From: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
To: Nick Dyer <nick@shmanahar.org>
Cc: Ezequiel Garcia <ezequiel@collabora.com>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel@collabora.com
Subject: Re: [PATCH] Input: atmel_mxt_ts - fix reset-gpio for level based irqs
Date: Mon, 23 Apr 2018 13:43:35 +0200 [thread overview]
Message-ID: <20180423114335.n5n7q4arn2petcnd@earth.universe> (raw)
In-Reply-To: <20180421201137.fyr6eqzjuob765ie@hairyalien>
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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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next prev parent reply other threads:[~2018-04-23 11:43 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-20 17:24 [PATCH] Input: atmel_mxt_ts - fix reset-gpio for level based irqs Sebastian Reichel
2018-04-20 17:44 ` Ezequiel Garcia
2018-04-20 19:42 ` Sebastian Reichel
2018-04-21 20:11 ` Nick Dyer
2018-04-23 11:43 ` Sebastian Reichel [this message]
2018-04-23 11:58 ` [PATCHv2] " Sebastian Reichel
2018-05-03 9:15 ` Sebastian Reichel
2018-05-09 14:25 ` Pavel Machek
2018-05-09 14:40 ` Sebastian Reichel
2018-05-24 16:35 ` Dmitry Torokhov
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