- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: IEEE-754 Float to int
by Lucas Tanure Nov. 22, 2016

Nov. 22, 2016

On Tue, Nov 22, 2016 at 4:39 PM, Greg KH <greg(a)kroah.com> wrote: > On Tue, Nov 22, 2016 at 04:05:18PM +0000, Lucas Tanure wrote: > > Hi, > > > > At some point my hardware gives me a 32bit IEEE-754 float, like this : > > > > > > regmap_read(device->regmap, ADDR0, &temp); > > > > value = temp << 16; > > > > regmap_read(device->regmap, ADDR1, &temp); > > > > value |= temp; > > > > > > So, value has a 32bit float now, and I would like to print just the > integer > > part, like : > > Read 26.92387 --> Print 26. > > Simple, no float operations. > > > > How I can do it ? > > Just print the upper 16 bits shifted right by 16 bits. > But why would you want to print the value anyway? Who would use it? > My hardware gives me the board temperature as a float 32bits. And the hwmon sysfs api asks me to return the temperature as millidegree Celsius. To follow the hwmon sysfs api rules <https://www.kernel.org/doc/Documentation/thermal/sysfs-api.txt>, I need to get my float, multiply by 1000 and print the integer part. There is a better way to do that ? > thanks, > > greg k-h > Thanks -- Lucas Tanure

1 0

IEEE-754 Float to int
by Lucas Tanure Nov. 22, 2016

Nov. 22, 2016

Hi, At some point my hardware gives me a 32bit IEEE-754 float, like this : regmap_read(device->regmap, ADDR0, &temp); value = temp << 16; regmap_read(device->regmap, ADDR1, &temp); value |= temp; So, value has a 32bit float now, and I would like to print just the integer part, like : Read 26.92387 --> Print 26. Simple, no float operations. How I can do it ? Thank! -- Tanure

3 5

Non-zero preemption count on voluntary preemptive kernel
by Alexander Lochmann Nov. 22, 2016

Nov. 22, 2016

Hi folks! I'm sorry to bother you, guys, but neither the mailing list 'kpreempt-tech(a)lists.sourceforge.net' nor Robert's address 'rml(a)tech9.net' exist anymore. If I have to address someone else, pls let me know. We're currently investigating the locking of data structures in the Linux Kernel -- namely 3.16. Doing so, we've been logging every call to *lock() or *unlock(). For further analysis, we log the preempt count as well. Although we use a voluntary preemptive kernel (defined(CONFIG_PREEMPT_VOLUNTARY) && !defined(CONFIG_PREEMPT) && !defined(CONFIG_PREEMPT_COUNT), the actual preemption count, the first eight bits, aren't zero all time. I'd expect the kernel to not touch those bits, because the preempt_{enable,disable} functions do nearly nothing in my case. They actually insert a memory barrier, but nothing more. As you can see in the file (query.txt) attached to this mail, there are several occasions where the preemption count is above zero. I'm a bit puzzled why this happens... The format is as follows: The first three columns donate the position within the source code where a lock has been acquired. The fourth column is the preemption count, as returned by preemption_count(), after acquiring the lock. The last column tells how often this happens. I attached my kernel config as well. Can you please tell why this happens? Have I missed something? Might this be a bug? Thanks! Regards, Alex -- Technische Universität Dortmund Alexander Lochmann PGP key: 0xBC3EF6FD Otto-Hahn-Str. 16 phone: +49.231.7556141 D-44227 Dortmund fax: +49.231.7556116 http://ess.cs.tu-dortmund.de/Staff/al

1 0

patch against linux-next
by Amit Kumar Nov. 22, 2016

Nov. 22, 2016

Hi, As far as I know that linux-next tree is a preview of patches which will be merged in the mainline kernel. I've noticed that recently linux-next is updated with a gap. Can a patch be created against linux-next tree? A kernel newbie, Amit Kumar

3 7

Append Localversion to Kernel String
by Marco Gross Nov. 20, 2016

Nov. 20, 2016

Hello folks, I'm trying to automatically append version information to my kernel's version string. Therefore, I have in my .config following option: CONFIG_LOCALVERSION_AUTO=y Additionally, following is set: CONFIG_LOCALVERSION="++" The output that is expected is said to be the first eight characters of the output of 'git rev-parse --verify HEAD'. The output in my kernel directory is: $ git rev-parse --verify HEAD c8d2bc9bc39ebea8437fd974fdbc21847bb897a3 After installing the kernel the name of the kernel is as follows: vmlinuz-4.8.0++ I expected: vmlinuz-4.8.0++-gc8d2bc9b My question: Where is the version string that I expected? Marco Mit freundlichen Gr??en / Best regards Marco Gross Diplomand [cid:LogoFritzStephan72dpi120x55Pixel_cfdd7a92-cbea-435d-a419-8d088e6ed7a8.png] Fritz Stephan GmbH - Medizintechnik - Kirchstra?e 19, D-56412 Gackenbach Tel.: +49 6439 9125-249 Fax: +49 6439 9125-111 E-Mail: mgross(a)stephan-gmbh.com<mailto:mgross@stephan-gmbh.com> Web: www.stephan-gmbh.com Handelsregister Amtsgericht Montabaur HR-Nr. 4241 Gesch?ftsf?hrer: Tanja Stephan, Georg Mainusch [cid:Eve_Signatur_145525f8-5839-48a6-8419-4e43941739b5.jpg] [cid:YouTube-logo-full_color_362f623d-4265-4133-9721-da6b905f4c25.png] <https://www.youtube.com/channel/UCtILKk6D8klJo5FwlycY82w>

3 2

Review on spi driver
by Arthur LAMBERT Nov. 19, 2016

Nov. 19, 2016

Hi, Not sure that it is the good place to do that. I am quite new in kernel dev and it will be great to have some review/advise on a implementation in kernel. My need : Read periodically data from a sensor with spi. I know that data is available thanks to a GPIO. Data are available every 2 ms. First step for me was to : Declare a irq handler on the ready signal GPIO thanks to gpio_to_irq and request_irq function. First I try to read from spi in my irq handler.I finally understand that I cannot make call which implies sleep in irq handler like spi_sync for example. I finally use wake_up_interruptible call in my irq handler to make the spi work in another piece of code. static irqreturn_t irq_handler(int irq, void *id) { flag = 1; wake_up_interruptible(&wq); return IRQ_HANDLED; } On my first try I just use a kernel thread which read data from spi and then which send my data to userspace thanks to a netlink socket. while(!kthread_should_stop()) { wait_event_interruptible(wq, flag != 0 || kthread_should_stop()); if (kthread_should_stop()) do_exit (0); flag = 0; // read data from spi (...) // send data in netlink socket skb = nlmsg_new(NLMSG_ALIGN(msg_size + 1), GFP_ATOMIC); nlh = nlmsg_put(skb, 0, 1, NLMSG_DONE, msg_size + 1, 0); memcpy(nlmsg_data(nlh), spi->rx_buf, msg_size); ret = nlmsg_multicast(nl_sk, skb, 0, MYGRP, GFP_ATOMIC); schedule(); // not sure that I need this line of code. } Problem I was not sure that netlink socket was the best solution to my problem. Also I was not able to use the same socket during my data acquisition. I must call nlmsg_new on each new data sample. Other strange stuff, If I call nsmsg_free at the end of the process I have big stability issue during my test. Moreover, if I am to slow to send data from kernel space to user space, I will miss event from my irq handler and miss sample from my sensor. My second try was to use a character device to send data from kernel space to userpsace. I was already using the character device to drive my kernel driver. Open/Release to init/clean sensor. And ioctl to send command to the sensor like start/stop acquisition. So my plan was just to add a read callback on the character device. static const struct file_operations fops = { .owner = THIS_MODULE, .unlocked_ioctl = ads_ioctl, .open = ads_open, .release = ads_release, .read = ads_read, .unlocked_ioctl = ads_ioctl, }; static int ads_read(struct file *filp, char __user *data, size_t len, loff_t *ppos) { struct ads_dev *dev = filp->private_data; wait_event_interruptible(wq, flag != 0); flag = 0; // read data from spi (...) copy_to_user(data, spi->rx_buf, DATA_SIZE); return DATA_SIZE; }; This code seems to be easy compare to the netlink solution. Even in the user space code side. Just need to use a read instead of using socket and libnl. But the problem is always there. If the read operation over the spi and the copy_to_user take more than 2 ms, I will lost sample from my sensor. My last plan was to use mixed the two previous solutions and use a kthread + the character device. The irq wake up the thread. I read data over spi. I put the data in a queue. The read callback from character device will gather data from the queue. I have always a synchrone call which can take more than 2 ms. But At least I can send the data to user space in a synchrone way. But I was not able to find a proper way to use a queue with semaphore. So it was quite basic. A static queue + offset + wake_up_interruptible/wait_event_interruptible to synchronize kernel thread and my read callback. static uint8_t queue[50 * DATA_SIZE]; static int read_offset = 0; static int write_offset = 0; I guess that my problems are quite common in kernel driver which want to gather some data over spi. Is there a good kernel driver that I can take as good practice/example to implement my solution ? Feel free to say that my code is stupid ! Thanks, Arthur.

2 1

Which header file?
by Amit Kumar Nov. 17, 2016

Nov. 17, 2016

Hi, In linux/include/linux/atomic.h, there are two files included asm/atomic.h and asm/barrier.h. Both files are present in linux/include/asm-generic and linux/arch/arm/include/asm. If I build like, CROSS_COMPILE=arm-linux-gnueabi- ARCH=arm make zImage dtbs then which file is being used. A kernel newbie, Amit Kumar

2 2

TCP as a module
by Md. Islam Nov. 15, 2016

Nov. 15, 2016

Hi Currently TCP is statically linked to the kernel. How can I make it a loadable module? I need to modify TCP (tcp_input.c and tcp_output.c). It would be easier for my development if it's just another module (I don't need to restart every time). I changed the *fs_initcall(inet_init)* to *module_init(inet_init)*, but doesn't seem to help. Looking forward to your suggestions. Many thanks Tamim

3 4

Catching invoking a new process by the audit subsyetm
by Kevin Wilson Nov. 14, 2016

Nov. 14, 2016

Hi, Is it possible to catch invoking a new process by the audit subsyetm? Regards, Kevin

1 0

How to get involved with the latest kernel development?
by Hao Lee Nov. 10, 2016

Nov. 10, 2016

Hi, everyone I'm very interested in memory management, so I have read many materials such as Understanding the Linux Virtual Memory Manager and Understanding the Linux Kernel (2nd). These books are all about kernel 2.4 and I have read the source code of kernel 2.4 for a long time. I once thought I can use kernel 2.4 as my stepping-stone and begin my journey of kernel development, but I feel frustrated. Kernel 2.4 and kernel 4.4.30 are almost completely different! I can't even find a familiar function and I don't know how to begin. I want to contribute to mm subsystem and I believe many developers in this list are more experienced than me, so could you give me some advice. Thanks! Regards, Hao Lee

2 1