Re: [PATCH linux v2 1/3] drivers: misc: Character driver for seven segment display

[Rick Altherr <raltherr@google.com>]

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On Mon, Oct 17, 2016 at 10:10 AM, Jaghathiswari Rankappagounder Natarajan <
jaghu@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@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.


> +               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@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.


> +
> +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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