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Kernel support for video and graphics overlay
by Thomas Petazzoni Aug. 4, 2011

Aug. 4, 2011

Hello, I am starting to work on a SuperH processor that has a graphics controller capable of overlaying three layers : * one video layer, where the video comes from a camera interface * two graphics layer A single hardware, controlled by a single set of registers, manages the whole graphics controller. At the moment, the kernel only has a framebuffer driver capable of outputting things on one graphic layer. I'd like to be able to use the video layer, in order to inlay the video coming from the camera into a graphical application. My understanding is that the Video 4 Linux subsystem will play a role in managing both the video input and the video output devices. However, I can't seem to figure out how the work is divided between the video input driver, the video output driver and the framebuffer driver. Do you have pointers, or example of drivers for similar devices ? Thanks, Thomas -- Thomas Petazzoni, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com

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SYSLOG_ACTION_READ_ALL question
by William Douglas Aug. 4, 2011

Aug. 4, 2011

Hello all, I'm trying to figure out why the do_syslog code in kernel/printk.c is using put_user instead of copy_to_user. There is even a comment about how because of sleep, the buffer is read from back to front to minimize the impact of printk overwriting the syslog section we are using. That wouldn't be necessary if a temporary copy was made and then written out with copy_to_user. Does that make sense or am I missing something? Thanks, William

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SRIO maintenance read hangs (mpc8548)
by shrikant hegde Aug. 4, 2011

Aug. 4, 2011

Hi all, I am working on srio; When i tried to send maintenance packet to switch it hangs. Symptom when i tried to read DIDCAR of switch,( i.e read 0x8000_0000 ), or HDIDLOCK (0x8000_0068 ), execution of code hangs; if i press break in code warrior its coming out with an error. register value dump EPWISR 0x80000000 -- physical or logical/transport error interrupt LTLEDCSR 0x08000000 -- illegal transaction decode, received request/response packet LTLCCCSR 0x82000000 Below are my system detail: Processor mpc8548 and Tsi578 switch. Processor is connected to switch on same board.I have written standalone code (no OS) to exercise srio, using code warrior. Processor side configurations Its configured to 1x, 2.5gbs, host. law and tlb are configured. 0x8000_0000 0x8FFF_FFFF maintenance window configured 0x8000_0000 0x8000_0FFF (4k) switch side configuration 1x,2.5gbs, swap disabled (configured during POR) Processor side link training bit is setting. Am I missing any configuration , in switch side or processor side ? Any pointer is very helpful. Forgive me if its a wrong forum to post srio queries. thanks shrikant -- View this message in context: http://old.nabble.com/SRIO-maintenance-read-hangs-%28mpc8548%29-tp30949266p… Sent from the kernelnewbies mailing list archive at Nabble.com.

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Usage of unlikely in RCU code
by Julie Sullivan Aug. 3, 2011

Aug. 3, 2011

Hi list, I'm looking at RCU at the moment and (on reading a recent article by Paul McKenney on LWN) I've spotted something I'm a bit confused by in this code, a function which is defined in kernel/rcutree_plugin.h: void __rcu_read_unlock(void) { struct task_struct *t = current; barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ --t->rcu_read_lock_nesting; barrier(); /* decrement before load of ->rcu_read_unlock_special */ if (t->rcu_read_lock_nesting == 0 && unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) rcu_read_unlock_special(t); #ifdef CONFIG_PROVE_LOCKING WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); #endif /* #ifdef CONFIG_PROVE_LOCKING */ } Specifically, the conditional if (t->rcu_read_lock_nesting == 0 && unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) rcu_read_unlock_special(t); I've googled for 'likely/unlikely' and i've seen if (unlikely(... before in kernel code, and I might understand if the logical operator here were || not &&, but why is the 'unlikely' attribute only applied to the second operand here? Because both must be evaluated, with left-to-right associativity, and then both must be true for the branch to be taken, right? If it's necessary for branch prediction/optimization purposes shouldn't it be applied to both or the first one? Or might the operands also be re-ordered by the compiler or processor so that the second is evaluated before the first? What am I misunderstanding about this attribute? Cheers Julie

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Re: Usage of unlikely in RCU code
by Julie Sullivan Aug. 3, 2011

Aug. 3, 2011

Thanks, Adam, your input has helped to clarify my thinking and is reassuring - I was beginning to confuse myself quite a lot! I must try not to do so much of the brain thing late at night, it rarely works out well... ;-) Cheers Julie

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[net] Hacking the wholism of GNU/Linux net*
by Shawn Aug. 3, 2011

Aug. 3, 2011

hi guys, I have written an article[1] for newbies who are willing to learn networking stuff in linux kernel. I hope this introduction-level article can help you understand the mechanism of netfilter and NIC driver. For this article, any critical comments are welcomed! [1] http://hfg-resources.googlecode.com/files/hacking_the_wholism_of_linux_net.… -- GNU powered it... GPL protect it... God blessing it... regards Shawn -- GNU powered it... GPL protect it... God blessing it... regards Shawn

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understanding the SCSI Specification.
by RKK Aug. 3, 2011

Aug. 3, 2011

HI all, Im working on a storage protocol which uses SCSI commands set as the command set and also the SCSI Task Management functions for processing the Task Management. The Architectural Model is based on SAM-5. The Command set is based on SPC-4 and SBC-3. I have some doubts in trying to understanding some SCSI terms and definitions. For using the send command transport protocol service request to request a initiator the following API is defined [1]Send SCSI Command (IN (I_T_L_Q Nexus, CDB, Task Attribute, [Data-in Buffer Size], [Data- out Buffer], [Data-out Buffer Size], [CRN], [Command Priority], [First Burst Enabled])) Here I want to know what relation does the I_T_L_Q tries to convey. from what it says in SAM-5 Specification section 4.8 tries to define the Nexus as " nexus represents a relationship between a SCSI initiator port, a SCSI target port, optionally a logical unit, and optionally a command." how do we convey this information in the above [1]. Also can someone help me in how to map the initiator-target relation to host-device structure? thanks. Warm Regards, Ravi Kulkarni. Warm Regards, Ravi Kulkarni.

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can LTP be used to verify the ASIC design of peripherals
by Gang Lei (雷刚) Aug. 2, 2011

Aug. 2, 2011

HI : Is it appropriate to use linux test project for ASIC verification purpose?such as msdc controller? Has someone already done it with LTP? Thanks for your help. Regards Rui

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Tasklet vs workqueues
by santhosh kumars Aug. 2, 2011

Aug. 2, 2011

Hi All, I took following lines from robert love linux kernel development. " If you need a schedulable entity to perform your bottom-half processing, you need work queues.They are the only bottom-half mechanisms that run in process context, and thus, the only ones that can sleep.This means they are useful for situations in which you need to allocate a lot of memory, obtain a semaphore, or perform block I/O. If you do not need a kernel thread to handle your deferred work, consider a tasklet instead ." Here some times tasklets also runs in kernel thread context(by ksoftirqd/n).So I want to know what is the exact difference between workqueue and tasklet. thanks, santosh.

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How to isolate Hardware for one particular process
by bill Aug. 2, 2011

Aug. 2, 2011

Hi, God I'm doing some experiment on Linux to isolate an hardware for one particular process to use, and at the same time preventing other process to use it. As far as my understanding, cgroup could archive cpu/mem/sched control at process unit, then how to provide such control on some other hardware like serial port/nic ? Is there any mechanism in linux enables me to do so? thanks bill

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