From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH v2] i2c: riic: remove fixed clock restriction Date: Fri, 13 Oct 2017 23:51:09 +0200 Message-ID: <20171013215109.l35j652amscnrsfe@ninjato> References: <20170929171637.121262-1-chris.brandt@renesas.com> <20171013185633.lakiw4cu5o22cwjf@ninjato> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="76dla3w63pp2a7qz" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-renesas-soc-owner@vger.kernel.org To: Chris Brandt Cc: "linux-i2c@vger.kernel.org" , "linux-renesas-soc@vger.kernel.org" , Simon Horman , Geert Uytterhoeven List-Id: linux-i2c@vger.kernel.org --76dla3w63pp2a7qz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 n= ever be faster than requested. Clients may have problems with that. > Technically, to do it right, to calculate the ACTUAL I2C baud rate, you= =20 > have to take into effect the load resistance and capacitance of the=20 > lines in order to factor in the rise and fall times correctly. Of course= =20 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%. =2E.. as I said before, I won't force it on you for the frequencies you wan= t to support. Regards, Wolfram --76dla3w63pp2a7qz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEOZGx6rniZ1Gk92RdFA3kzBSgKbYFAlnhNU0ACgkQFA3kzBSg KbYlDQ//ZCXJ/eak9SC3zPg4tPBDatqoZtSmalFz8LqPHZPMUd+KpEsdtSkUnDO7 WsTIor51WWeOJJaBMdlbTqp+g0kwlmA67X9By54VuVJ7xiCTGh4/fI+2sHBSQEv4 c3Re2cmrc8ZFErOuZyPZzrk8unkc/y7L0WL1cXHFfQrmRcSvFimXPu/ImleKMKKz NKTn7IqgV71qvR5cTxaI50UmfbW1dkF2GM6sT1CAjoRf1xBcDmaffg3dTrnsj4is RWYO1dq0uAJKGFz62FNlGo7ulafkLHGcIhFHdAJ0gMMkqBjCIN2/1w/9jxaTjnD/ AOAjlTjXKwZhdZB/E+Z4AXvR4KstpoI5H6IoR8nN9dfISBpNAYn9a2+Kes2lG6ED KM+NZFC9xovBQJOW4/GKXM2uB8Eadu2RGCoP/mpRD2ufzIpIHSqcxt6WaYipj3mI IIEjM6/DZsflBswQz5TkvGWtDNnT7H9t0dAALfnMzxmvnpKl+w1MSbTLVlmnKC5i tfftPFlh7sXrOOewbBK7BLszGkP92LO6HQA5Rehu99dTI1QgXA1p8zGB1PXaEGCR Qp6vOPs2N0NhIRG3MkSRhMzK8EFihnNcdJwDK1w8RR1YGm59LKiW68FcWEFKwvfj mRvTfRay7kIBZ0M7zoHlhjMnQ44bhEXfGvd0FzvOOmkPe/JNbpY= =QmTK -----END PGP SIGNATURE----- --76dla3w63pp2a7qz--