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 X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 30B72C07E95 for ; Tue, 20 Jul 2021 14:41:17 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C7A2D6101E for ; Tue, 20 Jul 2021 14:41:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C7A2D6101E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ravnborg.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 360EF6E40A; Tue, 20 Jul 2021 14:41:16 +0000 (UTC) Received: from mx1.smtp.larsendata.com (mx1.smtp.larsendata.com [91.221.196.215]) by gabe.freedesktop.org (Postfix) with ESMTPS id 81AD86E40A for ; Tue, 20 Jul 2021 14:41:14 +0000 (UTC) Received: from mail01.mxhotel.dk (mail01.mxhotel.dk [91.221.196.236]) by mx1.smtp.larsendata.com (Halon) with ESMTPS id 88b76b19-e968-11eb-9082-0050568c148b; Tue, 20 Jul 2021 14:41:14 +0000 (UTC) Received: from ravnborg.org (80-162-45-141-cable.dk.customer.tdc.net [80.162.45.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: sam@ravnborg.org) by mail01.mxhotel.dk (Postfix) with ESMTPSA id B9164194B81; Tue, 20 Jul 2021 16:41:27 +0200 (CEST) Date: Tue, 20 Jul 2021 16:41:10 +0200 X-Report-Abuse-To: abuse@mxhotel.dk From: Sam Ravnborg To: Geert Uytterhoeven Subject: Re: [PATCH resend 2/5] video: fbdev: ssd1307fb: Simplify ssd1307fb_update_display() Message-ID: References: <20210714145804.2530727-1-geert@linux-m68k.org> <20210714145804.2530727-3-geert@linux-m68k.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux Fbdev development list , David Airlie , Linux Kernel Mailing List , DRI Development Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Geert, On Tue, Jul 20, 2021 at 09:43:22AM +0200, Geert Uytterhoeven wrote: > Hi Sam, > > On Mon, Jul 19, 2021 at 9:05 PM Sam Ravnborg wrote: > > On Wed, Jul 14, 2021 at 04:58:01PM +0200, Geert Uytterhoeven wrote: > > > Simplify the nested loops to handle conversion from linear frame buffer > > > to ssd1307 page layout: > > > 1. Move last page handling one level up, as the value of "m" is the > > > same inside a page, > > > 2. array->data[] is filled linearly, so there is no need to > > > recalculate array_idx over and over again; a simple increment is > > > sufficient. > > > > > > Signed-off-by: Geert Uytterhoeven > > > --- > > > drivers/video/fbdev/ssd1307fb.c | 17 ++++++++++------- > > > 1 file changed, 10 insertions(+), 7 deletions(-) > > > > > > diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c > > > index e6b6263e3bef847f..6d7bd025bca1a175 100644 > > > --- a/drivers/video/fbdev/ssd1307fb.c > > > +++ b/drivers/video/fbdev/ssd1307fb.c > > > @@ -158,6 +158,7 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par) > > > u8 *vmem = par->info->screen_buffer; > > > unsigned int line_length = par->info->fix.line_length; > > > unsigned int pages = DIV_ROUND_UP(par->height, 8); > > > + u32 array_idx = 0; > > > int ret, i, j, k; > > > > > > array = ssd1307fb_alloc_array(par->width * pages, SSD1307FB_DATA); > > > @@ -194,19 +195,21 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par) > > > */ > > > > > > for (i = 0; i < pages; i++) { > > > + int m = 8; > > > + > > > + /* Last page may be partial */ > > > + if (i + 1 == pages && par->height % 8) > > > + m = par->height % 8; > > > for (j = 0; j < par->width; j++) { > > > - int m = 8; > > > - u32 array_idx = i * par->width + j; > > > - array->data[array_idx] = 0; > > > - /* Last page may be partial */ > > > - if (i + 1 == pages && par->height % 8) > > > - m = par->height % 8; > > > + u8 data = 0; > > > + > > > for (k = 0; k < m; k++) { > > If the last page is partial then m will be less than 8 for all bytes in > > j = 0..par-width - but m should only be less than 8 for the last > > iteration of the loop. > > > > Do I miss something or is the code buggy? > > "the loop" is the j-loop? > If m is less than 8 for the last page, it should be less than 8 for > all iterations of j, as all last bytes in each "line" (visible > row) are partial, cfr. the comments above the code, explaining the > representation of the screen. OK, then the code works as intended. I had not read the comments and just assume it was only the last byte that was in need of a special treatment. So code is fine: Acked-by: Sam Ravnborg > > > > u8 byte = vmem[(8 * i + k) * line_length + > > > j / 8]; > > > u8 bit = (byte >> (j % 8)) & 1; > > > - array->data[array_idx] |= bit << k; > > > + data |= bit << k; > > > } > > > + array->data[array_idx++] = data; > > > } > > > } > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds