linux-kernel - Re: [PATCH v2] reset: add support for non-DT systems

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Date:   Wed, 14 Feb 2018 09:59:53 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...libre.com>,
        David Lechner <david@...hnology.com>
Subject: Re: [PATCH v2] reset: add support for non-DT systems

2018-02-13 20:17 GMT+01:00 Andy Shevchenko <andy.shevchenko@...il.com>:
> On Tue, Feb 13, 2018 at 8:39 PM, Bartosz Golaszewski <brgl@...ev.pl> wrote:
>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>
>> The reset framework only supports device-tree. There are some platforms
>> however, which need to use it even in legacy, board-file based mode.
>>
>> An example of such architecture is the DaVinci family of SoCs which
>> supports both device tree and legacy boot modes and we don't want to
>> introduce any regressions.
>>
>> We're currently working on converting the platform from its hand-crafted
>> clock API to using the common clock framework. Part of the overhaul will
>> be representing the chip's power sleep controller's reset lines using
>> the reset framework.
>>
>> This changeset extends the core reset code with a new field in the
>> reset controller struct which contains an array of lookup entries. Each
>> entry contains the device name and an additional, optional identifier
>> string.
>>
>> Drivers can register a set of reset lines using this lookup table and
>> concerned devices can access them using the regular reset_control API.
>>
>> This new function is only called as a fallback in case the of_node
>> field is NULL and doesn't change anything for current users.
>>
>> Tested with a dummy reset driver with several lookup entries.
>>
>> An example lookup table can look like this:
>>
>> static const struct reset_lookup foobar_reset_lookup[] = {
>>         [FOO_RESET] = { .dev = "foo", .id = "foo_id" },
>>         [BAR_RESET] = { .dev = "bar", .id = NULL },
>>         { }
>> };
>>
>> where FOO_RESET and BAR_RESET will correspond with the id parameters
>> of reset callbacks.
>
>> +static struct reset_control *
>> +__reset_control_get_from_lookup(struct device *dev, const char *id,
>> +                               bool shared, bool optional)
>> +{
>> +       struct reset_controller_dev *rcdev;
>> +       const char *dev_id = dev_name(dev);
>> +       struct reset_control *rstc = NULL;
>> +       const struct reset_lookup *lookup;
>> +       int index;
>> +
>> +       mutex_lock(&reset_list_mutex);
>> +
>> +       list_for_each_entry(rcdev, &reset_controller_list, list) {
>> +               if (!rcdev->lookup)
>> +                       continue;
>> +
>> +               lookup = rcdev->lookup;
>
>> +               for (index = 0; lookup->dev; index++, lookup++) {
>> +                       if (strcmp(dev_id, lookup->dev))
>> +                               continue;
>> +
>> +                       if ((!id && !lookup->id) ||
>> +                           (id && lookup->id && !strcmp(id, lookup->id))) {
>> +                               rstc = __reset_control_get_internal(rcdev,
>> +                                                               index, shared);
>> +                               break;
>> +                       }
>
> Wouldn't be slightly more readable
>
>       if (id && lookup->id) {
>         if (strcmp(id, lookup->id))
>           continue;
>       } else if (id || lookup->id) {
>         continue;
>       }
>
>       rstc = __reset_control_get_internal(rcdev, index, shared);
>       break;
>

You'd get less indentations, yes but I wanted to emphasize the
condition on which we want to stop in this line.

>> +               }
>> +       }
>> +
>> +       mutex_unlock(&reset_list_mutex);
>> +
>
>> +       if (!rstc)
>> +               return optional ? NULL : ERR_PTR(-ENOENT);
>
> Isn't simpler
>
> if (!optional && !rstc) // or other way around, depending which might
> be more offten
>  return ERR_PTR(...);
>

IMO it's just a matter of taste.

Thanks,
Bartosz