linux-kernel - Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on Intel Baytrail

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:	Mon, 13 Oct 2014 14:26:32 -0500
From:	Felipe Balbi <balbi@...com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
CC:	Felipe Balbi <balbi@...com>, <linus.walleij@...aro.org>,
	<linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on
 Intel Baytrail

Hi,

On Mon, Oct 13, 2014 at 12:24:04PM -0700, David Cohen wrote:
> On Mon, Oct 13, 2014 at 02:14:05PM -0500, Felipe Balbi wrote:
> > On Mon, Oct 13, 2014 at 11:23:59AM -0700, David Cohen wrote:
> > > Even if a gpio pin is set to output, we still need to set INPUT_EN bit
> > 
> > here you say you're setting that bit.
> > 
> > > to be able to read its value. Without this change, we'll always read low
> > > level state.
> > > 
> > > Cc: <stable@...r.kernel.org> # v3.14+
> > > Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> > > ---
> > > 
> > > Hi,
> > > 
> > > I'm resending same v1 patch but now copying linux stable and linux gpio.
> > > This patch is meant for all linux stable trees >= v3.14.
> > > 
> > > Br, David
> > > ---
> > > 
> > >  drivers/pinctrl/pinctrl-baytrail.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pinctrl/pinctrl-baytrail.c b/drivers/pinctrl/pinctrl-baytrail.c
> > > index e12e5b07f6d7..c23d8ded936d 100644
> > > --- a/drivers/pinctrl/pinctrl-baytrail.c
> > > +++ b/drivers/pinctrl/pinctrl-baytrail.c
> > > @@ -318,7 +318,7 @@ static int byt_gpio_direction_output(struct gpio_chip *chip,
> > >  		"Potential Error: Setting GPIO with direct_irq_en to output");
> > >  
> > >  	reg_val = readl(reg) | BYT_DIR_MASK;
> > > -	reg_val &= ~BYT_OUTPUT_EN;
> > > +	reg_val &= ~(BYT_OUTPUT_EN | BYT_INPUT_EN);
> > 
> > but code is clearing it. Also, you're not patching byt_gpio_get(), so
> > you can't be 'reading its value' either. Quite frankly, this looks very
> > fishy to me. Comments on BYT_OUTPUT_EN and BYT_INPUT_EN states that
> > those bits are active low, meaning that clearing them enables that
> > particular feature.
> > 
> > How can you enable a pin to be both OUTPUT and INPUT ? Look like what
> > you really want is:
> > 
> > diff --git a/drivers/pinctrl/pinctrl-baytrail.c b/drivers/pinctrl/pinctrl-baytrail.c
> > index e12e5b0..69f882d 100644
> > --- a/drivers/pinctrl/pinctrl-baytrail.c
> > +++ b/drivers/pinctrl/pinctrl-baytrail.c
> > @@ -290,6 +290,7 @@ static int byt_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
> >  
> >  	value = readl(reg) | BYT_DIR_MASK;
> >  	value &= ~BYT_INPUT_EN;		/* active low */
> > +	value |= BYT_OUTPUT_EN;		/* disable output */
> >  	writel(value, reg);
> >  
> >  	spin_unlock_irqrestore(&vg->lock, flags);
> > @@ -319,6 +320,7 @@ static int byt_gpio_direction_output(struct gpio_chip *chip,
> >  
> >  	reg_val = readl(reg) | BYT_DIR_MASK;
> >  	reg_val &= ~BYT_OUTPUT_EN;
> > +	value |= BYT_INPUT_EN;		/* disable input */
> >  
> >  	if (value)
> >  		writel(reg_val | BYT_LEVEL, reg);
> > 
> > completely untested however. Care to further explain why clearing both
> > bits - thus enabling both INPUT and OUTPUT - is correct ?
> 
> Actually I really meant what I sent, but perhaps I misspoke during
> explanation. We need to clear the bit to enable the functionality.
> 
> !BYT_INPUT_EN allows us to read the value. !BYT_OUTPUT_EN allows us to
> set a value. If we want to set a value (acting as output) and still be
> able to read via sysfs, we need to set both functionality (i.e. clear
> both bits).
> 
> I'll resend the patch with a better comment.

Alright, just make sure that exposing a pin through sysfs and making it
output high, then later switching it to input works. It looks like
byt_gpio_direction_input() still needs to make sure OUTPUT is set.

-- 
balbi

Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)