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what is the purpose of "console_silent" in printk.h?
by rpjday＠crashcourse.ca Aug. 21, 2018

Aug. 21, 2018

i note in include/linux/printk.h: static inline void console_silent(void) { console_loglevel = CONSOLE_LOGLEVEL_SILENT; } except i see no reference to "console_silent" anywhere else in the entire kernel code base. any idea what its purpose is? rday

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GPIO consumer interface and DT
by Arkadiusz Lis Aug. 20, 2018

Aug. 20, 2018

Hi guys, I'd like emxx_udc driver to start using gpio consumer interface. I prepared draft of a patch and I have a question regarding obtaining gpio descriptor. So I use this: devm_gpiod_get(struct device *dev, const char *con_id, enum gpiod_flags flags), the second argument is con_id. What I learned from Documentation/driver-api/gpio/board.rst is this string should be equal to <function> prefix in <function>-gpios node in device tree. For example: in file drivers/i2c/busses/i2c-gpio.c author gets gpio descriptor with con_ids 'sda' and 'scl'. They are described in Documentation/devicetree/bindings/i2c/i2c-gpio.txt as required properties. In my case I didn't find bindings for emxx_udc driver and I don't know what string should I insert: gpiod = devm_gpiod_get(udc->dev, "DT_GPIOS_NAME", GPIOD_IN); // "DT_GPIOS_NAME" is a placeholder Do you know who defines bindings or how can I solve this issue? Maybe I'm searching in the wrong direction and this is not how it should be done? Comments and hints are very welcome Thanks, Arek --- >From 2afe158b9793f614518b1897d6f67d74f92bc95e Mon Sep 17 00:00:00 2001 From: Arkadiusz Lis <areklis909(a)gmail.com> Date: Wed, 15 Aug 2018 23:34:12 +0200 Subject: [PATCH] Staging: emxx_udc: start using gpio consumer interface Remove usages of old linux/gpio.h interface, instead prefer new linux/gpio/consumer.h Obtain gpio descriptor in probe(), port getting gpio value to more recent interface. Signed-off-by: Arkadiusz Lis <areklis909(a)gmail.com> --- drivers/staging/emxx_udc/emxx_udc.c | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/drivers/staging/emxx_udc/emxx_udc.c b/drivers/staging/emxx_udc/emxx_udc.c index 3e51476..fe8546a 100644 --- a/drivers/staging/emxx_udc/emxx_udc.c +++ b/drivers/staging/emxx_udc/emxx_udc.c @@ -27,7 +27,7 @@ #include <linux/usb/gadget.h> #include <linux/irq.h> -#include <linux/gpio.h> +#include <linux/gpio/consumer.h> #include "emxx_udc.h" @@ -57,7 +57,7 @@ /*===========================================================================*/ /* Global */ struct nbu2ss_udc udc_controller; - +static struct gpio_desc *gpiod; /*-------------------------------------------------------------------------*/ /* Read */ static inline u32 _nbu2ss_readl(void *address) @@ -2303,7 +2303,7 @@ static inline void _nbu2ss_check_vbus(struct nbu2ss_udc *udc) mdelay(VBUS_CHATTERING_MDELAY); /* wait (ms) */ /* VBUS ON Check*/ - reg_dt = gpio_get_value(VBUS_VALUE); + reg_dt = gpiod_get_value(gpiod); if (reg_dt == 0) { udc->linux_suspended = 0; @@ -2330,7 +2330,7 @@ static inline void _nbu2ss_check_vbus(struct nbu2ss_udc *udc) } } else { mdelay(5); /* wait (5ms) */ - reg_dt = gpio_get_value(VBUS_VALUE); + reg_dt = gpiod_get_value(gpiod); if (reg_dt == 0) return; @@ -2394,7 +2394,7 @@ static inline void _nbu2ss_int_usb_suspend(struct nbu2ss_udc *udc) u32 reg_dt; if (udc->usb_suspended == 0) { - reg_dt = gpio_get_value(VBUS_VALUE); + reg_dt = gpiod_get_value(gpiod); if (reg_dt == 0) return; @@ -2434,7 +2434,7 @@ static irqreturn_t _nbu2ss_udc_irq(int irq, void *_udc) struct nbu2ss_udc *udc = (struct nbu2ss_udc *)_udc; struct fc_regs *preg = udc->p_regs; - if (gpio_get_value(VBUS_VALUE) == 0) { + if (gpiod_get_value(gpiod) == 0) { _nbu2ss_writel(&preg->USB_INT_STA, ~USB_INT_STA_RW); _nbu2ss_writel(&preg->USB_INT_ENA, 0); return IRQ_HANDLED; @@ -2443,7 +2443,7 @@ static irqreturn_t _nbu2ss_udc_irq(int irq, void *_udc) spin_lock(&udc->lock); for (;;) { - if (gpio_get_value(VBUS_VALUE) == 0) { + if (gpiod_get_value(gpiod) == 0) { _nbu2ss_writel(&preg->USB_INT_STA, ~USB_INT_STA_RW); _nbu2ss_writel(&preg->USB_INT_ENA, 0); status = 0; @@ -2852,7 +2852,7 @@ static int nbu2ss_ep_fifo_status(struct usb_ep *_ep) preg = udc->p_regs; - data = gpio_get_value(VBUS_VALUE); + data = gpiod_get_value(gpiod); if (data == 0) return -EINVAL; @@ -2896,7 +2896,7 @@ static void nbu2ss_ep_fifo_flush(struct usb_ep *_ep) return; } - data = gpio_get_value(VBUS_VALUE); + data = gpiod_get_value(gpiod); if (data == 0) return; @@ -2938,7 +2938,7 @@ static int nbu2ss_gad_get_frame(struct usb_gadget *pgadget) } udc = container_of(pgadget, struct nbu2ss_udc, gadget); - data = gpio_get_value(VBUS_VALUE); + data = gpiod_get_value(gpiod); if (data == 0) return -EINVAL; @@ -2964,7 +2964,7 @@ static int nbu2ss_gad_wakeup(struct usb_gadget *pgadget) return -EINVAL; } - data = gpio_get_value(VBUS_VALUE); + data = gpiod_get_value(gpiod); if (data == 0) { dev_warn(&pgadget->dev, "VBUS LEVEL = %d\n", data); return -EINVAL; @@ -3224,6 +3224,11 @@ static int nbu2ss_drv_probe(struct platform_device *pdev) return status; } + gpiod = devm_gpiod_get(udc->dev, "DT_GPIOS_NAME", GPIOD_IN); + if(IS_ERR(gpiod)) { + dev_err(udc->dev, "failed to get gpio\n"); + return PTR_ERR(gpiod); + } /* Driver Initialization */ status = nbu2ss_drv_contest_init(pdev, udc); if (status < 0) { @@ -3314,7 +3319,7 @@ static int nbu2ss_drv_resume(struct platform_device *pdev) if (!udc) return 0; - data = gpio_get_value(VBUS_VALUE); + data = gpiod_get_value(gpiod); if (data) { udc->vbus_active = 1; udc->devstate = USB_STATE_POWERED; -- 1.9.1

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Difference between kernel logical address and kernel virtual address
by Abhinav Misra Aug. 19, 2018

Aug. 19, 2018

Hi, In LDD3 book at Ch-15 they mentioned all types of address used in the kernel. But wrt the book, not able to understand the difference between kernel logical and virtual address. Can somebody elaborate the same with some eg. BR,Abhinav

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System call vs POSIX call
by Subhashini Rao Beerisetty Aug. 17, 2018

Aug. 17, 2018

Hi All, I'm trying to get the difference between system call and POSIX call. System calls are user mode API's (open(), close(), ioctl(),...) gets the kernel service via software interrupt. What about POSIX calls and how it differs with the system call.? Can anyone clarify me on this.

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How to assess how much stack space kernel function may use?
by Lev Olshvang Aug. 16, 2018

Aug. 16, 2018

Hello all I am writing kernel module function that calls for vfs function , so I am not aware how deep kernel stack can grow due to my calls I need to take 512 bytes for some processing, and I know kernel stack is 4K only. My function is also part of calling chain, so I do not know how much stack is used before my function is called. What dara can I get from kernel during compilation and run about stack utiilizaton to help me in estimation ? Lev

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Is there any way to show local var when using crash to analyse coredump?
by Larry Aug. 16, 2018

Aug. 16, 2018

Hi list, When using gdb, we can use "frame" command to select which layer in the back trace to debug, and then we can use "print" command to print local var within this layer. But I found that these two commands does not work in crash tool, is there any way to solve it? Thanks Larry

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Proxy filesystems
by Demi Obenour Aug. 12, 2018

Aug. 12, 2018

How difficult would it be to create a proxy filesystem — that is, a filesystem that is a view of the filesystem? For instance, opening `/dev/urlfs/home/test/A%20Bcd` would open `/home/test/A Bcd`. The purpose would be to handle poorly written tools (like Autoconf and CMake) that do not handle wierd characters in filenames.

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A question on the function clean_bdev_bh_alias
by Larry Aug. 11, 2018

Aug. 11, 2018

Hello list, I'm confused with the function, could someone help?? Does it intend to remove existent pages in block device's page cache if some new page cache of a vfs file was created whose block number range has overlaps with its block device page cache? Thanks in advance. Best regards, Larry

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kobj->state_initialized is never set to 0
by Helen Koike Aug. 10, 2018

Aug. 10, 2018

Hi, I am simulating hotplugging a platform device (to the media/platform/vimc driver), so I register it using platform_device_register, then I unregister it with platform_device_unregister, then I register it again, but the code doesn't allow me to register something that was registered before due to this line: https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334 The variable kobj->state_initialized is set to 1 at https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194 but it is never set to 0 again. Is this how it is supposed to work? Or kobj->state_initialized is set to 0 somewhere else I couldn't find? Thanks Helen

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first patch question
by Greg Gallagher Aug. 10, 2018

Aug. 10, 2018

Hi, I creating my first patch to the kernel. I followed the instruction on the newbies wiki and everything went smoothly. I got feedback from the maintainer to fix all the alignment issues in the file instead of just the one i picked. My question is if I fix 10 alignment issues identified by checkpatch,pl should each fix be a separate commit? Should I have a 10 commit patch set for the 10 alignment issues or is it better to make them all one commit since all the commits are fixing alignment issues? Thanks for our time, Greg

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