linux-kernel - Re: [PATCH] pinctrl: remove unused 'pinconf-config' debugfs interface

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Message-ID: <CACRpkdYn+LgeRaL4=UPLGYxdCpnoj8r3Yp=A6yHADr=fhB_UFg@mail.gmail.com>
Date:   Mon, 28 Jan 2019 13:36:59 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Vladimir Zapolskiy <vz@...ia.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Laurent Meunier <laurent.meunier@...com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] pinctrl: remove unused 'pinconf-config' debugfs interface

On Sun, Jan 20, 2019 at 4:14 PM Vladimir Zapolskiy <vz@...ia.com> wrote:

> The main goal of the change is to remove .pin_config_dbg_parse_modify
> callback before a driver with its support appears. So far the in-kernel
> interface did not attract any users since its introduction 5 years ago.
>
> Originally .pin_config_dbg_parse_modify callback and the associated
> 'pinconf-config' debugfs file were introduced in commit f07512e615dd
> ("pinctrl/pinconfig: add debug interface"), a short description of
> 'pinconf-config' usage for debugging can be expressed this way:
>
> Write to 'pinconf-config' (see pinconf_dbg_config_write() function):
>
> % echo -n modify $map_type $device_name $state_name $pin_name $config > \
>         /sys/kernel/debug/pinctrl/$pinctrl/pinconf-config
>
> It supposes to update a global (therefore single!) 'pinconf_dbg_conf'
> variable with an alternative setting, the arguments should match
> an existing pinconf device and some registered pinctrl mapping 'map':
>
> * $map_type is either 'config_pin' or 'config_group', it should match
>   'map->type' value of PIN_MAP_TYPE_CONFIGS_PIN or
>    PIN_MAP_TYPE_CONFIGS_GROUP accordingly,
> * $device_name should match 'map->dev_name' string value,
> * $state_name should match 'map->name' string value,
> * $pin_name should match 'map->data.configs.group_or_pin' string value,
>
> If all above has matched, then $config is a new value to be set by calling
> pinconfops->pin_config_dbg_parse_modify(pctldev, config, matched_config).
>
> After a successful write into 'pinconf-config' a user can read the file
> to get information about that single modified pin configuration.
>
> The fact is .pin_config_dbg_parse_modify callback has never been defined
> in 'struct pinconf_ops' of any pinconf driver, thus an actual modification
> of a pin or group state on any present pinconf controller does not happen,
> and it declares that all related code is no more than dead code.
>
> I discovered the issue while attempting to add .pin_config_dbg_parse_modify
> support in some drivers and found that too short 'MAX_NAME_LEN' set by
>
>   drivers/pinctrl/pinconf.c:372:#define MAX_NAME_LEN 15
>
> is practically insufficient to store a regular pinctrl device name,
> which are like 'e6060000.pin-controller-sh-pfc' or pin names like
> 'MX6QDL_PAD_ENET_REF_CLK', thus it is another indicator that the code
> is barely usable, insufficiently tested and unprepossessing.
>
> Of course it might be possible to increase MAX_NAME_LEN, and then add
> .pin_config_dbg_parse_modify callbacks to the drivers, but the whole
> idea of such a limited debug option looks inviable. A more flexible
> way to functionally substitute the original approach is to implicitly
> or explicitly use pinctrl_select_state() function whenever needed.
>
> Signed-off-by: Vladimir Zapolskiy <vz@...ia.com>
> Cc: Laurent Meunier <laurent.meunier@...com>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Russell King <linux@....linux.org.uk>

This is fine, the build robot is complaining of some missing
prototype though, probably some implicit include that
disappeared when you removed <linux/pinctrl/machine.h>
from the <linux/pinctrl/pinconf.h> file.

Will you send a v2 with this fixed? (I think just leaving the
include in place would be a quickfix.)

Yours,
Linus Walleij