Date:   Fri, 14 Aug 2020 21:31:29 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 07/20] gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL
 and GPIO_V2_LINE_GET_VALUES_IOCTL

On Fri, Aug 14, 2020 at 5:04 AM Kent Gibson <warthog618@...il.com> wrote:
>
> Add support for requesting lines using the GPIO_V2_GET_LINE_IOCTL, and
> returning their current values using GPIO_V2_LINE_GET_VALUES_IOCTL.
>
> Signed-off-by: Kent Gibson <warthog618@...il.com>
> ---

Hi Kent,

not many comments here, just a couple minor details below.

>
> The struct line implementation is based on the v1 struct linehandle
> implementation.
>
> The line_ioctl() is a simple wrapper around line_get_values() here, but
> will be extended with other ioctls in subsequent patches.
>
> Changes for v4:
>  - fix handling of mask in line_get_values
>
>  drivers/gpio/gpiolib-cdev.c | 413 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 413 insertions(+)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index 8b012879fe3f..8671e04ff989 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -1,7 +1,9 @@
>  // SPDX-License-Identifier: GPL-2.0
>
>  #include <linux/anon_inodes.h>
> +#include <linux/atomic.h>
>  #include <linux/bitmap.h>
> +#include <linux/build_bug.h>
>  #include <linux/cdev.h>
>  #include <linux/compat.h>
>  #include <linux/device.h>
> @@ -34,6 +36,7 @@
>   * GPIO line handle management
>   */
>
> +#ifdef CONFIG_GPIO_CDEV_V1
>  /**
>   * struct linehandle_state - contains the state of a userspace handle
>   * @gdev: the GPIO device the handle pertains to
> @@ -376,6 +379,390 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
>         linehandle_free(lh);
>         return ret;
>  }
> +#endif /* CONFIG_GPIO_CDEV_V1 */
> +
> +/**
> + * struct line - contains the state of a userspace line request
> + * @gdev: the GPIO device the line request pertains to
> + * @label: consumer label used to tag descriptors
> + * @num_descs: the number of descriptors held in the descs array
> + * @descs: the GPIO descriptors held by this line request, with @num_descs
> + * elements.
> + */
> +struct line {

How about line_request, line_request_data or line_req_ctx? Something
more intuitive than struct line that doesn't even refer to a single
line. Same for relevant functions below.

> +       struct gpio_device *gdev;
> +       const char *label;
> +       u32 num_descs;
> +       struct gpio_desc *descs[];
> +};
> +
> +#define GPIO_V2_LINE_BIAS_FLAGS \
> +       (GPIO_V2_LINE_FLAG_BIAS_PULL_UP | \
> +        GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN | \
> +        GPIO_V2_LINE_FLAG_BIAS_DISABLED)
> +
> +#define GPIO_V2_LINE_DIRECTION_FLAGS \
> +       (GPIO_V2_LINE_FLAG_INPUT | \
> +        GPIO_V2_LINE_FLAG_OUTPUT)
> +
> +#define GPIO_V2_LINE_DRIVE_FLAGS \
> +       (GPIO_V2_LINE_FLAG_OPEN_DRAIN | \
> +        GPIO_V2_LINE_FLAG_OPEN_SOURCE)
> +
> +#define GPIO_V2_LINE_VALID_FLAGS \
> +       (GPIO_V2_LINE_FLAG_ACTIVE_LOW | \
> +        GPIO_V2_LINE_DIRECTION_FLAGS | \
> +        GPIO_V2_LINE_DRIVE_FLAGS | \
> +        GPIO_V2_LINE_BIAS_FLAGS)
> +
> +static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
> +                                    int line_idx)
> +{
> +       int i;
> +       u64 mask = BIT_ULL(line_idx);
> +
> +       for (i = 0; i < lc->num_attrs; i++) {
> +               if ((lc->attrs[i].attr.id == GPIO_V2_LINE_ATTR_ID_FLAGS) &&
> +                   (lc->attrs[i].mask & mask))
> +                       return lc->attrs[i].attr.flags;
> +       }
> +       return lc->flags;
> +}
> +
> +static int gpio_v2_line_config_output_value(struct gpio_v2_line_config *lc,
> +                                           int line_idx)
> +{
> +       int i;
> +       u64 mask = BIT_ULL(line_idx);
> +
> +       for (i = 0; i < lc->num_attrs; i++) {
> +               if ((lc->attrs[i].attr.id == GPIO_V2_LINE_ATTR_ID_OUTPUT_VALUES) &&
> +                   (lc->attrs[i].mask & mask))
> +                       return !!(lc->attrs[i].attr.values & mask);
> +       }
> +       return 0;
> +}
> +
> +static int gpio_v2_line_flags_validate(u64 flags)
> +{
> +       /* Return an error if an unknown flag is set */
> +       if (flags & ~GPIO_V2_LINE_VALID_FLAGS)
> +               return -EINVAL;
> +
> +       /*
> +        * Do not allow both INPUT & OUTPUT flags to be set as they are
> +        * contradictory.
> +        */
> +       if ((flags & GPIO_V2_LINE_FLAG_INPUT) &&
> +           (flags & GPIO_V2_LINE_FLAG_OUTPUT))
> +               return -EINVAL;
> +
> +       /*
> +        * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
> +        * the hardware actually supports enabling both at the same time the
> +        * electrical result would be disastrous.
> +        */
> +       if ((flags & GPIO_V2_LINE_FLAG_OPEN_DRAIN) &&
> +           (flags & GPIO_V2_LINE_FLAG_OPEN_SOURCE))
> +               return -EINVAL;
> +
> +       /* Drive requires explicit output direction. */
> +       if ((flags & GPIO_V2_LINE_DRIVE_FLAGS) &&
> +           !(flags & GPIO_V2_LINE_FLAG_OUTPUT))
> +               return -EINVAL;
> +
> +       /* Bias requies explicit direction. */

s/requies/requires/

> +       if ((flags & GPIO_V2_LINE_BIAS_FLAGS) &&
> +           !(flags & GPIO_V2_LINE_DIRECTION_FLAGS))
> +               return -EINVAL;
> +
> +       /* Only one bias flag can be set. */
> +       if (((flags & GPIO_V2_LINE_FLAG_BIAS_DISABLED) &&
> +            (flags & (GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN |
> +                      GPIO_V2_LINE_FLAG_BIAS_PULL_UP))) ||
> +           ((flags & GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN) &&
> +            (flags & GPIO_V2_LINE_FLAG_BIAS_PULL_UP)))
> +               return -EINVAL;
> +
> +       return 0;
> +}
> +
> +static int gpio_v2_line_config_validate(struct gpio_v2_line_config *lc,
> +                                       int num_lines)

I recall sending some patches for gpiolib that would fix some
potential problems with casting between signed and unsigned integers.
I think they were of different size too though. I don't see any
potential problems here yet but maybe whenever an argument/local
variable can't take a negative value by design, let's use unsigned
int?

> +{
> +       int i, ret;

Same here and elsewhere for arguments and local variables.

> +       u64 flags;
> +
> +       if (lc->num_attrs > GPIO_V2_LINE_NUM_ATTRS_MAX)
> +               return -EINVAL;
> +
> +       if (memchr_inv(lc->padding, 0, sizeof(lc->padding)))
> +               return -EINVAL;
> +
> +       for (i = 0; i < num_lines; i++) {
> +               flags = gpio_v2_line_config_flags(lc, i);
> +               ret = gpio_v2_line_flags_validate(flags);
> +               if (ret)
> +                       return ret;
> +       }
> +       return 0;
> +}
> +
> +static void gpio_v2_line_config_flags_to_desc_flags(u64 flags,
> +                                                   unsigned long *flagsp)
> +{
> +       assign_bit(FLAG_ACTIVE_LOW, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_ACTIVE_LOW);
> +       if (flags & GPIO_V2_LINE_FLAG_OUTPUT)
> +               set_bit(FLAG_IS_OUT, flagsp);
> +       else if (flags & GPIO_V2_LINE_FLAG_INPUT)
> +               clear_bit(FLAG_IS_OUT, flagsp);
> +       assign_bit(FLAG_OPEN_DRAIN, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_OPEN_DRAIN);
> +       assign_bit(FLAG_OPEN_SOURCE, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_OPEN_SOURCE);
> +       assign_bit(FLAG_PULL_UP, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_BIAS_PULL_UP);
> +       assign_bit(FLAG_PULL_DOWN, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN);
> +       assign_bit(FLAG_BIAS_DISABLE, flagsp,
> +                  flags & GPIO_V2_LINE_FLAG_BIAS_DISABLED);
> +}
> +
> +static long line_get_values(struct line *line, void __user *ip)
> +{
> +       struct gpio_v2_line_values lv;
> +       DECLARE_BITMAP(vals, GPIO_V2_LINES_MAX);
> +       struct gpio_desc **descs;
> +       int ret, i, didx, num_get = 0;
> +
> +       /* NOTE: It's ok to read values of output lines. */
> +       if (copy_from_user(&lv, ip, sizeof(lv)))
> +               return -EFAULT;
> +
> +       if (lv.mask == 0)
> +               return -EINVAL;
> +
> +       for (i = 0; i < line->num_descs; i++)
> +               if (lv.mask & BIT_ULL(i))
> +                       num_get++;
> +       if (num_get == line->num_descs) {
> +               descs = line->descs;
> +       } else {
> +               descs = kmalloc_array(num_get, sizeof(*descs), GFP_KERNEL);
> +               for (didx = 0, i = 0; i < line->num_descs; i++) {
> +                       if (lv.mask & BIT_ULL(i)) {
> +                               descs[didx] = line->descs[i];
> +                               didx++;
> +                       }
> +               }
> +       }
> +       ret = gpiod_get_array_value_complex(false,
> +                                           true,
> +                                           num_get,
> +                                           descs,
> +                                           NULL,
> +                                           vals);
> +
> +       if (descs != line->descs)
> +               kfree(descs);
> +       if (ret)
> +               return ret;
> +
> +       lv.bits = 0;
> +       for (didx = 0, i = 0; i < line->num_descs; i++) {
> +               if (lv.mask & BIT_ULL(i)) {
> +                       if (test_bit(didx, vals))
> +                               lv.bits |= BIT_ULL(i);
> +                       didx++;
> +               }
> +       }
> +
> +       if (copy_to_user(ip, &lv, sizeof(lv)))
> +               return -EFAULT;
> +
> +       return 0;
> +}
> +
> +static long line_ioctl(struct file *file, unsigned int cmd,
> +                      unsigned long arg)
> +{
> +       struct line *line = file->private_data;
> +       void __user *ip = (void __user *)arg;
> +
> +       if (cmd == GPIO_V2_LINE_GET_VALUES_IOCTL)
> +               return line_get_values(line, ip);
> +
> +       return -EINVAL;
> +}
> +
> +#ifdef CONFIG_COMPAT
> +static long line_ioctl_compat(struct file *file, unsigned int cmd,
> +                             unsigned long arg)
> +{
> +       return line_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
> +}
> +#endif
> +
> +static void line_free(struct line *line)
> +{
> +       int i;
> +
> +       for (i = 0; i < line->num_descs; i++) {
> +               if (line->descs[i])
> +                       gpiod_free(line->descs[i]);
> +       }
> +       kfree(line->label);
> +       put_device(&line->gdev->dev);
> +       kfree(line);
> +}
> +
> +static int line_release(struct inode *inode, struct file *file)
> +{
> +       struct line *line = file->private_data;
> +
> +       line_free(line);
> +       return 0;
> +}
> +
> +static const struct file_operations line_fileops = {
> +       .release = line_release,
> +       .owner = THIS_MODULE,
> +       .llseek = noop_llseek,
> +       .unlocked_ioctl = line_ioctl,
> +#ifdef CONFIG_COMPAT
> +       .compat_ioctl = line_ioctl_compat,
> +#endif
> +};
> +
> +static int line_create(struct gpio_device *gdev, void __user *ip)
> +{
> +       struct gpio_v2_line_request lr;
> +       struct line *line;
> +       struct file *file;
> +       int fd, i, ret;
> +       struct gpio_v2_line_config *lc;
> +       unsigned long flags;
> +
> +       if (copy_from_user(&lr, ip, sizeof(lr)))
> +               return -EFAULT;
> +       if ((lr.num_lines == 0) || (lr.num_lines > GPIO_V2_LINES_MAX))
> +               return -EINVAL;
> +
> +       if (memchr_inv(lr.padding, 0, sizeof(lr.padding)))
> +               return -EINVAL;
> +
> +       lc = &lr.config;
> +       ret = gpio_v2_line_config_validate(lc, lr.num_lines);
> +       if (ret)
> +               return ret;
> +
> +       line = kzalloc(struct_size(line, descs, lr.num_lines),
> +                      GFP_KERNEL);
> +       if (!line)
> +               return -ENOMEM;
> +
> +       line->gdev = gdev;
> +       get_device(&gdev->dev);
> +
> +       /* Make sure this is terminated */
> +       lr.consumer[sizeof(lr.consumer)-1] = '\0';
> +       if (strlen(lr.consumer)) {
> +               line->label = kstrdup(lr.consumer, GFP_KERNEL);
> +               if (!line->label) {
> +                       ret = -ENOMEM;
> +                       goto out_free_line;
> +               }
> +       }
> +
> +       line->num_descs = lr.num_lines;
> +
> +       /* Request each GPIO */
> +       for (i = 0; i < lr.num_lines; i++) {
> +               u32 offset = lr.offsets[i];
> +               struct gpio_desc *desc = gpiochip_get_desc(gdev->chip, offset);
> +
> +               if (IS_ERR(desc)) {
> +                       ret = PTR_ERR(desc);
> +                       goto out_free_line;
> +               }
> +
> +               ret = gpiod_request(desc, line->label);
> +               if (ret)
> +                       goto out_free_line;
> +
> +               line->descs[i] = desc;
> +               flags = gpio_v2_line_config_flags(lc, i);
> +               gpio_v2_line_config_flags_to_desc_flags(flags, &desc->flags);
> +
> +               ret = gpiod_set_transitory(desc, false);
> +               if (ret < 0)
> +                       goto out_free_line;
> +
> +               /*
> +                * Lines have to be requested explicitly for input
> +                * or output, else the line will be treated "as is".
> +                */
> +               if (flags & GPIO_V2_LINE_FLAG_OUTPUT) {
> +                       int val = gpio_v2_line_config_output_value(lc, i);
> +
> +                       ret = gpiod_direction_output(desc, val);
> +                       if (ret)
> +                               goto out_free_line;
> +               } else if (flags & GPIO_V2_LINE_FLAG_INPUT) {
> +                       ret = gpiod_direction_input(desc);
> +                       if (ret)
> +                               goto out_free_line;
> +               }
> +
> +               blocking_notifier_call_chain(&desc->gdev->notifier,
> +                                            GPIOLINE_CHANGED_REQUESTED, desc);
> +
> +               dev_dbg(&gdev->dev, "registered chardev handle for line %d\n",
> +                       offset);
> +       }
> +
> +       fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
> +       if (fd < 0) {
> +               ret = fd;
> +               goto out_free_line;
> +       }
> +
> +       file = anon_inode_getfile("gpio-line",
> +                                 &line_fileops,
> +                                 line,
> +                                 O_RDONLY | O_CLOEXEC);
> +       if (IS_ERR(file)) {
> +               ret = PTR_ERR(file);
> +               goto out_put_unused_fd;
> +       }
> +
> +       lr.fd = fd;
> +       if (copy_to_user(ip, &lr, sizeof(lr))) {
> +               /*
> +                * fput() will trigger the release() callback, so do not go onto
> +                * the regular error cleanup path here.
> +                */
> +               fput(file);
> +               put_unused_fd(fd);
> +               return -EFAULT;
> +       }
> +
> +       fd_install(fd, file);
> +
> +       dev_dbg(&gdev->dev, "registered chardev handle for %d lines\n",
> +               line->num_descs);
> +
> +       return 0;
> +
> +out_put_unused_fd:
> +       put_unused_fd(fd);
> +out_free_line:
> +       line_free(line);
> +       return ret;
> +}
> +
> +#ifdef CONFIG_GPIO_CDEV_V1
>
>  /*
>   * GPIO line event management
> @@ -745,6 +1132,8 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
>         return ret;
>  }
>
> +#endif /* CONFIG_GPIO_CDEV_V1 */
> +
>  static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
>                                   struct gpioline_info *info)
>  {
> @@ -842,6 +1231,7 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>                 if (copy_to_user(ip, &chipinfo, sizeof(chipinfo)))
>                         return -EFAULT;
>                 return 0;
> +#ifdef CONFIG_GPIO_CDEV_V1
>         } else if (cmd == GPIO_GET_LINEINFO_IOCTL) {
>                 struct gpioline_info lineinfo;
>
> @@ -884,6 +1274,9 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>                 }
>
>                 return 0;
> +#endif /* CONFIG_GPIO_CDEV_V1 */
> +       } else if (cmd == GPIO_V2_GET_LINE_IOCTL) {
> +               return line_create(gdev, ip);
>         } else if (cmd == GPIO_GET_LINEINFO_UNWATCH_IOCTL) {
>                 if (copy_from_user(&offset, ip, sizeof(offset)))
>                         return -EFAULT;
> @@ -1109,4 +1502,24 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
>  void gpiolib_cdev_unregister(struct gpio_device *gdev)
>  {
>         cdev_device_del(&gdev->chrdev, &gdev->dev);
> +
> +       /*
> +        * array sizes must ensure 64-bit alignment and not create holes in
> +        * the struct packing.
> +        */
> +       BUILD_BUG_ON(GPIO_V2_LINES_MAX % 2);
> +       BUILD_BUG_ON(GPIO_MAX_NAME_SIZE % 8);
> +
> +       /*
> +        * check that uAPI structs are 64-bit aligned for 32/64-bit
> +        * compatibility
> +        */
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_attribute) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_config_attribute) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_config) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_request) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_info) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_info_changed) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_event) % 8);
> +       BUILD_BUG_ON(sizeof(struct gpio_v2_line_values) % 8);

You can use IS_ALIGNED() within BUILD_BUG_ON() for these checks and
I'd also put them somewhere else than the unregister function. Maybe
move it over to cdev_register() so that they're more visible?

>  }
> --
> 2.28.0
>

Bart

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