linux-kernel - Re: [PATCH v3] reset: add support for non-DT systems

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Date:   Mon, 19 Feb 2018 14:13:27 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     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 v3] reset: add support for non-DT systems

Hi Bartosz,

On Mon, 2018-02-19 at 13:34 +0100, Bartosz Golaszewski 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, an additional, optional identifier
> string and the reset id number.
> 
> 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[] = {
> 	{ .dev = "foo",   .reset_id = "foo_id",    .id = 14 },
> 	{ .dev = "bar",   .id = NULL,              .id = 3  },
> 	{ }
> };

Thank you for the patch. This is a useful addition, but the lookups
should be added in platform code, not by the reset controller driver.

I would prefer reset_lookups to follow the patterns set by the other
subsystem's lookup implementations:
clk, gpiod, phy, and pwm have lookups that can be created from platform
code, independently from the drivers (via clkdev_add_table,
gpiod_add_lookup_table, phy_create_lookup, and pwm_add_table).

Following this pattern would allow to support reset controllers that are
implemented as proper device drivers, and reset controllers that are
reused on multiple platforms.

regards
Philipp