From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH] i2c: designware: use {readl|writel}_relaxed instead of readl/writel Date: Tue, 13 Jan 2015 15:36:54 +0100 Message-ID: <20150113143654.GG7660@katana> References: <1418279201-3886-1-git-send-email-jszhang@marvell.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="MiFvc8Vo6wRSORdP" Return-path: Content-Disposition: inline In-Reply-To: <1418279201-3886-1-git-send-email-jszhang-eYqpPyKDWXRBDgjK7y7TUQ@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jisheng Zhang Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-i2c@vger.kernel.org --MiFvc8Vo6wRSORdP Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Dec 11, 2014 at 02:26:41PM +0800, Jisheng Zhang wrote: > readl/writel is too expensive especially on Cortex A9 w/ outer L2 cache. > This introduces i2c read/write errors on Marvell BG2/BG2Q SoCs when there > are heavy L2 cache maintenance operations at the same time. Reading this again, I got a question: Really read/write errors? I would think that there is a performance penalty because of the memory barriers. But errors? > The driver does not perform DMA, so it's safe to use the relaxed version. > From another side, the relaxed io accessor macros are available on all > architectures now, so we can use the relaxed versions instead. Can the designware core make use of DMA in theory? --MiFvc8Vo6wRSORdP Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUtS2GAAoJEBQN5MwUoCm2svAQAIpRt3q0aHH0xGwK8rt2P91x ZJVUcF2YrP1KPo14LaP6N0lPAjzathtXBHOPr5udB7+zoMJBPGdHXrPRP9x7WmAY 89avemgEFOdrhuDcBkr2BXhn6hsRs5HJlu9x0/z/HfLK4Cwmoh9BhB4CTOYT4VnL PlH60kJBSfAxh2llM/k024o70p8uNnN0ODe4kIDiBcbqnWTOBjTT4ecjT0qehrl/ T7ghYQOFzl4vwzgvMNFrxMNb4n1eksktxn5qua/HGrloU8l1iJ1rRBSBkw1xfHJp /2DZv+inHvuyLPvyNLEld8i/4Q0QgA/D8zL7lNhLuA7pmwUmv496NJpkX++xD+da SJOZuzKGT30lUUQLMLUEkeG89kLqMkqbbsdrC4RDw6LP077h/p53rmFuVGr9Yc3B 3Nk5TfeOK34mq4eTLvNerAwg+y6e6T7GekVGvRjR6gGcSQPsD8SD3sEpVSgbFzhY 8xM3yDBROS6/kepaHGAXSF3nyxYg2ask8Cdrirg9pRwHm6OHCTBl8S5q6hYAzINu ysJTSor0O64aiwxhH/dVzEEqHbf8X/0/rHLrxomoVPS0l4lmgqH538to59vYQ1+C HR80GYPgkBL8EnwNo06VuYvoEpOO8c1/IDlSFpbkaWO0RV9Wid16ImvI59EkR28s bxtE2Bu78n1pC4fbYQzG =lfnX -----END PGP SIGNATURE----- --MiFvc8Vo6wRSORdP--