From: Wolfram Sang <wsa@the-dreams.de>
To: Chris Brandt <Chris.Brandt@renesas.com>
Cc: "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>,
Simon Horman <horms+renesas@verge.net.au>,
Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH v2] i2c: riic: remove fixed clock restriction
Date: Fri, 13 Oct 2017 23:51:09 +0200 [thread overview]
Message-ID: <20171013215109.l35j652amscnrsfe@ninjato> (raw)
In-Reply-To: <SG2PR06MB11658FE2DCDC2A50FA5ED7258A480@SG2PR06MB1165.apcprd06.prod.outlook.com>
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Hi Chris,
> How about a range of -4% to +2% ?
I am fine with a range in general, but I don't like +x% because we should never
be faster than requested. Clients may have problems with that.
> Technically, to do it right, to calculate the ACTUAL I2C baud rate, you
> have to take into effect the load resistance and capacitance of the
> lines in order to factor in the rise and fall times correctly. Of course
We have those generic bindings upstream:
- i2c-scl-falling-time-ns
Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
specification.
- i2c-scl-internal-delay-ns
Number of nanoseconds the IP core additionally needs to setup SCL.
- i2c-scl-rising-time-ns
Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C
specification.
- i2c-sda-falling-time-ns
Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
specification.
So far, that was all that is needed, however...
> Just live with the fact that the speed might be off by 4%.
... as I said before, I won't force it on you for the frequencies you want to
support.
Regards,
Wolfram
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next prev parent reply other threads:[~2017-10-13 21:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-29 17:16 [PATCH v2] i2c: riic: remove fixed clock restriction Chris Brandt
2017-10-11 15:20 ` Chris Brandt
2017-10-13 18:56 ` Wolfram Sang
2017-10-13 19:37 ` Chris Brandt
2017-10-13 21:51 ` Wolfram Sang [this message]
2017-10-16 17:21 ` Chris Brandt
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