From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kishon Vijay Abraham I Subject: Re: [PATCH] gpio: pcf857x: restore the initial line state of all pcf lines Date: Thu, 18 Dec 2014 11:48:17 +0530 Message-ID: <549271A9.5040701@ti.com> References: <1418371601-22658-1-git-send-email-kishon@ti.com> <548F498F.7050202@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: Received: from comal.ext.ti.com ([198.47.26.152]:36072 "EHLO comal.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751113AbaLRGSW (ORCPT ); Thu, 18 Dec 2014 01:18:22 -0500 In-Reply-To: <548F498F.7050202@ti.com> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Nishanth Menon , linus.walleij@linaro.org, gnurou@gmail.com, linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, nsekhar@ti.com Cc: linux-omap@vger.kernel.org, linux-mmc@vger.kernel.org, Benoit Parrot On Tuesday 16 December 2014 02:20 AM, Nishanth Menon wrote: > On 12/12/2014 02:06 AM, Kishon Vijay Abraham I wrote: >> The reset values for all the PCF lines are high and hence on shutdown >> we should drive all the lines high in order to bring it to the reset state. >> >> This is actually required since pcf doesn't have a reset line and even after >> warm reset (by invoking "reboot" in prompt) the pcf lines maintains it's >> previous programmed state. This becomes a problem if the boards are designed >> to work with the default initial state. >> >> DRA7XX_evm uses PCF8575 and one of the PCF output lines feeds to MMC/SD and >> this line should be driven high in order for the MMC/SD to be detected. >> This line is modelled as regulator and the hsmmc driver takes care of enabling >> and disabling it. In the case of 'reboot', during shutdown path as part of it's >> cleanup process the hsmmc driver disables this regulator. This makes MMC boot >> not functional. >> >> Fixed it by driving high all the pcf lines. >> >> Signed-off-by: Kishon Vijay Abraham I >> --- >> drivers/gpio/gpio-pcf857x.c | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/drivers/gpio/gpio-pcf857x.c b/drivers/gpio/gpio-pcf857x.c >> index 236708a..00b15b2 100644 >> --- a/drivers/gpio/gpio-pcf857x.c >> +++ b/drivers/gpio/gpio-pcf857x.c >> @@ -448,6 +448,14 @@ static int pcf857x_remove(struct i2c_client *client) >> return status; >> } >> >> +static void pcf857x_shutdown(struct i2c_client *client) >> +{ >> + struct pcf857x *gpio = i2c_get_clientdata(client); >> + >> + /* Drive all the I/O lines high */ >> + gpio->write(gpio->client, BIT(gpio->chip.ngpio) - 1); > > you might force a contention here - depending on System configuration. > example: > +-------+ > | | > | U1 | +------+ +-----------+ > | +---------> | | | > +-------+ | | | | > | Switch<-----+ SoC | > +-------+ | | | | > | | | | | | > | U2 <---------+--^---+ +-----------+ > | | | > | | | > +-------+ | > +--+--+ > | | > | PCF | > | | > +-----+ > > At low, SoC pin is connected to U2 as drive. when reset to high, you > now have U1 driving to the same pin that SoC has, potentially > resulting in contention. > > > Unfortunately, at this level, you do not know what the state of the > system is, blindly forcing a pin level will potentially cause > contention risk depending on pin configuration. Assume we are doing a reset when the system is powered on, irrespective of the state of the system, we'll be forcing the pin level to the default state. The same thing happens here so I don't think this would be a problem. Thanks Kishon