linux-kernel - Re: [PATCH] Input: atmel_mxt_ts - fix reset-gpio for level based irqs

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Date:   Fri, 20 Apr 2018 21:42:07 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     Nick Dyer <nick@...anahar.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH] Input: atmel_mxt_ts - fix reset-gpio for level based irqs

On Fri, Apr 20, 2018 at 02:44:02PM -0300, Ezequiel Garcia wrote:
> Hi Sebastian,
> 
> On Fri, 2018-04-20 at 19:24 +0200, Sebastian Reichel wrote:
> > The current reset-gpio support triggers an interrupt storm on platforms
> > using the maxtouch with level based interrupt. The Motorola Droid 4,
> > which I used for some of the tests is not affected, since it uses a level
> > based interrupt.
> > 
> 
> I found this confusing. Interrupt storm happen with level-based interrupts,
> but the Droid4 is not affected?

This is a typo. Droid 4 has an edge based interrupt defined, PPD has
an level based interrupt defined. PPD got an interrupt storm, Droid 4
did not.

> > This change avoids the interrupt storm by enabling the device while
> > its interrupt is disabled. The following mxt_initialize() requires,
> > that the device is responsive (at least mxt224E is unresponsive for
> > ~22ms), so we wait some time. We don't wait for leaving bootloader
> > mode anymore, since mxt_initialize() checks for it anyways.
> > 
> 
> IMHO, having some more or less arbritrary sleeps is almost
> always a problem. This value might be enough for some platform,
> might be too short for some other, and then it might get too large
> for someone else.

The 22ms chip-being-unresponsive are not newly introduced. The
same 22ms are also required for soft-reset. I did introduce a
new time (MXT_RESET_GPIO_TIME) for the "chip being reset" state,
since my randomly chosen 200ms from before were exaggerated
considering all mxt datasheets I checked stated only a few nano
seconds.

> > This fixes a boot problem on GE PPD (watchdog kills device) and also
> > has been tested on the Droid 4.
> > 
> > Fixes: f657b00df22e ("Input: atmel_mxt_ts - add support for reset line")
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> > ---
> >  drivers/input/touchscreen/atmel_mxt_ts.c | 15 +++++----------
> >  1 file changed, 5 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> > index 5d9699fe1b55..f8a9f2a47e78 100644
> > --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> > +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> > @@ -194,6 +194,7 @@ enum t100_type {
> >  
> >  /* Delay times */
> >  #define MXT_BACKUP_TIME		50	/* msec */
> > +#define MXT_RESET_GPIO_TIME	20	/* msec */
> >  #define MXT_RESET_TIME		200	/* msec */
> >  #define MXT_RESET_TIMEOUT	3000	/* msec */
> >  #define MXT_CRC_TIMEOUT		1000	/* msec */
> > @@ -3167,20 +3168,14 @@ static int mxt_probe(struct i2c_client *client, const struct i2c_device_id *id)
> >  		return error;
> >  	}
> >  
> > +	disable_irq(client->irq);
> > +
> >  	if (data->reset_gpio) {
> > -		data->in_bootloader = true;
> > -		msleep(MXT_RESET_TIME);
> > -		reinit_completion(&data->bl_completion);
> > +		msleep(MXT_RESET_GPIO_TIME);
> >  		gpiod_set_value(data->reset_gpio, 1);
> 
> Can't we enable the IRQ here, just before the wait...
> 
> > -		error = mxt_wait_for_completion(data, &data->bl_completion,
> > -						MXT_RESET_TIMEOUT);
> 
> ... and then disable it back afterwards?

Yes and no. We need the wait, since the interrupt pin does random
stuff for 100ms after reset. We can do the wait-for-completion
after that time (see mxt_soft_reset function). I kept it simple,
since the following init does another soft reset anyways.

> > -		if (error)
> > -			return error;
> > -		data->in_bootloader = false;
> > +		msleep(MXT_RESET_TIME);
> 
> >  	}
> >  
> > -	disable_irq(client->irq);
> > -
> >  	error = mxt_initialize(data);
> >  	if (error)
> >  		return error;

-- Sebastian

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