From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261941AbVDVEJn (ORCPT ); Fri, 22 Apr 2005 00:09:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261943AbVDVEJm (ORCPT ); Fri, 22 Apr 2005 00:09:42 -0400 Received: from mail03.powweb.com ([66.152.97.36]:25099 "EHLO mail03.powweb.com") by vger.kernel.org with ESMTP id S261941AbVDVEJi (ORCPT ); Fri, 22 Apr 2005 00:09:38 -0400 From: Richard Drummond Organization: Private To: linux-fbdev-devel@lists.sourceforge.net Subject: [PATCH] Better PLL frequency matching for tdfxfb driver Date: Thu, 21 Apr 2005 22:58:00 -0500 User-Agent: KMail/1.7.2 Cc: linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-Id: <200504212258.00570.evilrich@rcdrummond.net> Content-Type: Multipart/Mixed; boundary="Boundary-00=_IZHaCqkOpSzY1nK" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --Boundary-00=_IZHaCqkOpSzY1nK Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Disposition: inline Attached is a patch against 2.6.11.7 which improves the PLL frequency matching in the tdfxfb driver. Instead of requiring 64260 iterations to obtain the closest supported PLL frequency, this code does it with the same degree of accuracy in at most 768 iterations. Signed-off-by: Richard Drummond --Boundary-00=_IZHaCqkOpSzY1nK Content-Type: text/x-diff; charset="us-ascii"; name="tdfxfb_pll_fix.diff" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="tdfxfb_pll_fix.diff" --- drivers/video/tdfxfb.c_orig 2005-04-20 15:04:23.000000000 -0500 +++ drivers/video/tdfxfb.c 2005-04-21 09:26:18.000000000 -0500 @@ -320,30 +320,40 @@ static u32 do_calc_pll(int freq, int* freq_out) { - int m, n, k, best_m, best_n, best_k, f_cur, best_error; + int m, n, k, best_m, best_n, best_k, best_error; int fref = 14318; - /* this really could be done with more intelligence -- - 255*63*4 = 64260 iterations is silly */ best_error = freq; best_n = best_m = best_k = 0; - for (n = 1; n < 256; n++) { - for (m = 1; m < 64; m++) { - for (k = 0; k < 4; k++) { - f_cur = fref*(n + 2)/(m + 2)/(1 << k); - if (abs(f_cur - freq) < best_error) { - best_error = abs(f_cur-freq); - best_n = n; - best_m = m; - best_k = k; - } + + for (k = 3; k >= 0; k--) { + for (m = 63; m >= 0; m--) { + /* Estimate value of n that produces target frequency with current m and k */ + int n_estimated = (freq * (m + 2) * (1 << k) / fref) - 2; + + /* Search neighborhood of estimated n */ + for (n = max(0, n_estimated - 1); n <= min(255, n_estimated + 1); n++) { + /* Calculate PLL freqency with current m, k and estimated n */ + int f = fref * (n + 2) / (m + 2) / (1 << k); + int error = abs (f - freq); + + /* If this is the closest we've come to the target frequency + * then remember n, m and k */ + if (error < best_error) { + best_error = error; + best_n = n; + best_m = m; + best_k = k; + } } } } + n = best_n; m = best_m; k = best_k; *freq_out = fref*(n + 2)/(m + 2)/(1 << k); + return (n << 8) | (m << 2) | k; } --Boundary-00=_IZHaCqkOpSzY1nK--