June 2014 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Disabling a BH : spin_lock_bh or local_bh_disable.
by priyaranjan June 13, 2014

June 13, 2014

Hi All, I was referring to "Unreliable Guide To Locking by Paul Rusty Russell". Here is a quote below :- "If a bottom half shares data with user context, you have two problems. Firstly, the current user context can be interrupted by a bottom half, and secondly, the critical region could be entered from another CPU. This is where spin_lock_bh() (include/linux/spinlock.h) is used. It disables bottom halves on that CPU, then grabs the lock. spin_unlock_bh() does the reverse" Note : - "user context" here means : The kernel executing on behalf of a particular process or kernel thread (given by the current() macro.) Not to be confused with userspace. Can be interrupted by software or hardware interrupts. I have below questions related to the same. 1. If the BH is a tasklet/workque and in the user context we disable it, what happens when a interrupt(tied to the same tasklet/workque) occurs ? I hope the spin_lock_bh() do not disable the interrupt. 2. I hope that the spin_lock_bh needs to be acquired by the user context. Can anybody confirm this? How the critical section is achieved from the BH in the same context? 3.Overall It would be great if anybody can help me understand what happens when a BH is disabled with Interrupts still enabled for the BH. Regards, Priyaranjan

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why a static function is in kernel symbol table
by Ji Li June 13, 2014

June 13, 2014

Hi all, I happened to find that a static function show up in kernel symbol table: static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, int push_one, gfp_t gfp); I feel puzzled. The only difference between this function with other static functions in net/ipv4/tcp_output.c is that tcp_write_xmit is declared at the very beginning of the file. However, I tried putting declaration of another static function in front of tcp_write_xmit, but it still did not show up in newly compiled vmlinux. Could anyone kindly cast some light? Thanks Ji

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Re: Eudyptula Challenge Task 01
by me storage June 13, 2014

June 13, 2014

For Email Client Try to read the Documentation of kernel.org https://www.kernel.org/doc/Documentation/email-clients.txt Hi, > Which email client is best to submit tasks . I use gmail , and I get a > problem with attachment base64!? > > What you suggest me to use! > > Regards, > N.G > > On Tue, Apr 29, 2014 at 6:34 PM, Pranay Srivastava <pranjas(a)gmail.com> > wrote: > > On Tue, Apr 29, 2014 at 8:40 PM, me storage <me.storage126(a)gmail.com> > wrote: > >> Hi i every one i am new to linux kernel programming .I am participating > in > >> Eudyptula Challenge .Recently i submitted my solutions to Task 01 but i > >> gives me reply like the below > >> > >> "Please read the requirements for the Makefile and allow the module to > be > >> built against any kernel source tree on the filesystem, not just those > >> kernels that happened to be installed in /lib/ at some point in time." > >> > >> And my make file is like this > >> > >> ifneq ($(KERNELRELEASE),) > >> obj-m += helloworld.o > >> else > >> default > > > > I hope you understand the -C switch > > : > >> make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules > >> clean: > >> make -C /lib/modules/$(shell uname -r)/bulid M=$(PWD) clean > >> end > >> > > > > If not then find it out and see what you need to change. > > > >> > >> So can any please tell me how to allow the module to be built against > any > >> kernel source tree on the filesystem? > >> or can any one pleae tell me what does it mean? > >> Thank you > >> >

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git merge issues
by Raghavendra June 12, 2014

June 12, 2014

Hello everyone, Assume that i have two branches in my repository: master and devel. -- I've updated the master branch from the remote repository (using git pull). Assume that the file name 'file.txt' has gone through an update. -- Now the same file has also gone through a modification in the devel branch (manual editing) -- Now when I do a 'git merge master' from my devel branch, I am facing a conflict issue something like this : Auto-merging file.txt CONFLICT (content): Merge conflict in file.txt Automatic merge failed; fix conflicts and then commit the result. Now my question is that do I need to solve the merging issue manually or is there any way to solve this using git? Thank you. Raghavendra ------------------------------------------------------------------------------------------------------------------------------- [ C-DAC is on Social-Media too. Kindly follow us at: Facebook: https://www.facebook.com/CDACINDIA & Twitter: @cdacindia ] This e-mail is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email is strictly prohibited and appropriate legal action will be taken. -------------------------------------------------------------------------------------------------------------------------------

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Re: SOC: Zedboard: Driver question
by priyaranjan June 12, 2014

June 12, 2014

On Thu, Jun 12, 2014 at 8:13 PM, amit mehta <gmate.amit(a)gmail.com> wrote: > On Thu, Jun 12, 2014 at 4:52 PM, priyaranjan <priyaranjan45678(a)gmail.com> > wrote: > > > > > > > > On Thu, Jun 12, 2014 at 7:09 PM, amit mehta <gmate.amit(a)gmail.com> > wrote: > >> > >> We are working on a school project in which we are trying to develop a > >> audio mixer > >> on Zedboard (Development board from Digilent). We have developed the IP > >> and have > >> integrated it with the overall hardware using Programmable logic. This > >> board has ARM > >> core. We have a Digilent pre-configured Linux source which we > >> cross-compiled > >> for ARM board, device tree blob and bootloader for Zync(BOOT.BIN). The > >> system > >> boots fine with Linux, but now to expose the recently added hardware > >> implementation > >> of audio mixer, we are trying to develop the driver using the platform > >> driver API. > >> Currently, In our reconfigurable hardware, we have 2 channels and a > mixer > >> and we > >> want to access those individually as some file nodes under /proc FS. The > >> sample > >> code is shown below: > >> > >> <snip from myiir.c> > >> /* device match table to match with device node in device tree > >> * These are the list of devices that we want to expose as platform > device > >> */ > >> static const struct of_device_id myiir_of_match[] __devinitconst = { > >> {.compatible = "dglnt,myiir-audio-ch0"}, > >> {.compatible = "dglnt,myiir-audio-ch1"}, > >> {.compatible = "dglnt,myiir-audio-mix0"}, > >> {}, > >> }; > >> > >> MODULE_DEVICE_TABLE(of, myiir_of_match); > >> > >> /* platform driver structure for myiir driver */ > >> static struct platform_driver myiir_driver = { > >> .driver = { > >> .name = DRIVER_NAME, > >> .owner = THIS_MODULE, > >> .of_match_table = myiir_of_match}, > >> .probe = myiir_probe, > >> .remove = __devexit_p(myiir_remove), > >> .shutdown = __devexit_p(myiir_shutdown) > >> }; > >> > >> /* Register myiir platform driver */ > >> module_platform_driver(myiir_driver); > >> <myiir.c> > >> > >> Now, inside the probe routine (myiir_probe), can we create proc > >> entries by calling > >> create_proc for each of these nodes and setting the appropriate read and > >> write > >> methods(file_operations) ? > > > > > > > > Yes, I feel this is fine, the proc entries to be created in probe, > > Initialize all data structures as required in probe. > > > Thank you for this confirmation. I've one more query regarding the > IO addresses. The CAD tool from Xilinx shows the base addresses > of our custom IP, which we have put into the device tree blob(also > shown in the attached screeshot) and in our driver, we are requesting > the memory region and after calling the ioremap, we access those > IO addresses, but is there are need to write the register addresses > in the device tree file in a particular order(asceding/descending) ? > I am not sure about ascending or descending order but yes, the register addresses should be in the device tree. You can check more examples on the same and follow. > <snip from device tree file> > myiir-aud-ch0 { > compatible = "dglnt,myiir-audio-ch0"; > reg = <0x74200000 0x10000>; > }; > myiir-aud-ch1 { > compatible = "dglnt,myiir-audio-ch1"; > reg = <0x74220000 0x10000>; > }; > myiir-aud-mix0 { > compatible = "dglnt,myiir-audio-mix0"; > reg = <0x68600000 0x10000>; > }; > <snip from device tree file> > The sequence of operation in probe routine is: > > platform_get_resource(pdev, IORESOURCE_MEM, 0); > remap_size = res->end - res->start + 1; > request_mem_region(res->start, remap_size, pdev->name); > base_addr = ioremap(res->start, remap_size); > > Thanks, > Kumar >

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Problem using git
by Ali Aminian June 12, 2014

June 12, 2014

Hello The kernel tar file from "www.kernel.org" is around 70MB. but when i want to download the kernel using git it seems it's really huge. git shows 1% for 25MB. Is it how it should be or am i missing something? the git command i used is this: "git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git"

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EudyptulaChallenge in github??
by Sudip Mukherjee June 11, 2014

June 11, 2014

Hi Varka Bhadram , Rules of the Eudyptula Challenge says that you really should be doing your own work . So I will request you not to post the completed tasks in https://github.com/Bhadram/EudyptulaChallenge . It will not help anyone if they already have the code of the task. Anyways, congratulation on completing the task 1 . Thanks

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Beginner guide
by Prudhvee Narasimha Sadha June 11, 2014

June 11, 2014

Hi, My name is Prudhvee and I'm purusing my undergraduate second year. I'm intrested in kernel development but I'm unable to understand how to get into it. Can you please help me to become a kernel developer. I just want to know what I should learn and any suggested books to learn kernel programming. Thank you, Prudhvee.

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Patch submission issue
by Raghavendra June 11, 2014

June 11, 2014

Hello, I am new to the kernel development community and I started off by fixing small coding style errors in the drivers/staging directory. I've created a patch for the same and sent it to the maintainer. The maintainer replied to me something like this : " Please don't do multiple things in the same patch, a single patch should only do 1 thing. So break this up into multiple patches. " And my patch looks something like this : From 7effd3d61c6ce08cd44df0a5ba3d1e9ac9ab5a98 Mon Sep 17 00:00:00 2001 From: Raghavendra <arrao(a)cdac.in> Date: Tue, 10 Jun 2014 22:04:52 +0530 Subject: [PATCH] Staging: rtl8192e: dot11d: Fixed coding style issues Replaced 'printk' with 'netdev_info' and 'netdev_err' wherever necessary. Also fixed the coding issue cooresponding to line gap after the declarations. Signed-off-by: Raghavendra <arrao(a)cdac.in> --- drivers/staging/rtl8192e/dot11d.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/staging/rtl8192e/dot11d.c b/drivers/staging/rtl8192e/dot11d.c index 53da610..ef9da86 100644 --- a/drivers/staging/rtl8192e/dot11d.c +++ b/drivers/staging/rtl8192e/dot11d.c @@ -49,6 +49,7 @@ static struct channel_list ChannelPlan[] = { void dot11d_init(struct rtllib_device *ieee) { struct rt_dot11d_info *pDot11dInfo = GET_DOT11D_INFO(ieee); + pDot11dInfo->bEnabled = false; pDot11dInfo->State = DOT11D_STATE_NONE; @@ -133,12 +134,12 @@ void Dot11d_UpdateCountryIe(struct rtllib_device *dev, u8 *pTaddr, pTriple = (struct chnl_txpow_triple *)(pCoutryIe + 3); for (i = 0; i < NumTriples; i++) { if (MaxChnlNum >= pTriple->FirstChnl) { - printk(KERN_INFO "Dot11d_UpdateCountryIe(): Invalid country IE, skip it........1\n"); + netdev_info(dev->dev, "Dot11d_UpdateCountryIe(): Invalid country IE, skip it........1\n"); return; } if (MAX_CHANNEL_NUMBER < (pTriple->FirstChnl + pTriple->NumChnls)) { - printk(KERN_INFO "Dot11d_UpdateCountryIe(): Invalid country IE, skip it........2\n"); + netdev_info(dev->dev, "Dot11d_UpdateCountryIe(): Invalid country IE, skip it........2\n"); return; } @@ -165,7 +166,7 @@ u8 DOT11D_GetMaxTxPwrInDbm(struct rtllib_device *dev, u8 Channel) u8 MaxTxPwrInDbm = 255; if (MAX_CHANNEL_NUMBER < Channel) { - printk(KERN_INFO "DOT11D_GetMaxTxPwrInDbm(): Invalid Channel\n"); + netdev_info(dev->dev, "DOT11D_GetMaxTxPwrInDbm(): Invalid Channel\n"); return MaxTxPwrInDbm; } if (pDot11dInfo->channel_map[Channel]) @@ -204,7 +205,7 @@ int ToLegalChannel(struct rtllib_device *dev, u8 channel) } if (MAX_CHANNEL_NUMBER < channel) { - printk(KERN_ERR "%s(): Invalid Channel\n", __func__); + netdev_err(dev->dev, "%s(): Invalid Channel\n", __func__); return default_chn; } -- 1.8.1.2 Can anyone please guide me through my mistake. Thank you. ------------------------------------------------------------------------------------------------------------------------------- [ C-DAC is on Social-Media too. Kindly follow us at: Facebook: https://www.facebook.com/CDACINDIA & Twitter: @cdacindia ] This e-mail is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email is strictly prohibited and appropriate legal action will be taken. -------------------------------------------------------------------------------------------------------------------------------

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Memory mapping issue in OMAP Linux kernel stack
by Saket Sinha June 11, 2014

June 11, 2014

HI, I am working on linux kernel MMC layer which is responsible for supporting SD/MMC cards on ARM platform. I am stuck with an issue related to TI OMAP driver in this layer. *Background of Problem* - OMAP is not SDHCI compliant In the mmc linux kernel driver stack, most of the drivers are sdhci compilant. All sdhci compliant drivers have a common code which is written in sdhci.c and a specific hardware dependent code which are present is files like tegra-sdhci.c for NVIDIA Tegra and sdhci-esdhc for Freescale iMX. *For NVIDIA Tegra* - http://lxr.free-electrons.com/source/drivers/mmc/host/sdhci-tegra.c *For Freescale iMX* – http://lxr.free-electrons.com/source/drivers/mmc/host/sdhci-esdhc-imx.c Since the present omap_hsmmc driver as of now is not sdhci complaint, it does all these tasks by itself as shown in the below link – http://lxr.free-electrons.com/source/drivers/mmc/host/omap_hsmmc.c *MY OBJECTIVE - MAKE OMAP SDHCI COMPLIANT* I need to get memory mapping of registers right. What I found was that the memory mapping defined in the SDHCI was not same as that of omap. So I wrote to TI but he said the registers are mapping, even the offsets are same. He gave me the example of these two registers from am335x TRM here- http://www.ti.com/lit/ug/spruh73j/spruh73j.pdf >From 18.5.1.10 in AM335x TRM: SD_CMD[31:16] = the command register. *SD_CMD[15:0] = the transfer mode* >From 18.5.1.17 *SD_HCTL[23:16] = Block gap control.* In the SDHCI spec given here - https://www.sdcard.org/downloads/pls/simplified_specs/archive/partA2_300.pdf these registers are having these memory address/offsets - *Transfer Mode Register (Offset 00Ch)* *Block Count Register (Offset 006h)* I am not able to figure out how these offsets are same. Can someone help me regarding this. Regards, Saket Sinha

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