Messages in this thread | | | Date | Wed, 1 Mar 2023 18:43:12 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCHv3 4/4] wiegand: add Wiegand GPIO bitbanged controller driver |
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On Wed, Mar 01, 2023 at 03:28:35PM +0100, Martin Zaťovič wrote: > This controller formats the data to a Wiegand format and bit-bangs > the message on devicetree defined GPIO lines. > > Several attributes need to be defined in the devicetree in order > for this driver to work, namely the data-hi-gpios, data-lo-gpios, > pulse-len, frame-gap and interval-len. These attributes are > documented in the devicetree bindings documentation files. > > The driver creates a dev file for writing messages on the bus. > It also creates a sysfs file to control the payload length of > messages(in bits). If a message is shorter than the set payload > length, it will be discarded. On the other hand, if a message is > longer, the additional bits will be stripped off.
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> +Date: January 2023
Blast from the past?
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> +config WIEGAND_GPIO > + tristate "GPIO-based wiegand master (write only)" > + depends on WIEGAND > + help > + This GPIO bitbanging Wiegand controller uses the libgpiod library to > + utilize GPIO lines for sending Wiegand data. Userspace may access > + the Wiegand GPIO interface via a dev entry.
What will be the name of the module if M?
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> +#include <linux/of.h>
No way.
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> +struct wiegand_gpio { > + struct device *dev; > + struct wiegand_controller *ctlr;
> + struct miscdevice misc_dev;
Make it first, same idea as per previous patch comments.
> + struct mutex mutex; > + struct gpio_desc *gpio_data_hi; > + struct gpio_desc *gpio_data_lo; > + struct file_operations fops;
> + u8 data[WIEGAND_MAX_PAYLEN_BYTES];
Have you considered DMA alignment? Is it a problem or not here?
> +};
...
> +static ssize_t store_ulong(u32 *val, const char *buf, size_t size, unsigned long max) > +{ > + int rc; > + u32 new;
> + if (max != 0 && new > max)
First part of the conditional is redundant. When you have such a user, you may add the restriction back.
> + return -EINVAL; > + > + *val = new; > + return size; > +}
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> +static struct attribute *wiegand_gpio_attrs[] = { > + &dev_attr_payload_len.attr, > + NULL,
No comma for the terminator entry.
> +}; > +
Redundant blank line.
> +ATTRIBUTE_GROUPS(wiegand_gpio);
...
> +void wiegand_gpio_send_bit(struct wiegand_gpio *wiegand_gpio, bool value, bool last) > +{ > + u32 pulse_len = wiegand_gpio->ctlr->pulse_len; > + u32 interval_len = wiegand_gpio->ctlr->interval_len; > + u32 frame_gap = wiegand_gpio->ctlr->frame_gap; > + struct gpio_desc *gpio = value ? wiegand_gpio->gpio_data_hi : wiegand_gpio->gpio_data_lo; > + > + gpiod_set_value_cansleep(gpio, 0); > + udelay(pulse_len); > + gpiod_set_value_cansleep(gpio, 1); > + > + if (last) > + udelay(frame_gap - pulse_len); > + else > + udelay(interval_len - pulse_len);
This is quite dangerous. You may end up with CPU 100% load for a long time without any way out. What is the range and why udelay() can't be replaced with usleep_range() for longer waits?
> +}
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> +/* This function is used for writing from file in dev directory */ > +static int wiegand_gpio_write_by_bits(struct wiegand_gpio *wiegand_gpio, u16 bitlen) > +{ > + size_t i; > + bool bit_value, is_last_bit; > + > + for (i = 0; i < bitlen; i++) { > + bit_value = ((wiegand_gpio->data[i / 8] >> (7 - (i % 8))) & 0x01);
Ah, your buffer should probably be a bitmap. Also consider bitmap_get_value8().
> + is_last_bit = (i + 1) == bitlen; > + wiegand_gpio_send_bit(wiegand_gpio, bit_value, is_last_bit); > + } > + > + return 0; > +} > + > +static ssize_t wiegand_gpio_get_user_data(struct wiegand_gpio *wiegand_gpio, char __user const *buf, > + size_t len) > +{ > + size_t rc; > + > + if (len > WIEGAND_MAX_PAYLEN_BYTES) > + return -EBADMSG;
> + rc = copy_from_user(&wiegand_gpio->data[0], buf, WIEGAND_MAX_PAYLEN_BYTES); > + if (rc < 0) > + return rc;
This is wrong. Homework: read the documentation and existing code to see why and how to fix.
> + return len; > +}
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> +static ssize_t wiegand_gpio_fwrite(struct file *filp, char __user const *buf, size_t len, > + loff_t *offset) > +{ > + struct wiegand_gpio_instance *info = filp->private_data; > + struct wiegand_gpio *wiegand_gpio = info->dev; > + u32 msg_length = wiegand_gpio->ctlr->payload_len; > + int rc; > + > + if (buf == NULL || len == 0 || len * 8 < msg_length)
!buf
DIV_ROUND_UP(msg_length / 8) > len
less overflow prone.
> + return -EINVAL; > + > + rc = wiegand_gpio_get_user_data(wiegand_gpio, buf, len); > + if (rc < 0) > + return rc; > + > + wiegand_gpio_write_by_bits(wiegand_gpio, msg_length); > + > + return len; > +}
> +static int wiegand_gpio_fopen(struct inode *ino, struct file *filp) > +{ > + int rc; > + struct wiegand_gpio_instance *info; > + struct wiegand_gpio *wiegand_gpio = container_of(filp->f_op, struct wiegand_gpio, fops); > + > + mutex_lock(&wiegand_gpio->mutex);
Can it be interrupted by a signal?
> + if ((filp->f_flags & O_ACCMODE) == O_RDONLY || (filp->f_flags & O_ACCMODE) == O_RDWR) { > + dev_err(wiegand_gpio->dev, "Device is write only\n"); > + rc = -EIO; > + goto err; > + } > + > + info = kzalloc(sizeof(*info), GFP_KERNEL); > + if (!info) { > + rc = -ENOMEM; > + goto err; > + } > + > + info->dev = wiegand_gpio; > + info->flags = filp->f_flags; > + mutex_unlock(&wiegand_gpio->mutex); > + > + filp->private_data = info; > + > + return 0; > +err: > + mutex_unlock(&wiegand_gpio->mutex); > + return rc; > +}
...
> + u8 msg_bytelength = (msg_bitlen % 8) ? (msg_bitlen / 8) + 1 : (msg_bitlen / 8);
DIV_ROUND_UP() (you will need math.h)
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> + if (dev->of_node) > + master->dev.of_node = device->dev.of_node;
No.
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> + if (status) > + return status;
What's this and why is it here? I'm afraid you haven't compiled this code... :-(
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> + master->transfer_message = &wiegand_gpio_transfer_message; > + master->payload_len = 26; /* set standard 26-bit format */
Can you replace master with some of the suggested words? Or is this a terminology from the specification of the bus?
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> + status = wiegand_gpio_request(dev, wiegand_gpio); > + if (status) { > + dev_err(wiegand_gpio->dev, "failed at requesting GPIOs\n"); > + return status;
return dev_error_probe();
Ditto for the rest.
> + }
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> + status = gpiod_direction_output(wiegand_gpio->gpio_data_hi, 1); > + status |= gpiod_direction_output(wiegand_gpio->gpio_data_lo, 1);
Huh?!
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> + wiegand_gpio->misc_dev.name = kasprintf(GFP_KERNEL, "wiegand-gpio%u", master->bus_num);
No checks?
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> + dev->groups = wiegand_gpio_groups;
Feels like this can be moved to dev_groups member of the struct driver.
> + > + return status; > +}
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> +static const struct of_device_id wiegand_gpio_dt_idtable[] = { > + { .compatible = "wiegand-gpio", },
> + {},
No comma for the terminator entry.
> +};
...
> +
Redundant blank line.
> +module_platform_driver(wiegand_gpio_driver);
-- With Best Regards, Andy Shevchenko
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