linux-kernel - Re: [PATCH v4] clk: Add write operation for clk

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Date:   Thu, 7 Oct 2021 17:39:18 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Mike Tipton <mdtipton@...eaurora.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andy Shevchenko <andy@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] clk: Add write operation for clk_parent debugfs node

On Thu, Oct 7, 2021 at 5:09 PM Sam Protsenko <semen.protsenko@...aro.org> wrote:
>
> Useful for testing mux clocks. One can write the index of the parent to
> be set into clk_parent node, starting from 0. Example
>
>     # cd /sys/kernel/debug/clk/mout_peri_bus
>     # cat clk_possible_parrents
>       dout_shared0_div4 dout_shared1_div4
>     # cat clk_parent
>       dout_shared0_div4
>     # echo 1 > clk_parent
>     # cat clk_parent
>       dout_shared1_div4
>
> CLOCK_ALLOW_WRITE_DEBUGFS has to be defined in drivers/clk/clk.c in
> order to use this feature.

...

> +static ssize_t current_parent_write(struct file *file, const char __user *ubuf,
> +                                   size_t count, loff_t *ppos)
> +{
> +       struct seq_file *s = file->private_data;
> +       struct clk_core *core = s->private;
> +       struct clk_core *parent;

> +       char buf[4] = { 0 };

We may use {} (in a more standardized way), but see below.

> +       u8 idx;
> +       int err;

> +       if (copy_from_user(&buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
> +               return -EFAULT;
> +
> +       err = kstrtou8(buf, 0, &idx);
> +       if (err)
> +               return err;

NIH kstrotu8_from_user().

> +       parent = clk_core_get_parent_by_index(core, idx);
> +       if (!parent)
> +               return -ENOENT;
> +
> +       clk_prepare_lock();
> +       err = clk_core_set_parent_nolock(core, parent);
> +       clk_prepare_unlock();
> +       if (err)
> +               return err;
> +
> +       return count;
> +}

...

> +#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
> +               if (core->num_parents > 1) {
> +                       debugfs_create_file("clk_parent", 0644, root, core,
> +                                           &current_parent_rw_fops);

> +               } else {
> +                       debugfs_create_file("clk_parent", 0444, root, core,
> +                                           &current_parent_fops);
> +               }
> +#else
>                 debugfs_create_file("clk_parent", 0444, root, core,
>                                     &current_parent_fops);

Dup. You can avoid it.

> +#endif
> +       }

-- 
With Best Regards,
Andy Shevchenko