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

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Date:   Mon, 28 Jan 2019 14:51:12 +0200
From:   Vladimir Zapolskiy <vz@...ia.com>
To:     Linus Walleij <linus.walleij@...aro.org>
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

Hi Linus,

On 01/28/2019 02:36 PM, Linus Walleij wrote:
> 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.)
> 

Fortunately it has been already done, please check the sent v2 with one
earned Reviewed-by tag from Richard:

* https://patchwork.ozlabs.org/patch/1029536/
* https://patchwork.ozlabs.org/patch/1029537/

Thank you for your approval of the change in general!

--
Best wishes,
Vladimir