From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keith Packard Subject: Re: [PATCH 1/2] drm/kms: Make i2c buses faster Date: Sat, 28 Jan 2012 17:26:25 -0800 Message-ID: <86sjizqoxq.fsf@sumi.keithp.com> References: <201201281107.09266.jdelvare@suse.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0618534597==" Return-path: Received: from keithp.com (home.keithp.com [63.227.221.253]) by gabe.freedesktop.org (Postfix) with ESMTP id 98A7E9E878 for ; Sat, 28 Jan 2012 17:26:30 -0800 (PST) In-Reply-To: <201201281107.09266.jdelvare@suse.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: Jean Delvare , dri-devel@lists.freedesktop.org Cc: Eugeni Dodonov List-Id: dri-devel@lists.freedesktop.org --===============0618534597== Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" --=-=-= Content-Transfer-Encoding: quoted-printable On Sat, 28 Jan 2012 11:07:09 +0100, Jean Delvare wrote: > A udelay value of 20 leads to an I2C bus running at only 25 kbps. I2C > devices can typically operate faster than this, 50 kbps should be fine > for all devices (and compliant devices can always stretch the clock if > needed.) >=20 > FWIW, the vast majority of framebuffer drivers set udelay to 10 > already. So set it to 10 in DRM drivers too, this will make EDID block > reads faster. We might even lower the udelay value later if no problem > is reported. That runs the DDC at a whopping 50kbps, which is half of the maximum rate specified in the DDC/CI standard. I don't know if we can count on clock stretching (http://www.i2c-bus.org/clock-stretching/), but if so, I don't know why we wouldn't just go to the standard 100kbps data rate and be done with it. Might be nice to see what frequency Windows uses for i2c; anyone want to pull a vga cable apart and hook up a logic analyser? =2D-=20 keith.packard@intel.com --=-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIVAwUBTySgQTYtFsjWk68qAQgJ4g/9FvsCAZ1305LPyOlFN8oY2k2o5lpiKzd7 tz9WwsMJscL0x2Qs4axs8Ci7c/6221tv2lhbCLxUVJUdfpmWuf9v21rSXM7c61CN fbRQNrePLntO5UIk9a/gz1LhO1YwKo98S9YD/Hj/cGxsH0Tb49y098MxR5KKZN+3 36cQ7k+/CzMz4IErJ4zuh60RCTuK3bEI1XTFNbaIIULnOWw42rQiwf0uTaeXCTVZ AgSFEQzR+071T+sXUJumbgYB4sLZcEj076ksx9pd17Wgt+rply5D0kMCL7v3sKUp 7kDu9p5bBGhR3xJDLY/Ke+jWctrHMwLV6NVk/ulZjteHwT9PgF8Zpvej4cTJf2Mu nWJC/GIeAY6isH2tDW6OO6ih2t6BP2iB1kawfjz1AfD8oLXKjRH39xTYCOi+g8hX iLh+9ONoWyUwxqY+6ASbsDWYWwYFJYHSNwc8g6oEGvH7V6SnoHE99Hex4x/vxFbS dYxwiYON26uD+5fDjWRUc//6xrxs67xsyBisMT5MLpdmQbreJPoysVdQjC8N7wKy cUnr4s3tmo6jKLmz07B1R7acgVbl10CBhrDC1aMV0WhzoiawKkYfId2TFC9LU1q0 jtmCCbkceyT+6ZA8eR1Tztz0jME2x1BDxvucXWJMIrv6RYskh6WNCL2MqC39bPCf JN+pBRPB7c0= =KtPn -----END PGP SIGNATURE----- --=-=-=-- --===============0618534597== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel --===============0618534597==--