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Re: Udev rule for USB keyboard
by Greg KH Aug. 5, 2016

Aug. 5, 2016

On Fri, Aug 05, 2016 at 04:02:59PM +0530, Madhu K wrote: > Just to understand how Udev rules works. You are going to have to provide more background, sorry, otherwise people are going to think that you are just asking here in order to do your "homework". sorry, greg k-h

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doubt on schedule_work() - work task getting scheduled lately
by Muni Sekhar Aug. 5, 2016

Aug. 5, 2016

Hi All, I have a doubt regarding the workqueue scheduling. I am using the workqueue for processing the Rx Interrupt data. I am calling schedule_work() on receiving the Rx interrupt from hardware. I calculated the time between calling the schedule_work() and workqueue task actually getting executed, Here I see many cases of less than 100 us(It is fairly good). But sometimes I see 10’s of ms and a lot in the 100’s of ms. I have seen over 0.5 secs too. I would like to know why does sometimes kernel takes longer time(in milli seconds) to schedule it? Is there any way to reduce this time gap? My code: static void my_workqueuetask(struct work_struct *work) { printk("In %s() \n",__func__); mutex_lock(&bh_mutex); //Do something here mutex_unlock(&bh_mutex); } static irqreturn_t my_irq_handler(int irq, void *dev) { ……; if(Rx Interrupt) schedule_work(&rx_work); return IRQ_HANDLED; } -- Thanks, Sekhar

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using sysctl.conf for module that initialize in early bootup
by Pankaj Gupta Aug. 5, 2016

Aug. 5, 2016

Dear All, I am trying to introduce a flag which controls probe of a driver that initialize in device_initcall(). I want to use a flag, if the flag is true driver will be initialed and if its false then probe will return without registering the driver. The value of flag can be changed at runtime and that should persist after reboot. I have searched and found about using /etc/sysctl.conf for this purpose. I observed that /etc is not mounted on system when device_initcall() executes. is there any other way by which i can implement this feature? Thanks & Regards, *Pankaj Gupta*

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Kexec rash kernel memory reservation
by Ronit Halder Aug. 5, 2016

Aug. 5, 2016

Hi, kexec reserves memory for loading crash kernel in the boot time for risk of DMA. I want to know, How kexec prevents allocation of memory which is adjacent to DMA memory? regards, Ronit

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spi device probe not carring device tree pointer, how to troubleshoot?
by Daniel. Aug. 4, 2016

Aug. 4, 2016

Hi everybody. I'm trying to get one of my drivers working on top of this[1]. My driver gets probed but spi->dev.of_node is NULL. Does anybody knows where spi->dev.of_node gets setted!? Here is a sample [2]. [1] https://github.com/daniel-santos/mcp2210-linux [2] https://gist.github.com/gkos/b54054b345afc4239e92f8adde99788e -- "Do or do not. There is no try" Yoda Master

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How to debug ethernet driver ?
by Ran Shalit Aug. 4, 2016

Aug. 4, 2016

Hello, I am writing ethernet network driver. I would like to ask if there are any steps which can help when debugging ethernet driver, or is it that the first test should already involve transmit/recieve packets to/from ip stack ? Any tips for debugging and testing a new ethernet driver will be appreciated, Thank you, Ran

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Kernel panic debugging
by Narasimha M Aug. 4, 2016

Aug. 4, 2016

Hi All, I am using linux-3.10.20 kernel and facing the below reported panic some times. As this is coming from general linux stack. Could you please guide how to debug these kind of panics. Call Trace: [<ffffffff801e64e8>] get_pageblock_flags_group+0xa8/0xd0 [<ffffffff801fd8a4>] suitable_migration_target+0x1c/0x68 [<ffffffff801fdf30>] compaction_alloc+0x1c0/0x258 [<ffffffff80227280>] migrate_pages+0xd0/0x570 [<ffffffff801fec00>] compact_zone+0x2c0/0x3c8 [<ffffffff801fef48>] compact_zone_order+0xa8/0xe0 [<ffffffff801ff0c8>] try_to_compact_pages+0x148/0x1b8 [<ffffffff807bec44>] __alloc_pages_direct_compact+0xd8/0x26c [<ffffffff801e8bec>] __alloc_pages_nodemask+0x3ec/0x788 [<ffffffff80171ca0>] copy_process.part.56+0x118/0x1180 [<ffffffff80172e34>] do_fork+0x9c/0x250 [<ffffffff8015cca4>] handle_sysn32+0x44/0x70 Thanks, Narasimha

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Kernel panic debugging
by Narasimha M Aug. 4, 2016

Aug. 4, 2016

Hi All, I am using linux-3.10.20 kernel and facing the below reported panic some times. As this is coming from general linux stack. Could you please guide how to debug these kind of panics. Call Trace: [<ffffffff801e64e8>] get_pageblock_flags_group+0xa8/0xd0 [<ffffffff801fd8a4>] suitable_migration_target+0x1c/0x68 [<ffffffff801fdf30>] compaction_alloc+0x1c0/0x258 [<ffffffff80227280>] migrate_pages+0xd0/0x570 [<ffffffff801fec00>] compact_zone+0x2c0/0x3c8 [<ffffffff801fef48>] compact_zone_order+0xa8/0xe0 [<ffffffff801ff0c8>] try_to_compact_pages+0x148/0x1b8 [<ffffffff807bec44>] __alloc_pages_direct_compact+0xd8/0x26c [<ffffffff801e8bec>] __alloc_pages_nodemask+0x3ec/0x788 [<ffffffff80171ca0>] copy_process.part.56+0x118/0x1180 [<ffffffff80172e34>] do_fork+0x9c/0x250 [<ffffffff8015cca4>] handle_sysn32+0x44/0x70 Thanks, Narasimha

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Dynamic Loading and unnloading of Device tree(dtb)
by Raul Piper Aug. 4, 2016

Aug. 4, 2016

Hi, Where can I find the example for the dynamic Loading of the device tree and its corresponding device driver. How can I build the dts with or without the kernel source. I am getting this error whenever I am trying to build the below sample dts file using the dtc compiler. dtc -O dtb -o leds-ns2.dtb leds-ns2.dts Error: leds-ns2.dts:1.1-2 syntax error FATAL ERROR: Unable to parse input tree Below is the content of the leds-ns2.dts #include <dt-bindings/leds/leds-ns2.h> ns2-leds { compatible = "lacie,ns2-leds"; blue-sata { label = "ns2:blue:sata"; slow-gpio = <&gpio0 29 0>; cmd-gpio = <&gpio0 30 0>; modes-map = <NS_V2_LED_OFF 0 1 NS_V2_LED_ON 1 0 NS_V2_LED_ON 0 0 NS_V2_LED_SATA 1 1>; }; }; Thanks, R

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Stupid question regarding bogomips and udelay()
by Aleksander Alekseev Aug. 3, 2016

Aug. 3, 2016

Hello Currently I'm reading Linux Kernel Development, 3rd Edition by Robert Love. Chapter 11 describes timers and udelay() procedure in particular. According to the book (if I didn't get anything wrong): * bogomips value (see `cat /proc/cpuinfo`) is determined only once during system boot * udelay() is implemented as busy loop where number of loops is calculated based on bogomips value [1][2] * udelay() guarantees that delay will be _at_least_ given number of usecs It's my understanding that it shouldn't work. CPU frequency actually changes manually (see cpufrequtils) and/or automatically depending for instance on laptop's current battery charge. There is also such a nasty thing as Intel Turbo Boost. In other words actual MIPS could be higher or lower than measured MIPS. So udealy() can't guarantee anything. Clearly I don't understand something. Could you please explain why udelay() supposed to work? [1] https://github.com/torvalds/linux/blob/master/arch/x86/lib/delay.c#L171 [2] https://github.com/torvalds/linux/blob/master/include/asm-generic/delay.h#L… -- Best regards, Aleksander Alekseev

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