linux-kernel - Re: [PATCH] Input: cyttsp5 - ensure minimum reset pulse width

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Message-Id: <20250205105057.3ec9fe8c8935c3a72061edad@hugovil.com>
Date: Wed, 5 Feb 2025 10:50:57 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Alistair Francis
 <alistair@...stair23.me>, Maxime Ripard <mripard@...nel.org>,
 Mylène Josserand <mylene.josserand@...tlin.com>, Hugo
 Villeneuve <hvilleneuve@...onoff.com>, stable@...r.kernel.org,
 linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: cyttsp5 - ensure minimum reset pulse width

On Wed, 5 Feb 2025 07:33:36 -0800
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:

> On Tue, Feb 04, 2025 at 02:01:00PM -0500, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > 
> > The current reset pulse width is measured to be 5us on a
> > Renesas RZ/G2L SOM. The manufacturer's minimum reset pulse width is
> > specified as 10us.
> > 
> > Extend reset pulse width to make sure it is long enough on all platforms.
> > 
> > Also reword confusing comments about reset pin assertion.
> > 
> > Fixes: 5b0c03e24a06 ("Input: Add driver for Cypress Generation 5 touchscreen")
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > ---
> >  drivers/input/touchscreen/cyttsp5.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/input/touchscreen/cyttsp5.c b/drivers/input/touchscreen/cyttsp5.c
> > index eafe5a9b8964..bb09e84d0e92 100644
> > --- a/drivers/input/touchscreen/cyttsp5.c
> > +++ b/drivers/input/touchscreen/cyttsp5.c
> > @@ -870,13 +870,16 @@ static int cyttsp5_probe(struct device *dev, struct regmap *regmap, int irq,
> >  	ts->input->phys = ts->phys;
> >  	input_set_drvdata(ts->input, ts);
> >  
> > -	/* Reset the gpio to be in a reset state */
> > +	/* Assert gpio to be in a reset state */
> >  	ts->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> >  	if (IS_ERR(ts->reset_gpio)) {
> >  		error = PTR_ERR(ts->reset_gpio);
> >  		dev_err(dev, "Failed to request reset gpio, error %d\n", error);
> >  		return error;
> >  	}
> > +
> > +	fsleep(1000); /* Ensure long-enough reset pulse (minimum 10us). */
> > +
> 
> If the manufacturer specified that 10us is enough why do we want to wait
> 100 times longer?

Hi,
10us would do fine. I simply put 1ms because it is then much easier to
see the reset pulse on an oscilloscope when correlating it
with other signals.

Hugo.


-- 
Hugo Villeneuve