November 2017 - kernelnewbies@kernelnewbies.org

where is __percpu_seg initialized?
by 落痕 March 28, 2018

March 28, 2018

Hi all: I knew the kernel implement the per-cpu variable via __percpu_seg. For example on x86 architecture, it's defined as: #ifdef CONFIG_X86_64 #define __percpu_seg gs #define __percpu_mov_op movq #else #define __percpu_seg fs #define __percpu_mov_op movl #endif But I'm curious where __percpu_seg is initialized?? I fail to find the relative code. Thanks.

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SD card wont work with dw_mmc driver in linux. Error -84 EILSEQ
by John Smith Dec. 2, 2017

Dec. 2, 2017

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Public Kernel Development
by Chris Obbard Dec. 2, 2017

Dec. 2, 2017

Hi list, Currently I am writing drivers for ARM boards (think along the lines of Raspberry Pi HATs, it doesn't belong in mainline; as well as other various hacks), which just consist of series of patches which I apply by checking out Mainline and then applying the patches by hand. Naturally, this is a bit of a hack... I want to have this as one repo on Github (or the like) with a _lot_ of branches with my changes in. This is what Git is made for, but what happens when Linus releases a new version? How do I make my changes apply to the new tag? Also, what happens if I want to pull from someone's -next repo, or pull in other patches? Maybe there is a tutorial somewhere that can help me. I am used to using Git for small projects :-). Cheers!

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completely disable an input device
by Crni Gorac Nov. 25, 2017

Nov. 25, 2017

The device in question is a touchpad. I tried first with disabling it in BIOS, but then learned that in this particular laptop, this setting is actually there just to let Windows know that touchpad is not to be used, and not actually physically turning it off. So I tried various options: 1. To blacklist corresponding module, psmouse in this case. This doesn't work for me, as I'd like to use the trackpoint, that is handled by the same module. 2. To delete corresponding /dev/input/mouseX and /dev/input/eventX devices. That doesn't work, as device nodes get recreated upon reboot. 3. To disable touchpad using corresponding userspace daemons: gpm for console and synclient for X. This is what I use at the moment, but I'd prefer to have it disabled on "lower level". 4. To write a small program that would grab corresponding /dev/input/mouseX device, through passing EVIOCGRAB to ioctl, and then sleep forever. This program would be activated through an udev rule. Haven't actually tried this, I think it should do, but it's too much work. So I'm wondering, is there any other way to accomplish this?

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How to debug when IRQs are disabled for few milliseconds?
by priyaranjan Nov. 22, 2017

Nov. 22, 2017

Hello All, I'm having issues on DRA7x based Android system. We have seen that that when we use 'cat' command in shell to dump some debug trace the 'shell' get scheduled in CPU0 and sometimes in CPU1. IRQs get blocked in the system for the amount of time the Shell runs. We have captured systrace which shows the same. Since we have some stringent requirement to service the IRQs within 2 miliisecond approx, we are missing the IRQs for important peripherals like Audio. I have tried the Hard lockup but the threshold can be programmed minimum to 1second hence could not succeed in this. I have also tried to use ftrace, however it was very difficult to find out where exactly the IRQs are getting disabled. Can anyone help? Regards, Priyaranjan

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kernel development cycle
by Tobin C. Harding Nov. 22, 2017

Nov. 22, 2017

Hi, Would someone please be able to expound on the stages of the kernel development cycle. In particular I would like to learn what a hobbyist kernel developer should be focusing their attention on during different stages of the cycle. In particular, what _not_ to do during certain stages of the cycle. Jonathan Corbet has mentioned that he is happy to take documentation patches during the merge window. Are other sub-systems open to patches during the merge window? My guess is not. Should one be focusing effort on bug fixing only (as opposed to new features) during rc1 and rc2? What about coverity fixes, are these most appreciated during early release candidates or are they better done against linux-next during later release candidates (so the bugs don't get into the mainline in the first place)? When are new feature patches best submitted? Or is all this not answerable because each maintainer/subsystem is different? Thanks in advance for your thoughts, Tobin.

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why iowrite32_rep() doesn't work, I have to use the iowrite32() with a loop
by ayaka Nov. 21, 2017

Nov. 21, 2017

Hello All: I am writing a driver, I need to write a series of values into the registers. The old code use the writel_relaxed() to avoid flushing cache between echo of register. I want to use the recommended way of the io operations, so I choose the iowrite32()_req(), but I found what it wrote nothing, I read it at once after a memory barrier, there is no contents there. But it I use the iowrite32() with a loop, it works well and the registers of the device is configured. What make this problem? The io memory is assigned with devm_ioremap_resource(). void mpp_dev_write_seq(struct rockchip_mpp_dev *mpp_dev, unsigned long offset, void *buffer, unsigned long count) { int i; #if 1 for (i = 0; i < count; i++) { u32 *cur = (u32 *)buffer; u32 pos = offset + i * 4; cur += i; mpp_debug(DEBUG_SET_REG, "write reg[%03d]: %08x\n", pos, *cur); iowrite32(*cur, mpp_dev->reg_base + pos); } #else iowrite32_rep(mpp_dev->reg_base + offset, buffer, count); mb(); for (i = 0; i < count; i++) { u32 cur = 0; u32 pos = offset / 4 + i; cur = ioread32(mpp_dev->reg_base + pos * 4); pr_info("get reg[%03d]: %08x\n", pos, cur); } #endif }

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RS-485 in half-duplex mode
by Oliver Graute Nov. 21, 2017

Nov. 21, 2017

Hello list, I try to use a RS-485 Interface with two wires on a imx28 CPU. Using the driver in mxs-auart.c. I already modified my device tree to use AUART4_RX and AUART4_TX for sending and receiving. This is working so far. But since it is half-duplex the question arises how the switching between sending and receiving is done. I have AUART4_RTS (GPIO2_26) for this purpose. Is this something the driver can handle? do I have to adjust my device tree or the driver for this setup? It is necessary to handle this via IOCTL(TIOCSRS485) from user space? Best Regards, Oliver

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mmap patch works in Virtualbox, not in QEMU
by Lev Olshvang Nov. 19, 2017

Nov. 19, 2017

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Installing man 9 pages for section kernel-api
by saketh Jakkula Nov. 19, 2017

Nov. 19, 2017

Hi I am trying to install manual pages for linux kernel apis. I have downloaded source file of version 4.12.1. I tried to install with the below commands make mandocs. But i am unable to see man pages for kernel-api. With some searching i found that i don't see kernel-api.tmpl in the source file. Can some one help to get that file or please provide instructions in installing man pages for kernel api. Thanks Saketh

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