From mboxrd@z Thu Jan 1 00:00:00 1970 Delivery-date: Mon, 30 Jan 2023 19:36:11 +0100 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by lore.white.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pMZ0m-007tMx-Um for lore@lore.pengutronix.de; Mon, 30 Jan 2023 19:36:11 +0100 Received: from bombadil.infradead.org ([2607:7c80:54:3::133]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1pMZ0j-0003Za-Rt for lore@pengutronix.de; Mon, 30 Jan 2023 19:36:10 +0100 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=FNu1jZuFutD4wSh06+XpTeOOWDbZTsaYjnqXsWcPspM=; b=eYyNY9o0PNhXbA2/47G2a611+5 g3h/RUrP63e/jG2Gb2Kw9jeILTjPhh82+fGoWowwxAshsoviaRBdK+N6hWdwASBKlpwewlchGk05F wdFF3PX0F2SWFynSOl9SC8YiWF9SPTvEK+dxiavTPz+ZGgU37k2F4k7WiwhZ3wjHFPTsR/iMEN4Zk A0zQSpFKMhG/G/kSoyMfj9Px4YAjnFT+vTuFJQwfSGwIQxt4YVm46iF6HAYVF6eMuuhxBjTihDJDG OGsmxwHJdN8jC7Ptrd1oBEBV6R1QLt9tmA31+loqEXnHRGO2Ew78g/7+d7T7DZvlYdmb0VaRNB/r0 tc75fISw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pMYzG-0052jv-Ny; Mon, 30 Jan 2023 18:34:38 +0000 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pMYyh-0052WT-UF for barebox@lists.infradead.org; Mon, 30 Jan 2023 18:34:08 +0000 Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1pMYye-00031f-50 for barebox@lists.infradead.org; Mon, 30 Jan 2023 19:34:00 +0100 Received: from sha by ptx.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1pMT6e-0002J5-Cm; Mon, 30 Jan 2023 13:17:52 +0100 Date: Mon, 30 Jan 2023 13:17:52 +0100 From: Sascha Hauer To: John Watts Cc: barebox@lists.infradead.org Message-ID: <20230130121752.GR13319@pengutronix.de> References: <20230126185643.104049-1-contact@jookia.org> <20230130102727.GQ13319@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-Accept-Language: de,en X-Accept-Content-Type: text/plain User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230130_103404_054146_B32C6B80 X-CRM114-Status: GOOD ( 28.34 ) X-BeenThere: barebox@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "barebox" X-SA-Exim-Connect-IP: 2607:7c80:54:3::133 X-SA-Exim-Mail-From: barebox-bounces+lore=pengutronix.de@lists.infradead.org X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on metis.ext.pengutronix.de X-Spam-Level: X-Spam-Status: No, score=-3.9 required=4.0 tests=AWL,BAYES_00, DATE_IN_PAST_06_12,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Subject: Re: [PATCH] I2C: i.MX: early: Use internal udelay X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on metis.ext.pengutronix.de) On Mon, Jan 30, 2023 at 09:42:53PM +1100, John Watts wrote: > On Mon, Jan 30, 2023 at 11:27:27AM +0100, Sascha Hauer wrote: > > This takes around 5 times too long on a i.MX8MM and around 50 times too > > long on a i.MX6Q. This was measured under a regular barebox on the > > shell. In an early environment with MMU disabled it takes 730 times too > > long. > > Yikes! I'm glad I broke this in to its own patch then. :) > > I did copy this code from these boards: > > arch/arm/boards/cm-fx6/lowlevel.c > arch/arm/boards/skov-imx6/lowlevel.c > arch/arm/boards/technexion-wandboard/lowlevel.c > arch/arm/mach-imx/xload-gpmi-nand.c > arch/arm/mach-imx/imx6-mmdc.c (uses 1000 loops) > > Maybe it's time for an i.MX6-wide early udelay? i.MX6 is not enough, the code could run on other i.MX SoCs as well. > Though this code might break if its timing is already wrong. > > > Maybe we could do this: > > > > static void __udelay(void *base, int us) > > { > > int i; > > > > for (i = 0; i < us * 4; i++) > > readb(base); > > } > > > > The time spent for a register read depends on the bus clock which > > doesn't change that much between the different SoCs. > > This seems like a better solution if you've tested it, I'm not too sure > how to check this. Would I just then specify the controller as the base? Yes, the I2C controller base should be passed here. I tested this with a call to this udelay function with a sufficiently great number of microseconds surrounded by a printf. > > Though the actual goal of the code is to wait for the controller to bestable. > Maybe there's a better way than a delay? I briefly looked into this, but the commit history of both barebox or Linux do not give a real conclusion what we are waiting here for. Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |