From: balbi@ti.com (Felipe Balbi)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3] i2c: omap: improve duty cycle on SCL
Date: Thu, 18 Jun 2015 12:25:58 -0500 [thread overview]
Message-ID: <20150618172558.GC27790@saruman.tx.rr.com> (raw)
In-Reply-To: <55827CD7.7030207@nokia.com>
On Thu, Jun 18, 2015 at 10:09:59AM +0200, Alexander Sverdlin wrote:
> Hello Felipe,
>
> On 17/06/15 21:31, ext Felipe Balbi wrote:
> > With this patch we try to be as close to 50%
> > duty cycle as possible. The reason for this
> > is that some devices present an erratic behavior
> > with certain duty cycles.
> >
> > One such example is TPS65218 PMIC which fails
> > to change voltages when running @ 400kHz and
> > duty cycle is lower than 34%.
> >
> > The idea of the patch is simple:
> >
> > calculate desired scl_period from requested scl
> > and use 50% for tLow and 50% for tHigh.
> >
> > tLow is calculated with a DIV_ROUND_UP() to make
> > sure it's slightly higher than tHigh and to make
> > sure that we end up within I2C specifications.
>
> if you refuse to change the calculations to achieve maximum possible
> bus rate (as I've shown you with SCLL=9 and SCLH=9), maybe you want to
> change the description? Because you are doing something else than is
> written here. You are only in spec because you are not doing 50% duty
> cycle. And you didn't mention here that you lower the bus speed below
> 400kHz to achieve this.
and there's a comment where the calculation goes which states "as close
to 50% as possible but we make sure tLow is higher than tHigh so we're
still within spec".
--
balbi
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From: Felipe Balbi <balbi@ti.com>
To: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Cc: ext Felipe Balbi <balbi@ti.com>,
wsa@the-dreams.de, Tony Lindgren <tony@atomide.com>,
Dave Gerlach <d-gerlach@ti.com>, Nishanth Menon <nm@ti.com>,
linux-i2c@vger.kernel.org,
Linux OMAP Mailing List <linux-omap@vger.kernel.org>,
Linux ARM Kernel Mailing List
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3] i2c: omap: improve duty cycle on SCL
Date: Thu, 18 Jun 2015 12:25:58 -0500 [thread overview]
Message-ID: <20150618172558.GC27790@saruman.tx.rr.com> (raw)
In-Reply-To: <55827CD7.7030207@nokia.com>
[-- Attachment #1: Type: text/plain, Size: 1353 bytes --]
On Thu, Jun 18, 2015 at 10:09:59AM +0200, Alexander Sverdlin wrote:
> Hello Felipe,
>
> On 17/06/15 21:31, ext Felipe Balbi wrote:
> > With this patch we try to be as close to 50%
> > duty cycle as possible. The reason for this
> > is that some devices present an erratic behavior
> > with certain duty cycles.
> >
> > One such example is TPS65218 PMIC which fails
> > to change voltages when running @ 400kHz and
> > duty cycle is lower than 34%.
> >
> > The idea of the patch is simple:
> >
> > calculate desired scl_period from requested scl
> > and use 50% for tLow and 50% for tHigh.
> >
> > tLow is calculated with a DIV_ROUND_UP() to make
> > sure it's slightly higher than tHigh and to make
> > sure that we end up within I2C specifications.
>
> if you refuse to change the calculations to achieve maximum possible
> bus rate (as I've shown you with SCLL=9 and SCLH=9), maybe you want to
> change the description? Because you are doing something else than is
> written here. You are only in spec because you are not doing 50% duty
> cycle. And you didn't mention here that you lower the bus speed below
> 400kHz to achieve this.
and there's a comment where the calculation goes which states "as close
to 50% as possible but we make sure tLow is higher than tHigh so we're
still within spec".
--
balbi
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next prev parent reply other threads:[~2015-06-18 17:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-17 19:31 [PATCH v3] i2c: omap: improve duty cycle on SCL Felipe Balbi
2015-06-17 19:31 ` Felipe Balbi
2015-06-18 8:09 ` Alexander Sverdlin
2015-06-18 8:09 ` Alexander Sverdlin
2015-06-18 17:25 ` Felipe Balbi [this message]
2015-06-18 17:25 ` Felipe Balbi
2015-07-09 19:42 ` Wolfram Sang
2015-07-09 19:42 ` Wolfram Sang
2015-07-10 17:27 ` Felipe Balbi
2015-07-10 17:27 ` Felipe Balbi
2015-08-13 14:36 ` Felipe Balbi
2015-08-13 14:36 ` Felipe Balbi
[not found] ` <CAFqkuUbO1CZ8bu8g8O7SsLF-0nUV274GZ08=6J1sVS4Foy+_EA@mail.gmail.com>
2015-08-18 14:43 ` Felipe Balbi
2015-08-18 14:43 ` Felipe Balbi
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