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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Mon, 17 May 2021 23:02:00 +0300
Message-ID: <CAHp75Vd8875hRNk1JK6gkmfxjqxBSu4cRNE1zJt9TyEW7TvsMg@mail.gmail.com>
Subject: Re: [PATCH 1/2] pinctrl: core: configure pinmux from pins debug file
To:     Dario Binacchi <dariobin@libero.it>,
        Drew Fustini <drew@beagleboard.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>
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On Sun, May 16, 2021 at 7:43 PM Dario Binacchi <dariobin@libero.it> wrote:
>
> The MPUs of some architectures (e.g AM335x) must be in privileged
> operating mode to write on the pinmux

pinmux is not pin configuration. You need to rethink the approach.

> registers. In such cases, where
> writes will not work from user space, now it can be done from the pins
> debug file if the platform driver exports the pin_dbg_set() helper among
> the registered operations.

Drew, is it similar to what you are trying to achieve?

...

> +static ssize_t pinctrl_pins_write(struct file *file,
> +                                 const char __user *user_buf, size_t count,
> +                                 loff_t *ppos)
> +{
> +       struct seq_file *s = file->private_data;
> +       struct pinctrl_dev *pctldev = s->private;
> +       const struct pinctrl_ops *ops = pctldev->desc->pctlops;
> +       char buf[32];
> +       char *c = &buf[0];
> +       char *token;
> +       int ret, buf_size;
> +       unsigned int i, pin;
> +
> +       if (!ops->pin_dbg_set)
> +               return -EFAULT;
> +
> +       /* Get userspace string and assure termination */
> +       buf_size = min(count, sizeof(buf) - 1);
> +       if (copy_from_user(buf, user_buf, buf_size))
> +               return -EFAULT;
> +
> +       buf[buf_size] = 0;

Can't you use strncpy_from_user() ?


> +       token = strsep(&c, " ");

> +       if (kstrtouint(token, 0, &pin))
> +               return -EINVAL;

Don't shadow an error code.

> +       for (i = 0; i < pctldev->desc->npins; i++) {
> +               if (pin != pctldev->desc->pins[i].number)
> +                       continue;

Hmm... I don't get this. Why is it needed?

> +               ret = ops->pin_dbg_set(pctldev, pin, c);
> +               if (ret)
> +                       return ret;
> +
> +               return count;
> +       }
> +
> +       return -EINVAL;
> +}

...

> -       debugfs_create_file("pins", 0444,
> +       debugfs_create_file("pins", 0644,
>                             device_root, pctldev, &pinctrl_pins_fops);

Why is it in this file?


-- 
With Best Regards,
Andy Shevchenko