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=-8.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 60E32C2D0A3 for ; Mon, 9 Nov 2020 14:25:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F28DB206ED for ; Mon, 9 Nov 2020 14:25:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ti.com header.i=@ti.com header.b="sKPECRxH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730084AbgKIOZa (ORCPT ); Mon, 9 Nov 2020 09:25:30 -0500 Received: from fllv0015.ext.ti.com ([198.47.19.141]:36100 "EHLO fllv0015.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730035AbgKIOZa (ORCPT ); Mon, 9 Nov 2020 09:25:30 -0500 Received: from lelv0266.itg.ti.com ([10.180.67.225]) by fllv0015.ext.ti.com (8.15.2/8.15.2) with ESMTP id 0A9EPIQc067321; Mon, 9 Nov 2020 08:25:18 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1604931918; bh=DQS1axFy+zJL+GmIcwNyhOuwva/Tl/Qsxgv0mCkWaLg=; h=Subject:To:CC:References:From:Date:In-Reply-To; b=sKPECRxH6urdAytIe8v6N2rrDUfldhU7Kn8N+3RnmS2QOTZS7SrbIUGX4hcTckEsh x1wVer5MS9HGoSQwjV/2gd23IuqznpnreTcWunVXwMIB3wHJntP3/uGZ9ZgWvxcdgn nG0WDQIkZ2qyB5cZxOxoBbmPPLU9STAtENVac9Og= Received: from DFLE109.ent.ti.com (dfle109.ent.ti.com [10.64.6.30]) by lelv0266.itg.ti.com (8.15.2/8.15.2) with ESMTPS id 0A9EPItV106032 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 9 Nov 2020 08:25:18 -0600 Received: from DFLE113.ent.ti.com (10.64.6.34) by DFLE109.ent.ti.com (10.64.6.30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1979.3; Mon, 9 Nov 2020 08:25:18 -0600 Received: from fllv0039.itg.ti.com (10.64.41.19) by DFLE113.ent.ti.com (10.64.6.34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1979.3 via Frontend Transport; Mon, 9 Nov 2020 08:25:18 -0600 Received: from [192.168.2.6] (ileax41-snat.itg.ti.com [10.172.224.153]) by fllv0039.itg.ti.com (8.15.2/8.15.2) with ESMTP id 0A9EPGwY011676; Mon, 9 Nov 2020 08:25:16 -0600 Subject: Re: [PATCH v3 27/56] drm/omap: dsi: do bus locking in host driver To: Sebastian Reichel CC: Laurent Pinchart , Nikhil Devshatwar , , , Sekhar Nori , Tony Lindgren , "H . Nikolaus Schaller" References: <20201105120333.947408-1-tomi.valkeinen@ti.com> <20201105120333.947408-28-tomi.valkeinen@ti.com> <20201109095255.GX6029@pendragon.ideasonboard.com> <3c9eefd3-99bb-edce-f6ac-2fec3678743b@ti.com> <20201109132705.6n7h3ogsrlciw5nf@earth.universe> From: Tomi Valkeinen Message-ID: Date: Mon, 9 Nov 2020 16:25:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201109132705.6n7h3ogsrlciw5nf@earth.universe> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Precedence: bulk List-ID: X-Mailing-List: linux-omap@vger.kernel.org On 09/11/2020 15:27, Sebastian Reichel wrote: > Hi, > > On Mon, Nov 09, 2020 at 12:08:33PM +0200, Tomi Valkeinen wrote: >> On 09/11/2020 11:52, Laurent Pinchart wrote: >>> Hi Tomi, >>> >>> Thank you for the patch. >>> >>> On Thu, Nov 05, 2020 at 02:03:04PM +0200, Tomi Valkeinen wrote: >>>> From: Sebastian Reichel >>>> >>>> This moves the bus locking into the host driver and unexports >>>> the custom API in preparation for drm_panel support. >>>> >>>> Signed-off-by: Sebastian Reichel >>>> Signed-off-by: Tomi Valkeinen >> >> >> >>>> static int dsicm_update(struct omap_dss_device *dssdev, >>>> @@ -739,7 +704,6 @@ static int dsicm_update(struct omap_dss_device *dssdev, >>>> dev_dbg(&ddata->dsi->dev, "update %d, %d, %d x %d\n", x, y, w, h); >>>> >>>> mutex_lock(&ddata->lock); >>>> - src->ops->dsi.bus_lock(src); >>>> >>>> r = dsicm_wake_up(ddata); >>>> if (r) >>>> @@ -761,11 +725,9 @@ static int dsicm_update(struct omap_dss_device *dssdev, >>>> if (r) >>>> goto err; >>>> >>>> - /* note: no bus_unlock here. unlock is src framedone_cb */ >>>> - mutex_unlock(&ddata->lock); >>>> + /* note: no unlock here. unlock is src framedone_cb */ >>> >>> This change isn't described in the commit message. Could you explain why >>> it's needed ? Locking a mutex in a function and unlocking it elsewhere >>> always scares me. >> >> Good catch. I don't know why it is needed. I don't think it is, as >> the dsi driver handles the bus lock. >> >> Sebastian, what was the reason for this lock? >> >> Note that this goes away in the series, and there's no such lock >> in the end. > > It's not really a change. What this patch basically does is to fold > src->ops->dsi.bus_lock(src) into mutex_lock(&ddata->lock), so that > there is only a single locking mechanism. This function previously > had a matching pair of mutex_lock/unlock for ddata->lock, but the > bus was not locked paired. So after conversion the lock must not be > free'd here. Hmm, but taking the bus_lock is moved into dsi.c (dsi_bus_lock/unlock). Previously the panel called that directly via the dsi_ops->bus_lock(), but afaics bus_lock is now taken in dsi_update(), which is called from the panel. But in addition to that, this patch makes the panel driver keep the ddata->lock during the update, which is meant to only protect the ddata. > My understanding is, that this is because the bus must not be used > until the update has been done. Yes, and not only about the update, but e.g. prevent sending backlight commands while reading the framebuffer memory. Tomi -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki