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

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Message-ID: <20180423114335.n5n7q4arn2petcnd@earth.universe>
Date:   Mon, 23 Apr 2018 13:43:35 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Nick Dyer <nick@...anahar.org>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        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

Hi,

On Sat, Apr 21, 2018 at 09:11:37PM +0100, Nick Dyer wrote:
> On Fri, Apr 20, 2018 at 09:42:07PM +0200, Sebastian Reichel wrote:
> > 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?
> 
> Can I ask what happens during the interrupt storm. Are you getting lots
> of the "failed to read T44 and T5" message, or something else?

I don't get any message (with DEBUG enabled for the driver).
The boot process hangs and after a few seconds the watchdog kicks in.

> > > > 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.
> 
> According to the data sheets there is a period after a reset where the
> CHG line is temporarily set as an input, during which the host should
> ignore it. If you don't, you might get a stray interrupt and try and
> communicate with the device, which might leave it in a bad state. I
> think you mentioned that later in your email.
> 
> The reset time varies per chip, but the 100ms in mxt_soft_reset() was
> based on discussions with app support at Atmel, so should be correct in
> most cases.

Right. This sleep time is missing for the gpio based reset. The
other checks are not required, since the chip initialization
routine is called directly afterwards. I will send a PATCHv2,
that fixes the patch description and uses the same timeout value
for both resets.

-- Sebastian

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