linux-kernel - Re: [PATCH 1/2] pinctrl: core: configure pinmux from pins debug file

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Date:   Tue, 18 May 2021 15:57:42 +0200 (CEST)
From:   Dario Binacchi <dariobin@...ero.it>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Drew Fustini <drew@...gleboard.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 1/2] pinctrl: core: configure pinmux from pins debug
 file

Hi,

> Il 17/05/2021 22:02 Andy Shevchenko <andy.shevchenko@...il.com> ha scritto:
> 
>  
> On Sun, May 16, 2021 at 7:43 PM Dario Binacchi <dariobin@...ero.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() ?

Ok, I'll use strncpy_from_user() in the next version of the patch

> 
> 
> > +       token = strsep(&c, " ");
> 
> > +       if (kstrtouint(token, 0, &pin))
> > +               return -EINVAL;
> 
> Don't shadow an error code.

You are right

> 
> > +       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?

I want to make sure the pin is managed

Thanks and regards,
Dario
> 
> > +               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