December 2015 - kernelnewbies@kernelnewbies.org

Ftrace: tracing init call of out of tree modules
by Jay Aurabind Dec. 11, 2015

Dec. 11, 2015

Hi, I am learning ftrace. I would like to know to use frace filters for tracing a module's init function. For example, assume the module uvcvideo. While the module is loaded, cat available_filter_functions | grep uvcvideo will give me a big list of functions. Then I enable those functions by setting ftrace filter with: echo "uvc*" > set_ftrace_filter However, as soon as I rmmod the driver, set_ftrace_filter becomes empty automatically. So how do I do a trace on out-of-tree modules I have ? -- Thanks and Regards, Aurabindo J

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Fwd: objdiff
by sasa bogicevic Dec. 10, 2015

Dec. 10, 2015

> Hi All, > I am trying to prove that my changes in code in complete drivers/pci/hotplug folder didn’t brake anything so I: > get the staging-testing tree > compile just drivers/pci/hotplug folder > use ./scripts/objdiff record drivers/pci/hotplug > make changes > commit > compile again just that folder > record again with objdiff > and when I do ./scripts/objdiff diff commit1 commit2 I get no output. > Is this normal? How do I prove all compiles normally ? { name: Bogicevic Sasa phone: +381606006200 }

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What is the return value of test_bit() in <asm/bitops.h> on x86_64?
by Le Tan Dec. 10, 2015

Dec. 10, 2015

Hi, I was shocked when I found that `test_bit()` will return -1 or 0 to denote whether a bit is set or not in a bitmap. Looking at its implementation here: ``` static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr) { return ((1UL << (nr & (BITS_PER_LONG-1))) & (addr[nr >> _BITOPS_LONG_SHIFT])) != 0; } static inline int variable_test_bit(long nr, volatile const unsigned long *addr) { int oldbit; asm volatile("bt %2,%1\n\t" "sbb %0,%0" : "=r" (oldbit) : "m" (*(unsigned long *)addr), "Ir" (nr)); return oldbit; } ``` The sbb instruction will let `det = dst - (src + CF)`. So it seems that test_bit() will return -1 if a bit is set? And it seems to work that way in my project. However, when I wrote another toy function to test it, I saw that it will return 1 for those bits set. ``` #define TEST_MAX_BITS 512 static void rr_unit_test(struct kvm_vcpu *vcpu) { static u64 counter = 0; int ret; DECLARE_BITMAP(test_map, TEST_MAX_BITS); u64 nr; if (vcpu->vcpu_id != 0) return; if (counter == 0) { ++counter; bitmap_zero(test_map, TEST_MAX_BITS); ret = test_bit(5, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(5, test_map); ret = test_bit(5, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); ret = test_bit(6, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); ret = test_bit(512, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(512, test_map); ret = test_bit(512, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); nr = 448; ret = test_bit(nr, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(nr, test_map); ret = test_bit(nr, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); } } ``` So why will test_bit() behave differently? Thanks very much! Regards, Le Tan

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Tracing built-in drivers ?
by Jay Aurabind Dec. 9, 2015

Dec. 9, 2015

Hi, I know I can use ftrace or perf to do tracing on modules that I can load from the userspace. But what if I want to do tracing on a driver which is built in ? For example, i915. There wouldnt be any userspace to trigger a trace when it does an init. Even if I recompile i915 as a module, I am not able to unload it. Are there any specific tools or techniques for doing this ? -- Thanks and Regards, Aurabindo J

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What are the differences between the -next tree and the -mm tree?
by Hao Lee Dec. 9, 2015

Dec. 9, 2015

Hi, I'm sorry to bother you to ask some questions about -next tree and -mm tree. I have read some documents about kernel trees, but I don't know the difference between the -next tree and -mm tree. In this post: http://lists.kernelnewbies.org/pipermail/kernelnewbies/2013-October/009145.… It seems that the -mm tree has been substituted by the -next tree. Besides, I can't find -mm tree in anywhere. So, could you explain the difference between the two trees. Regards, HaoLee

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if i want powerpc "local bus" support, must i select CONFIG_FSL_LBC?
by Robert P. J. Day Dec. 7, 2015

Dec. 7, 2015

trying to make a long story short, was handed an aging powerpc MPC8360e system on which to place linux, along with a BSP that does in fact generate a bootable kernel and filesystem. however, according to this online page (and i am *not* in any way a powerpc expert): http://cache.freescale.com/files/netcomm/doc/fact_sheet/MPC8360EFS.pdf this processor has something called a "local bus", off of which on this board hang things like DSP, FPGA and other things. during boot, i can see absolutely no mention of any of the devices attached to this local bus, or even that the bus itself is recognized, then i noticed that the .config file used to build this 3.14.29 kernel does not select what looks like the appropriate kernel option FSL_LBC. if anyone out there is a powerpc expert, can you confirm that you need to select that option (and hence compile in the source file arch/powerpc/sysdev/fsl_lbc.c) to get that support? i'm puzzled only because, if that file is required for local bus support, the people who gave us the BSP really should have turned it on. thanks for any guidance. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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How to correctly decode fun+X/Y
by Matwey V. Kornilov Dec. 7, 2015

Dec. 7, 2015

Hello, I have the following stack trace: [ 1351.381696] a.out S c0afb050 0 1676 1658 0x00000000 [ 1351.387048] [<c0afb050>] (__schedule) from [<c0afb4d0>] (schedule+0x58/0xcc) [ 1351.392436] [<c0afb4d0>] (schedule) from [<c069369c>] (tty_port_block_til_ready+0x1a8/0x35c) [ 1351.396937] [<c069369c>] (tty_port_block_til_ready) from [<c06ab220>] (uart_open+0x118/0x158) [ 1351.402560] [<c06ab220>] (uart_open) from [<c068b768>] (tty_open+0x11c/0x600) [ 1351.407043] [<c068b768>] (tty_open) from [<c03e1ce4>] (chrdev_open+0xb4/0x188) [ 1351.412556] [<c03e1ce4>] (chrdev_open) from [<c03db3dc>] (do_dentry_open+0x230/0x330) [ 1351.417038] [<c03db3dc>] (do_dentry_open) from [<c03dc64c>] (vfs_open+0x64/0x6c) [ 1351.422470] [<c03dc64c>] (vfs_open) from [<c03eaf5c>] (do_last+0x510/0xd94) [ 1351.426909] [<c03eaf5c>] (do_last) from [<c03eb86c>] (path_openat+0x8c/0x270) [ 1351.432398] [<c03eb86c>] (path_openat) from [<c03ecd78>] (do_filp_open+0x70/0xd4) [ 1351.436815] [<c03ecd78>] (do_filp_open) from [<c03dc9cc>] (do_sys_open+0x120/0x1e4) [ 1351.442117] [<c03dc9cc>] (do_sys_open) from [<c03dcab8>] (SyS_open+0x28/0x30) [ 1351.447046] [<c03dcab8>] (SyS_open) from [<c021cd40>] (ret_fast_syscall+0x0/0x34) Could please explain, how to correctly decode tty_port_block_til_ready+0x1a8/0x35c to the instruction or line of code using gdb? I have kernel image and separate debug info.

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wipe framebuffer with dd command
by Ran Shalit Dec. 5, 2015

Dec. 5, 2015

Hello, I would like to ask what is the effect of wiping frame buffer (dd if=/dev/zero of=/dev/fb0) ? I have some issue with framebuffer timing on LCD 240x320. I could not find a timing with width=240, height=320 which result in stable picture, but the following timing gave me stable ppicture with LCD: Pixel clock=6500 Width=240 Height=512 <<------------- instead of 320 !! Hfp=1 Hbp=100 HSW=14 Vfp=1 Vbp=1 VSW=10 The only strange thing is that I had to use height 512 instead of 320. When I try to render image it is stable but it starts in different line every time. And here comes the important part: After doing: dd if=/dev/zero of=/dev/fb0 It resolved the issue , and a new image starts from line 0. I don't understand why. Does anyone have any idea ? Do you think I still have a timing problem with LCD ? Regards, Ran

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cache maintenance for device memory
by Random Guy Dec. 5, 2015

Dec. 5, 2015

Hi, I have a device with a piece of RAM. That memory is accessible to CPU. I write a driver for that device and it maps device memory directly to userspace processes. This mapping is cacheable. So far so good. Now I'd like to flush or invalidate cache on specific parts of that memory. If it was just normal system memory I could use streaming DMA API: dma_map_*/dma_sync_*/dma_unmap_*. But the device memory is not a part of system memory and so there are no struct page for its pages, and thus streaming DMA support functions don't work. Is there anything wrong with my setup? What should I use to maintain caches for device memory? TIA

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Re: cache maintenance for device memory
by Random Guy Dec. 5, 2015

Dec. 5, 2015

Hi syed, thanks for your response. On Fri, Dec 4, 2015 at 9:16 AM, sk.syed2 <sk.syed2(a)gmail.com> wrote: >> I have a device with a piece of RAM. That memory is accessible to CPU. >> I write a driver for that device and it maps device memory directly to >> userspace processes. This mapping is cacheable. So far so good. >> > How did you map this device memory? Using ioremap? What platform is this? No, I provide mmap for the device file and then I do remap_pfn_range using vma->vm_pgoff as an offset into the device memory block. That's custom R&D ARM-based thing. >> Now I'd like to flush or invalidate cache on specific parts of that memory. >> If it was just normal system memory I could use streaming DMA API: >> dma_map_*/dma_sync_*/dma_unmap_*. But the device memory is not >> a part of system memory and so there are no struct page for its pages, >> and thus streaming DMA support functions don't work. > > Once you map the io memory, you get VAs for that memory and you should be able > to use dma_sync APIs. I've looked at the following function calls: arm_dma_sync_single_for_cpu -> dma_cache_maint_page -> __dma_page_dev_to_cpu and I see them mapping DMA handle to struct page and using that struct page. I'm sure that will not work, because as I said the device memory is not covered by struct page's.

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