Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966025Ab3FTULT (ORCPT ); Thu, 20 Jun 2013 16:11:19 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:43783 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965998Ab3FTULR (ORCPT ); Thu, 20 Jun 2013 16:11:17 -0400 Date: Thu, 20 Jun 2013 21:06:24 +0100 From: Russell King - ARM Linux To: Sebastian Hesselbarth Cc: David Airlie , Darren Etheridge , linux-arm-kernel@lists.infradead.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] drm/i2c: tda998x: fix sync generation and calculation Message-ID: <20130620200624.GQ2718@n2100.arm.linux.org.uk> References: <1371757563-27862-1-git-send-email-sebastian.hesselbarth@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1371757563-27862-1-git-send-email-sebastian.hesselbarth@gmail.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2414 Lines: 75 On Thu, Jun 20, 2013 at 09:46:03PM +0200, Sebastian Hesselbarth wrote: > + ref_pix = 3 + mode->hsync_start - mode->hdisplay; > + de_pix_s = mode->htotal - mode->hdisplay; > + de_pix_e = de_pix_s + mode->hdisplay; > + hs_pix_s = mode->hsync_start - mode->hdisplay; > + hs_pix_e = hs_pix_s + mode->hsync_end - mode->hsync_start; Correct, however, these can be simplified. For de_pix_e: de_pix_e = de_pix_s + mode->hdisplay; de_pix_s = mode->htotal - mode->hdisplay; Putting de_pix_s into de_pix_e's equation, you get: de_pix_e = mode->htotal - mode->hdisplay + mode->hdisplay; which ends up simply as: de_pix_e = mode->htotal; Now, doing the same for hs_pix_e: hs_pix_e = mode->hsync_start - mode->hdisplay + mode->hsync_end - mode->hsync_start; which ends up as: hs_pix_e = mode->hsync_end - mode->hdisplay; So overall these come out as: de_pix_e = mode->htotal; de_pix_s = mode->htotal - mode->hdisplay; hs_pix_e = mode->hsync_end - mode->hdisplay; hs_pix_s = mode->hsync_start - mode->hdisplay; I've listed them in reverse order because it makes more sense to me when thinking about it. What we're basically doing is rotating this by hdisplay pixel clocks to the left, so using abbreviations: ht=htotal hds=hdisplay start hde=hdisplay end hss=hsync_start hse=hsync_end 0 ht hds hde hss hse | |-----------------------------------|----|---|----| becomes: 0 ht 0 hss hse hds hde |----|---|----|-----------------------------------| and from that you can visualize taking hdisplay (being hde-hds) off each timing parameter modulo htotal gives you the above equations. These calculations are the same as what was originally in the driver: + de_start = mode->htotal - mode->hdisplay; + de_end = mode->htotal; + hs_start = mode->hsync_start - mode->hdisplay; + hs_end = mode->hsync_end - mode->hdisplay; when it was first committed. This is otherwise exactly what I came up with which gets my TV working again in HDMI mode. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/