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want to clarify a couple things about initramfs
by Robert P. J. Day June 20, 2016

June 20, 2016

for the first time, i'm going to dive into the kernel support for initramfs, so i'll start with a couple questions. first, i note that the Doc file ramfs-rootfs-initramfs.txt seems(?) a bit dated, in that it refers to the 2.6 kernel, but it may just mean that it's relevant for 2.6 and everything newer, so it may be just fine, i guess i'll find out eventually. next (and possibly a silly question), i know that the primary(?) purpose of an initramfs is to load an early rootfs to get access to kernel modules, after which one tosses away the initramfs and mounts the "real" rootfs. but i'm pretty sure i have the right to build a kernel with enough of an initramfs that i can run off that embedded initramfs entirely out of RAM if all i want to do is, say, basic diagnostics. next, from the Doc file, i see the possibility of a second (external) initramfs: External initramfs images: -------------------------- If the kernel has initrd support enabled, an external cpio.gz archive can also be passed into a 2.6 kernel in place of an initrd. In this case, the kernel will autodetect the type (initramfs, not initrd) and extract the external cpio archive into rootfs before trying to run /init. This has the memory efficiency advantages of initramfs (no ramdisk block device) but the separate packaging of initrd (which is nice if you have non-GPL code you'd like to run from initramfs, without conflating it with the GPL licensed Linux kernel binary). It can also be used to supplement the kernel's built-in initramfs image. The files in the external archive will overwrite any conflicting files in the built-in initramfs archive. Some distributors also prefer to customize a single kernel image with task-specific initramfs images, without recompiling." is all that still accurate? again, i'm sure i can confirm that once i start digging through the code. in my case, i don't think i'll need an external initramfs if i can cram everything i need into the one embedded in the kernel. thoughts? 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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Coding style quesion
by Nicholas Mc Guire June 18, 2016

June 18, 2016

HI ! Stumbled across the somewhat inconsistent treatement of functions returning ERR_PTR() in the kernel with respect to coding style, while trying to write some static code checks. The two forms which seem comon are: if (PTR_ERR(var) == -EINVAL) { and if (var == ERR_PTR(-EINVAL)) { of which I think the first is the intended construct. my understanding of ERR_PTR is that it is intended to be used in the form ret = ERR_PTR(-EINVAL); ... retrurn ret; or return ERR_PTR(-EINVAL); but not as in the second if() above - technically its the same thing Is there an "official" preference to the one or other form ? thx! hofrat

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Re: kimage structure (Ronit Halder)
by harisha ja June 15, 2016

June 15, 2016

Hi Ronith, I think it forward declaration of the structure. that is is required because the below function uses that structure as parameter. 0 machine_kexec.c 50 void machine_kexec_cleanup(struct kimage *image) 1 machine_kexec.c 54 static void kexec_info(struct kimage *image) 2 machine_kexec.c 73 void machine_kexec(struct kimage *image) Thanks, Harish On Wed, Jun 15, 2016 at 9:30 PM, <kernelnewbies-request(a)kernelnewbies.org> wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Identifying whether a pci device is x1, x4, x8 or x16 > (John Chludzinski) > 2. Call Trace analysis doubt (Muni Sekhar) > 3. kimage structure (Ronit Halder) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 14 Jun 2016 17:46:13 -0400 > From: John Chludzinski <john.chludzinski(a)vivaldi.net> > Subject: Re: Identifying whether a pci device is x1, x4, x8 or x16 > To: Kevin Wilson <wkevils(a)gmail.com> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: <a1bd4a3fa6f9ca7ae1b8ab7ae0cf288e(a)mail.vivaldi.net> > Content-Type: text/plain; charset=US-ASCII; format=flowed > > Try: lshw > > On 2016-06-14 08:40, Kevin Wilson wrote: > > Hi all, > > Is there a way to find out whether a PCI device in a given Linux > > machine is x1, x4, x8 or x16, in terms > > of physical dimensions (without opening the box...) > > > > Regards, > > Kevin > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > ------------------------------ > > Message: 2 > Date: Wed, 15 Jun 2016 11:56:35 +0530 > From: Muni Sekhar <munisekharrms(a)gmail.com> > Subject: Call Trace analysis doubt > To: kernelnewbies(a)kernelnewbies.org > Message-ID: > < > CAHhAz%2BhvVefKi%2Bh7j_eed5DrKPkQKeF3aphnSyxcxEoUqMMG%2BA(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Hi, > > Let?s assume WARNING message says something like: > > > [ 0.000000] Call Trace: > > [ 0.000000] [<ffffffff81762590>] dump_stack+0x45/0x56 > > [ 0.000000] [<ffffffff8106dd2d>] warn_slowpath_common+0x7d/0xa0 > > [ 0.000000] [<ffffffff8106dde4>] warn_slowpath_fmt_taint+0x44/0x50 > > [ 0.000000] [<ffffffff8143329c>] ? acpi_tb_acquire_table+0x3e/0x6c > > [ 0.000000] [<ffffffff81765070>] warn_invalid_dmar+0x81/0x93 > > [ 0.000000] [<ffffffff81d8989d>] detect_intel_iommu+0xe9/0x172 > > [ 0.000000] [<ffffffff81d3c84f>] pci_iommu_alloc+0x4a/0x6c > > [ 0.000000] [<ffffffff81d4cb4b>] mem_init+0x17/0x9c > > [ 0.000000] [<ffffffff81d31e80>] start_kernel+0x23b/0x47d > > [ 0.000000] [<ffffffff81d31a4e>] ? set_init_arg+0x53/0x53 > > [ 0.000000] [<ffffffff81d31120>] ? early_idt_handlers+0x120/0x120 > > [ 0.000000] [<ffffffff81d315ee>] x86_64_start_reservations+0x2a/0x2c > > [ 0.000000] [<ffffffff81d31733>] x86_64_start_kernel+0x143/0x152 > > [ 0.000000] ---[ end trace c32c0e307381ad8a ]--- > > > > Few symbols in the above mentioned call trace are prefixed with ??? > (for e.g. ?early_idt_handlers\? set_init_arg\? > acpi_tb_acquire_table), what does it mean? > Does it needs to be considered while debugging the kernel module? > > > > Call Trace shows ?function+0xoffset/0xlength?. Does the > 0xoffset/0xlength changes if the module is built with ?g option and > without ?g option? > > > Thanks in Advance, > > -- > Thanks, > Sekhar > > > > ------------------------------ > > Message: 3 > Date: Wed, 15 Jun 2016 04:43:27 -0400 > From: Ronit Halder <ronit.crj(a)gmail.com> > Subject: kimage structure > To: kernelnewbies <kernelnewbies(a)kernelnewbies.org> > Message-ID: > < > CAAm8cU7-FJrg0Z3-DoR0bwzoH0az8%2BoFZmPBWY8d4C5nKUKoPw(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Hi, > There is a member in "struct kimage" called "entry" in kexec.h. > > What does entry represents? > > regards, > Ronit > > > > ------------------------------ > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > End of Kernelnewbies Digest, Vol 67, Issue 13 > ********************************************* >

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kimage structure
by Ronit Halder June 15, 2016

June 15, 2016

Hi, There is a member in "struct kimage" called "entry" in kexec.h. What does entry represents? regards, Ronit

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Re: Netlink Socket: trouble while using netlink_broadcast
by silky June 14, 2016

June 14, 2016

Did this work? Can you give me a working solution for this?

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Developing Linux Kernel Driver for LED Driver
by Raul Piper June 14, 2016

June 14, 2016

PS:Reposting it from the led-linux group to here. Hi, I am developing a Linux kernel driver(software) for a 16 channel LED driver(this driver here refers to the hardware of LED called LED Driver ) .Below are few of its characteristics DC input voltage range : 10 V to 28 V Integrated boost converter with adaptive output voltage 16 channels and independent PWM brightness control Up to 15 white LEDs per channel On-board microcontroller for total device control through 4-wire serial interface LED short-circuit faults management I have done some brute force work by creating a user space application to do some portion of the LED glowing, I know its not a full fledged work. I want to know on the below points : 1. How can I convert it into a GPIO driver and the standard Framework with which I can integrate it. 2.The architecture of the user space application to test this driver 3.The requirement for the Device Tree configuration for this. 4.The name of the LED class driver maintainer in the kernel linux, to whom I have to send the patch? 5.Any other mandatory requirement to which I have to adhere to for pushing the device driver to the main line. PS : I am using TI's beagleboard for developing the driver on the kernel 4.1x. Any reference example for such n channel Led driver will be helpful . Br, Rp

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Book Material
by akhilesh baddigam June 12, 2016

June 12, 2016

Grettings every one, I am new to linux kernel development, I started reading Robert loves Linux Kernel Development Book, The book is more theoretical I need to start linux kernel kernel programming, Can any one suggest me the best book or resource to start learning linux kernel programming. Thank you.

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list etiquette
by Tobin Harding June 12, 2016

June 12, 2016

LKML list etiquette question. When asking a [simple] question that receives an suitable answer is it correct etiquette to reply with a thank you email or is this just adding noise to the list? thanks, Tobin.

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gpio-mcp23s08 driver with multiple chips
by Nathan Williams June 9, 2016

June 9, 2016

Hi, I'm using the GPIO driver gpio-mcp23s08 for two MCP23S17 chips that use the same SPI chip select (and different addresses). My device tree contains: &spi0 { status = "okay"; bus-num = <0>; num-cs = <2>; cs-gpios = <&portc 2 0>, <&portc 3 0>; gpio@1 { compatible = "microchip,mcp23s17"; gpio-controller; #gpio-cells = <2>; microchip,spi-present-mask = <0x03>; reg = <1>; spi-max-frequency = <1000000>; }; }; Both gpiochips are registered and I can see them in /sys/class/gpio as gpiochip395 and gpiochip411. My problem is that I can't figure out which gpiochip is which. They both have the same label, ngpio and share the same of_node. Setting some GPIOs and probing the hardware helped me determine that gpiochip411 was the chip with addr = 0 and gpiochip395 was the chip with addr = 1. However I presume there is no guarantee on what base number is allocated to each chip? In fact, if I repeatedly unload and reload the driver each time the base numbers decrease until I eventually get the following warning: [ 3376.068639] gpiochip_find_base: cannot find free range [ 3376.073766] gpiochip_add_data: GPIOs 0..15 (mcp23s17) failed to register [ 3376.080474] ------------[ cut here ]------------ [ 3376.085105] WARNING: CPU: 1 PID: 807 at drivers/base/core.c:251 device_release+0x8c/0x90 [ 3376.093159] Device 'gpiochip29' does not have a release() function, it is broken and must be fixed. [ 3376.102174] Modules linked in: gpio_mcp23s08(+) [last unloaded: gpio_mcp23s08] [ 3376.109420] CPU: 1 PID: 807 Comm: modprobe Not tainted 4.7.0-rc2 #10 [ 3376.115744] Hardware name: Altera SOCFPGA [ 3376.119766] [<c010f780>] (unwind_backtrace) from [<c010b864>] (show_stack+0x10/0x14) [ 3376.127487] [<c010b864>] (show_stack) from [<c02c20f8>] (dump_stack+0x8c/0xa0) [ 3376.134685] [<c02c20f8>] (dump_stack) from [<c011c434>] (__warn+0xec/0x104) [ 3376.141619] [<c011c434>] (__warn) from [<c011c484>] (warn_slowpath_fmt+0x38/0x48) [ 3376.149074] [<c011c484>] (warn_slowpath_fmt) from [<c0324798>] (device_release+0x8c/0x90) [ 3376.157223] [<c0324798>] (device_release) from [<c02c40e0>] (kobject_put+0xb4/0xec) [ 3376.164858] [<c02c40e0>] (kobject_put) from [<bf04ef74>] (mcp23s08_probe+0x2c0/0x318 [gpio_mcp23s08]) [ 3376.174055] [<bf04ef74>] (mcp23s08_probe [gpio_mcp23s08]) from [<c035b7c8>] (spi_drv_probe+0x7c/0xa8) [ 3376.183245] [<c035b7c8>] (spi_drv_probe) from [<c0328be0>] (driver_probe_device+0x224/0x2bc) [ 3376.191653] [<c0328be0>] (driver_probe_device) from [<c0328d30>] (__driver_attach+0xb8/0xbc) [ 3376.200057] [<c0328d30>] (__driver_attach) from [<c0326f18>] (bus_for_each_dev+0x68/0x9c) [ 3376.208203] [<c0326f18>] (bus_for_each_dev) from [<c0328068>] (bus_add_driver+0x1a4/0x21c) [ 3376.216437] [<c0328068>] (bus_add_driver) from [<c0329694>] (driver_register+0x78/0xf8) [ 3376.224414] [<c0329694>] (driver_register) from [<bf052014>] (init_module+0x14/0x50 [gpio_mcp23s08]) [ 3376.233513] [<bf052014>] (init_module [gpio_mcp23s08]) from [<c0101780>] (do_one_initcall+0x40/0x174) [ 3376.242698] [<c0101780>] (do_one_initcall) from [<c01c9c50>] (do_init_module+0x64/0x394) [ 3376.250763] [<c01c9c50>] (do_init_module) from [<c018ceb4>] (load_module+0x1a60/0x206c) [ 3376.258736] [<c018ceb4>] (load_module) from [<c018d60c>] (SyS_init_module+0x14c/0x15c) [ 3376.266624] [<c018d60c>] (SyS_init_module) from [<c0107680>] (ret_fast_syscall+0x0/0x3c) [ 3376.274700] ---[ end trace 3a4ba228e00948b3 ]--- [ 3376.279316] mcp23s08: probe of spi0.1 failed with error -28 Ultimately I'd like to be able to use gpio-line-names in the device tree to name each of the GPIOs I'll be using in user space. To support multiple chips on the same SPI chip select I came up with this patch: --- a/drivers/gpio/gpio-mcp23s08.c +++ b/drivers/gpio/gpio-mcp23s08.c @@ -552,6 +552,7 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev, { int status; bool mirror = false; + struct device_node *np; mutex_init(&mcp->lock); @@ -566,7 +567,24 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev, mcp->chip.dbg_show = mcp23s08_dbg_show; #ifdef CONFIG_OF mcp->chip.of_gpio_n_cells = 2; - mcp->chip.of_node = dev->of_node; + for_each_child_of_node(dev->of_node, np) { + const __be32 *reg; + int len; + int a_cells, s_cells; + + reg = of_get_property(np, "reg", &len); + if (!reg) + continue; + + a_cells = of_n_addr_cells(np); + s_cells = of_n_size_cells(np); + + if (of_read_number(reg, a_cells) == cs) { + mcp->chip.of_node = np; + } + } + if (!mcp->chip.of_node) + mcp->chip.of_node = dev->of_node; #endif switch (type) { This allows me to use something like this in my device tree: gpio@1 { compatible = "microchip,mcp23s17"; gpio-controller; #gpio-cells = <2>; microchip,spi-present-mask = <0x03>; reg = <1>; spi-max-frequency = <1000000>; chip@0 { reg = <0>; gpio-line-names = "RLY_CTRL3", /* GPA0 */ ... chip@1 { reg = <1>; gpio-line-names = "USBA_PWR", /* GPA0 */ ... Which displays the names correctly with lsgpio, however I'm still stuck on how to figure out which base number to use when I want to export one of these GPIOs. Regards, Nathan

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How to find out if kernel or udev created a device node in Android
by Munagala Naresh June 8, 2016

June 8, 2016

Hi team, Is there a way to find if kernel or udev created a device node (@ /dev/xxxx) in Android? I searched in the internet and "udevadm" can be used to finf it but this is not available in Android. Please let me know if there is any alternative way to find it. -- Regards Naresh Babu 09900139337

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