan.kiszka@domain.hid>]

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Zhang, Haobo wrote:
> Thanks, Jan. It is fixed after I modified my code as you suggested.

Good to hear. Now just please answer my question below related to
/dev/mem so that I can think about a generic solution for the
documentation or the code or rtdm_*map_to_user.

Jan

> 
> Best Regards,
> Haobo Zhang 
> 
> -----Original Message-----
> From: jan.kiszka@domain.hid [mailto:jan.kiszka@domain.hid
> Sent: May 11, 2007 12:22 PM
> To: Zhang, Haobo
> Cc: xenomai@xenomai.org; stelian@domain.hid
> Subject: Re: [Xenomai-help] rtdm_iomap_to_user question
> 
> Zhang, Haobo wrote:
>> Hi Jan,
>>
>> Thank you so much for your reply!
>>
>> In my driver, I wrote:
>>
>> int map_io( struct gpiodrv_context *dev_context, rtdm_user_info_t 
>> *user_info, struct MAPPED_IO *io ) {
>> 	int ret;
>>
>> 	if ((dev_context == 0) || (user_info == 0) || (io == 0))
>> 		return -EFAULT;
>>
>> 	if (dev_context->mapped_user_info != 0)
>> 	{
>> 		if ((ret = gpio_unmap_io( dev_context )) != 0)
>> 			return ret;
>> 	}
>>
>> 	dev_context->mapped_user_info = user_info;
>>
>> 	ret = rtdm_iomap_to_user( user_info, MPC52xx_PA( 
>> MPC52xx_GPIO_WKUP_OFFSET + 0x0C ),
>> 		1, PROT_READ | PROT_WRITE, (void
>> **)&(io->gpio_heart_beat), NULL, NULL );
> 
> Hmm, hmm. Looking at our code and the kernel again I would say we should
> catch non-page-aligned requests like this and document this pitfall
> better.
> 
> The mapping code always assumes page-alignment and rounds your physical
> address down. So what likely happened here is that you got a mapping,
> but with unexpected offset (gpio_heart_beat should point to MPC52xx_PA).
> 
>> 	
>> 	if (ret != 0)
>> 		goto __ERROR;
>> 	else
>> 		dev_context->mapped_heart_beat = (void
> *)io->gpio_heart_beat;
>> 	return 0;
>>
>> __ERROR:
>>
>> 	gpio_unmap_io( dev_context );
>> 	return ret;
>> }
>>
>> In the application, I wrote:
>>
>> int main(int argc, char *argv[])
>> {
>> 	int dev_gpio;
>> 	struct MAPPED_IO gpio;
>>
>> 	signal(SIGTERM, clean_exit);	
>> 	signal(SIGINT, clean_exit);	
>> 	
>> 	mlockall( MCL_CURRENT | MCL_FUTURE );
>>
>> 	rt_task_shadow( &mainapp, "mainapp", 1, 0 );
>>
>> 	dev_gpio = rt_dev_open( "gpio", 0 );
>> 	if (dev_gpio < 0)
>> 	{
>> 		return -1;
>> 	}
>> 	
>> 	gpio.gpio_heart_beat = NULL;
>>
>> 	if (rt_dev_ioctl( dev_gpio, 1, &gpio ) != 0)
>> 	{
>> 		return -1;
>> 	}
>>
>> 	gpio.gpio_heart_beat[0] = 0x01;
>>
>> 	...
>> }
>>
>> I also tried another way by opening "/dev/mem" and then using "mmap" 
>> to map the I/O memory addresses in the application. It worked!
>> I am very curious about why "rtdm_iomap_to_user" did not work for me. 
> 
> When you do precisely the same odd-numbered mapping via mmap on
> /dev/mem, you do get the right address at gpio_heart_beat (check if the
> start address ends with 0x0b0c)?
> 
> We either have to improve rtdm_iomap/mmap_to_user in this regard or
> catch unaligned requests. Probably it's easier to catch it so that the
> driver writer also realises that this is always about mapping full
> pages...
> 
> Jan
> 



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