From: Lucas Stach <l.stach@pengutronix.de>
To: Angus Ainslie <angus@akkea.ca>
Cc: Fabio Estevam <festevam@gmail.com>,
cphealy@gmail.com, kernel@pengutronix.de, shawnguo@kernel.org,
linux-arm-kernel@lists.infradead.org, linux-imx@nxp.com
Subject: Re: [PATCH] arm64: dts: imx8mq-zii-ultra: Operate I2C at 100kHz
Date: Thu, 23 May 2019 17:01:53 +0200 [thread overview]
Message-ID: <1558623713.2624.54.camel@pengutronix.de> (raw)
In-Reply-To: <aea4106a575d0e623442c53cfd50917b@www.akkea.ca>
Am Donnerstag, den 23.05.2019, 06:19 -0700 schrieb Angus Ainslie:
> Hi Lucas
>
> On 2019-05-13 07:07, Lucas Stach wrote:
> > Hi Fabio,
> >
> > Am Montag, den 13.05.2019, 11:02 -0300 schrieb Fabio Estevam:
> > > According to the i.MX8M errata document [1], there is an I2C spec
> > > violation when the I2C clock frequency is 400 kHz:
> > >
> > > "e7805: I2C: When the I2C clock speed is configured for 400 kHz, the
> > > SCL low period violates the I2C spec of 1.3 uS min"
> > > Avoid this problem by running I2C at 100 kHz instead.
> >
> > Does this fix a real bug? The same issue is present with the i.MX6 I2C
> > controllers, but we are still running a lot of i2c busses on i.MX6
> > based boards at 400kHz, with no issues whatsoever.
> >
>
> We've definitely seen issues running at 400kHz with the librem5 devkit
> and it's using the i.MX8MQ.
I'm not claiming that the erratum will not cause any issues on a random
system, as that's obviously dependent on the board design and connected
i2c slaves. All I'm claiming is that the i.MX6 has the same erratum and
we have no issues with running those busses at 400KHz on the RDU2
board, which is pretty close to the Ultra board that is changed by this
specific patch.
But then IIRC you don't need to reduce the i2c speed all the way to
100KHz to work around the low time violation. You only need to reduce
it slightly to to 375KHz to get in line with the i2c spec.
Most of the i2c issue I've seen in the wild have nothing to do with the
host controller, but are caused by issues in board design, like weak
pull-ups or ground bounces.
Regards,
Lucas
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next prev parent reply other threads:[~2019-05-23 15:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-13 14:02 [PATCH] arm64: dts: imx8mq-zii-ultra: Operate I2C at 100kHz Fabio Estevam
2019-05-13 14:07 ` Lucas Stach
2019-05-14 12:11 ` Fabio Estevam
2019-05-23 13:19 ` Angus Ainslie
2019-05-23 15:01 ` Lucas Stach [this message]
2019-06-27 15:35 ` Chris Healy
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