linux-kernel - Re: [PATCH] pinctrl: document the "GPIO mode" pitfall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 25 Apr 2013 23:39:18 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>,
	Pankaj Dev <pankaj.dev@...com>
Subject: Re: [PATCH] pinctrl: document the "GPIO mode" pitfall

On Tue, Apr 23, 2013 at 3:33 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:

>> +And your machine configuration may look like this:
>> +--------------------------------------------------
>> +
>> +static unsigned long uart_default_mode[] = {
>> +    PIN_CONF_PACKED(PIN_CONFIG_DRIVE_PUSH_PULL, 0),
>> +};
>> +
>> +static unsigned long uart_sleep_mode[] = {
>> +    PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0),
>> +};
>
> I'm having a bit of trouble with PIN_CONFIG_DRIVE_PUSH_PULL and
> PIN_CONFIG_OUTPUT. Strictly speaking, when configured in output mode, the pin
> will be in a push-pull configuration.

For your system or for any system? Open drain, open source are also
output modes, and none of them are push-pull.

> Could you clarify the exact scope of the
> two configuration parameters ?

PIN_CONFIG_OUTPUT is left a bit unspecified, but here the
idea was a passive drive, like just connecting the pin to
VDD or GND without any driver stage at all. Maybe I should
patch the documentation since we seem to be the only
user?

In the above case (which is derived from the ABx500) I think what is
happening is that the pin is connected to ground during sleep,
without any enabled driver stages, which saves a lot of power,
since you do not need to bias the totempole during
sleep in that way.

Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/