[PATCH linux v2 1/3] drivers: misc: Character driver for seven segment display
Jaghathiswari Rankappagounder Natarajan
jaghu at google.com
Wed Nov 2 03:53:53 AEDT 2016
On Mon, Oct 17, 2016 at 12:55 PM, Rick Altherr <raltherr at google.com> wrote:
>
>
> On Mon, Oct 17, 2016 at 10:10 AM, Jaghathiswari Rankappagounder Natarajan
> <jaghu at google.com> wrote:
>
>> The character device driver implements the user-space API for letting
>> a user write to the display including any conversion methods necessary
>> to map the user input to a 7-segment display.
>>
>> Signed-off-by: Jaghathiswari Rankappagounder Natarajan <jaghu at google.com>
>> ---
>> drivers/misc/Kconfig | 5 ++
>> drivers/misc/Makefile | 1 +
>> drivers/misc/seven_seg_disp.c | 192 ++++++++++++++++++++++++++++++
>> ++++++++++++
>> drivers/misc/seven_seg_gen.h | 32 +++++++
>> 4 files changed, 230 insertions(+)
>> create mode 100644 drivers/misc/seven_seg_disp.c
>> create mode 100644 drivers/misc/seven_seg_gen.h
>>
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index 4617ddc..cf07817 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -804,6 +804,11 @@ config PANEL_BOOT_MESSAGE
>> An empty message will only clear the display at driver init
>> time. Any other
>> printf()-formatted message is valid with newline and escape
>> codes.
>>
>> +config SEVEN_SEGMENT_DISPLAY
>> + tristate "Character driver for seven segment display support"
>> + help
>> + Character driver for seven segment display support
>> +
>> config ASPEED_BT_IPMI_HOST
>> tristate "BT IPMI host driver"
>> help
>> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
>> index 724861b..718dc2b 100644
>> --- a/drivers/misc/Makefile
>> +++ b/drivers/misc/Makefile
>> @@ -57,4 +57,5 @@ obj-$(CONFIG_ECHO) += echo/
>> obj-$(CONFIG_VEXPRESS_SYSCFG) += vexpress-syscfg.o
>> obj-$(CONFIG_CXL_BASE) += cxl/
>> obj-$(CONFIG_PANEL) += panel.o
>> +obj-$(CONFIG_SEVEN_SEGMENT_DISPLAY) += seven_seg_disp.o
>> obj-$(CONFIG_ASPEED_BT_IPMI_HOST) += bt-host.o
>> diff --git a/drivers/misc/seven_seg_disp.c b/drivers/misc/seven_seg_disp.
>> c
>> new file mode 100644
>> index 0000000..88df4a0
>> --- /dev/null
>> +++ b/drivers/misc/seven_seg_disp.c
>> @@ -0,0 +1,192 @@
>> +/*
>> + * Seven segment display character driver
>> + * * Copyright (c) 2016 Google, Inc
>> + *
>> + * * This program is free software; you can redistribute it and/or modify
>> + * * it under the terms of the GNU General Public License version 2 as
>> + * * published by the Free Software Foundation.
>> + *
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/version.h>
>> +#include <linux/kernel.h>
>> +#include <linux/types.h>
>> +#include <linux/kdev_t.h>
>> +#include <linux/fs.h>
>> +#include <linux/uaccess.h>
>> +#include <linux/ctype.h>
>> +
>> +#include "seven_seg_gen.h"
>> +
>> +#define MAX_DISP_CHAR_SIZE 3
>> +
>> +#define LED_DOT 0x01
>> +
>> +/*
>> + * 0 1 2 3 4 5 6 7 8 9 A B C D E F
>> + * _ _ _ _ _ _ _ _ _ _ _ _
>> + * | | | _| _| |_| |_ |_ | |_| |_| |_| |_ | _| |_ |_
>> + * |_| | |_ _| | _| |_| | |_| | | | |_| |_ |_| |_ |
>> + *
>> + * data[7:1] = led[a:g]
>> + */
>> +const u8 seven_seg_bits[] = {
>> + 0xFC, 0x60, 0xDA, 0xF2, 0x66, 0xB6, 0xBE, 0xE0,
>> + 0xFE, 0xF6, 0xEE, 0x3E, 0x9C, 0x7A, 0x9E, 0x8E
>> + };
>> +
>> +/*
>> + * 0 1 2 3 4 5 6 7 8 9 A B C D E F
>> + * _ _ _ _ _
>> + * | |_ |_| |_ _ _ _ _ _ _ _ |_ _| _| | |
>> + * |_ |_ | | _| |_| |_| | |
>> + *
>> + * data[7:1] = led[a:g]
>> + */
>> +const u8 special_seven_seg_bits[] = {
>> + 0x00, 0x9C, 0x1E, 0xCE, 0x8E, 0x02, 0x02, 0x02,
>> + 0x02, 0x02, 0x02, 0x02, 0xB6, 0x7A, 0x7A, 0xEC
>> + };
>> +
>> +static dev_t seven_seg_devno;
>> +static struct class *seven_seg_disp_class;
>> +
>> +static int seven_seg_disp_open(struct inode *inode, struct file *filp)
>> +{
>> + struct seven_seg_disp_dev *disp_dev;
>> +
>> + disp_dev = container_of(inode->i_cdev,
>> + struct seven_seg_disp_dev, cdev);
>> + filp->private_data = disp_dev;
>> + return 0;
>> +}
>> +
>> +static int seven_seg_disp_close(struct inode *inode, struct file *filp)
>> +{
>> + filp->private_data = NULL;
>> + return 0;
>> +}
>> +
>> +static ssize_t seven_seg_disp_read(struct file *filp, char __user *buf,
>> size_t
>> + len, loff_t *off)
>> +{
>>
> May as well return the current value to them.
>
>
>> + return 0;
>> +}
>> +
>> +static u16 convert_to_disp_data(char *buf)
>> +{
>> + u8 low_display;
>> + u8 high_display;
>> + u16 led_value;
>> +
>> + low_display = seven_seg_bits[hex_to_bin(buf[2])];
>> +
>> + high_display = (buf[0] == '1') ?
>> + special_seven_seg_bits[hex_to_bin(buf[1])] :
>> + seven_seg_bits[hex_to_bin(buf[1])];
>> +
>> + led_value = low_display | (high_display << 8);
>> + if (buf[0] == '1') {
>> + led_value |= LED_DOT | (LED_DOT << 8);
>> + }
>> +
>> + return led_value;
>> +}
>> +
>> +static ssize_t seven_seg_disp_write(struct file *filp, const char __user
>> *buf,
>> + size_t len, loff_t *off)
>> +{
>> + char tmp[MAX_DISP_CHAR_SIZE];
>> + int length = len - 1;
>> + int i;
>> + u8 result;
>> +
>> + struct seven_seg_disp_dev *disp_dev;
>> +
>> + if (length != MAX_DISP_CHAR_SIZE) {
>> + return -EINVAL;
>> + }
>> +
>> + if (copy_from_user(tmp, buf, length) != 0) {
>> + return -EFAULT;
>> + }
>> +
>> + for (i = 0; i < MAX_DISP_CHAR_SIZE; i++) {
>>
> Only check the bytes actually provided by the user. If they do a 1-byte
> write, you'll read uninit data.
>
>
I am checking if the user is writing MAX_DISP_CHAR_SIZE data (3 bytes of
data) in the previous step (length != MAX_DISP_CHAR_SIZE).
Wanted to make sure user is writing 3 bytes of data so that conversion
could happen correctly.
+ if (!isxdigit(tmp[i]))
>> + return -EINVAL;
>> + }
>> +
>> + result = convert_to_disp_data(tmp);
>>
> Pick a more descriptive name than 'result' and 'tmp'. Describe what the
> variable contains.
>
>
>> +
>> + disp_dev = filp->private_data;
>> + disp_dev->update_seven_seg_data(&disp_dev->parent, result);
>> +
>> + return len;
>> +}
>> +
>> +static const struct file_operations seven_seg_disp_fops = {
>> +
>> + .owner = THIS_MODULE,
>> + .open = seven_seg_disp_open,
>> + .release = seven_seg_disp_close,
>> + .read = seven_seg_disp_read,
>> + .write = seven_seg_disp_write
>> +};
>> +
>> +void rem_cdev(struct seven_seg_disp_dev *disp_dev)
>> +{
>> + cdev_del(&disp_dev->cdev);
>> + device_destroy(seven_seg_disp_class, seven_seg_devno);
>> +}
>> +
>> +int setup_cdev(struct device parent,
>> + struct seven_seg_disp_dev *disp_dev,
>> + void (*update_disp_data)(struct device *, u16 data))
>> +{
>> + struct device *dev;
>> + int err;
>> +
>> + dev = device_create(seven_seg_disp_class, &parent,
>> seven_seg_devno,
>> + NULL, "seven_seg_disp_val");
>> + if (dev == NULL)
>> + return -1;
>> + disp_dev->parent = parent;
>> + disp_dev->dev = dev;
>> + disp_dev->update_seven_seg_data = update_disp_data;
>> + cdev_init(&disp_dev->cdev, &seven_seg_disp_fops);
>> + disp_dev->cdev.ops = &seven_seg_disp_fops;
>> + err = cdev_add(&disp_dev->cdev, seven_seg_devno, 1);
>> + if (err)
>> + device_destroy(seven_seg_disp_class, seven_seg_devno);
>> + return err;
>> +}
>> +
>> +static int __init seven_seg_disp_init(void)
>> +{
>> + if (alloc_chrdev_region(&seven_seg_devno, 0, 1, "disp_state") <
>> 0) {
>> + return -1;
>> + }
>> +
>> + seven_seg_disp_class = class_create(THIS_MODULE, "disp_state");
>> + if (seven_seg_disp_class == NULL) {
>> + goto unregister;
>> + return -1;
>> + }
>> +
>> +unregister:
>> + unregister_chrdev_region(seven_seg_devno, 1);
>> + return -1;
>> +}
>> +
>> +static void __exit seven_seg_disp_exit(void)
>> +{
>> + class_destroy(seven_seg_disp_class);
>> + unregister_chrdev_region(seven_seg_devno, 1);
>> +}
>> +
>> +module_init(seven_seg_disp_init);
>> +module_exit(seven_seg_disp_exit);
>> +MODULE_LICENSE("GPL");
>> +MODULE_AUTHOR("Jaghathiswari Rankappagounder Natarajan <jaghu at google.com
>> >");
>> +MODULE_DESCRIPTION("Seven segment display character driver");
>> diff --git a/drivers/misc/seven_seg_gen.h b/drivers/misc/seven_seg_gen.h
>> new file mode 100644
>> index 0000000..5748a18
>> --- /dev/null
>> +++ b/drivers/misc/seven_seg_gen.h
>>
>
> Why is this header a different name from the .c?
>
>
>> @@ -0,0 +1,32 @@
>> +/*
>> + * Seven segment display support
>> + * * Copyright (c) 2016 Google, Inc
>> + *
>> + * * This program is free software; you can redistribute it and/or modify
>> + * * it under the terms of the GNU General Public License version 2 as
>> + * * published by the Free Software Foundation.
>> + *
>> + */
>> +
>> +#ifndef SEVEN_SEG_H
>> +#define SEVEN_SEG_H
>>
>
> Guards don't match header name.
>
>
>> +
>> +#include <linux/device.h>
>> +#include <linux/cdev.h>
>> +
>> +#define DEFAULT_REFRESH_INTERVAL 1000
>>
>
> This doesn't seem to be used by any of the APIs provided.
>
If the refresh-interval-ms property is not provided in the device tree then
this value is used as default value(in file seven_seg_gpio.c)
> +
>> +struct seven_seg_disp_dev {
>> + struct device parent;
>> + struct device *dev;
>> + struct cdev cdev;
>> + void (*update_seven_seg_data)(struct device *, u16 data);
>> +};
>> +
>> +int setup_cdev(struct device parent,
>> + struct seven_seg_disp_dev *disp_dev,
>> + void (*update_disp_data)(struct device *, u16 data));
>>
>
> Way too generic of a method name. This name will be exposed in any .c
> that includes this header. Pick something that describes what it is doing
> _and_ what subsystem it belongs to.
>
>
>> +
>> +void rem_cdev(struct seven_seg_disp_dev *disp_dev);
>> +
>> +#endif
>> --
>> 2.8.0.rc3.226.g39d4020
>>
>>
>
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