From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C81DC433F5 for ; Thu, 3 Mar 2022 21:33:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233250AbiCCVeB (ORCPT ); Thu, 3 Mar 2022 16:34:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231389AbiCCVeB (ORCPT ); Thu, 3 Mar 2022 16:34:01 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2198F48300 for ; Thu, 3 Mar 2022 13:33:14 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8292061D48 for ; Thu, 3 Mar 2022 21:33:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 51068C004E1; Thu, 3 Mar 2022 21:33:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646343193; bh=AsnyLkVWz/WbkX9L7YpIhoPjjwoxwkgl406FsGxHgn8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UhSfv8373qAHE+Y+ynglO2DPDlVf0Vt4Id04it2nbiTWthm68Xn/fMH7urNmTC2Z8 LU3Zl2VVwJ+Do0Rq9S6dWqcnPn7m7Pg0lt9XCfdD7FM1PucuxnwWz5e427dN19mKNn 18BdVDesz7pZdG1vsDrPXYN7IBIxtcaj6LNQ0MAQqbeBeJ2kkvxX6kvDd+HdoENSgA QXqI0EHPk1lvn8/xL4hm9PnDc8Wc5VKPqbBr7evUMr8lX6ixdAmgN6O5ULW8Dqd5g9 n2z73oEc3UA5DF69qWSFzhva9xTUnpum5GVGRQC1HbqK/HlCJpaYI3E+fwpBavMKRR c1uAd3tDHGc6g== Date: Thu, 3 Mar 2022 22:33:10 +0100 From: Wolfram Sang To: Ian Dannapel , Oleksij Rempel Cc: "linux-i2c@vger.kernel.org" Subject: Re: i2c-imx.c: Unnecessary delay slowing down i2c communication Message-ID: Mail-Followup-To: Wolfram Sang , Ian Dannapel , Oleksij Rempel , "linux-i2c@vger.kernel.org" References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="QCxX4FJK+pK3xDd+" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org --QCxX4FJK+pK3xDd+ Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Mar 03, 2022 at 03:19:00PM +0000, Ian Dannapel wrote: > Hello I=C2=B2C Driver Maintainers, Adding the i2c-imx maintainer to CC. >=20 > please excuse me if I am not following the right steps to report a questi= on. I did not find consensus between all instructions that I read. >=20 > We noted that on the IMX i2c driver, at the i2c_imx_start funtion, some s= leep/delay was introduced without any apparent reason: > Line 448 at: https://github.com/Freescale/linux-fslc/commit/3a5ee18d2a32= bda6b9a1260136f6805848e3839d=20 > Line 528 at: https://github.com/Freescale/linux-fslc/commit/2b899f34e1db= 9adef8716d07e872a800dfa60790 > Line 200 at: https://github.com/Freescale/linux-fslc/commit/43309f3b5213= 02bb66c4c9e66704dd3675e4d725 >=20 > This sleep causes a pretty big latency overhead on I=C2=B2C writes and no= IMX8MP document states the need of this delay on the controller. NXP Suppo= rt also informed that this delay might not be needed. > Some early tests with removing this delay completely showed a great reduc= tion on the write latency and no problems with the communication. >=20 > But since we want a stable and fast communication, I ask here again if so= meone knows the reason or the need for this delay when starting to communic= ate on the I2C bus. >=20 > I appreciate any response and if further information is needed, I can gla= dly report it. >=20 >=20 > Best regards, > Ian Dannapel > ian.dannapel@iris-sensing.com > =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2= =80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80= =A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 = =E2=80=A2 =E2=80=A2 =E2=80=A2 =E2=80=A2 > iris-GmbH > infrared & intelligent sensors > Schnellerstra=C3=9Fe 1-5 | 12439 Berlin > www.iris-sensing.com >=20 >=20 >=20 >=20 >=20 --QCxX4FJK+pK3xDd+ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEOZGx6rniZ1Gk92RdFA3kzBSgKbYFAmIhNBIACgkQFA3kzBSg KbbW4g/+LuNhbh8LK/ZDEbQA1DAoPdNH126YhFvvfjknVojwUb3pU2f05A+2I5JY l+yBNTDrheziLr2EyLF2aTbBn7rsgEtj8J4e+mo7d905JFPwJQcWV0uHM/Da+/ry h8uWbhvgDl+TBbPr5fUYsqHx2x6Ka2n+e8hFjp6B09KGhqaiWrsLFBxp+f/wakN4 fDJqHrkkUsm6sWH9oRPXL79Gy8DG5HCL0rpVpCI9yNLFsFYZKKljglrho71fpaNz UomjAv0nfsE0+Tr/m4ozsNTwH0gqG+Y3bDpLUtP6ne93o/qivzSGG7Pciqno/Q32 +W3w+64gkwyWdRqob1ANgRecZlDii/g/Gjx+bIjZvvcUs3MFDDkiv1wj7kuHEr1O DS865aT9HNhF9q4AL2lufT6uv0OA6zrgTMJRn+FWFrYWI4+qEsYaQbm5/RY4QyNm 0T6hAfnabPIgyr8vVvoMkWIrVHW0Gz+kMfQ8NxPZ6iulKbiLJNdjeGGg8bDIU5dP iHymylyu1cImDmSyZOdRfgPEM9VwHrpFgzFxEviZAv4ewa/SQueT7LANQZmhgvcF iS1T+acdEGtHctZ+ow7Mdd2xfM5MHc2HQZqqzHpSWgfEHN13Q/jCAmvrRvHG6sZY VP91IHgDlsrjCITWCrtwD8YToyzItZs78EDUt2FSfC0INPyBwqQ= =/wnE -----END PGP SIGNATURE----- --QCxX4FJK+pK3xDd+--