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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 E72E1C433C1 for ; Tue, 23 Mar 2021 19:53:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB69A619C9 for ; Tue, 23 Mar 2021 19:53:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231588AbhCWTx3 (ORCPT ); Tue, 23 Mar 2021 15:53:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231573AbhCWTxM (ORCPT ); Tue, 23 Mar 2021 15:53:12 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41787C061574 for ; Tue, 23 Mar 2021 12:53:12 -0700 (PDT) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 95AE0B1D; Tue, 23 Mar 2021 20:53:08 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1616529188; bh=YwlqFRn0M9BFPQVdD6FUntyPjZt77vZr8VZHyyOCrsg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=F8BEzzazZmkIYLZPdUQuuBsmom2pF1ocb+rZbxV6fjucBH78VhbZCMrAKhvwr64Dp aD9JWfQ1AznsC2BpTV6k8e0WARjOD8qf2BGqoqnOHjOGLtQ7K8B1rTuCGK190nlwyy CgSNrLJSa0vzzkV25c/eJakIocK8GOoHRqypogOU= Date: Tue, 23 Mar 2021 21:52:26 +0200 From: Laurent Pinchart To: Doug Anderson Cc: Stephen Boyd , Andrzej Hajda , Neil Armstrong , Sam Ravnborg , Jernej Skrabec , Jonas Karlman , LKML , dri-devel , Sean Paul Subject: Re: [PATCH v3 3/4] drm/bridge: ti-sn65dsi86: Read EDID blob over DDC Message-ID: References: <20201102181144.3469197-1-swboyd@chromium.org> <20201102181144.3469197-4-swboyd@chromium.org> <161646947526.2972785.6883720652669260316@swboyd.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Doug, On Tue, Mar 23, 2021 at 12:07:27PM -0700, Doug Anderson wrote: > On Mon, Mar 22, 2021 at 8:17 PM Stephen Boyd wrote: > > > > Quoting Laurent Pinchart (2021-03-17 17:20:43) > > > Hi Stephen, > > > > > > Reviving a bit of an old thread, for a question. > > > > > > On Mon, Nov 02, 2020 at 10:11:43AM -0800, Stephen Boyd wrote: > > > > @@ -265,6 +267,23 @@ connector_to_ti_sn_bridge(struct drm_connector *connector) > > > > static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector) > > > > { > > > > struct ti_sn_bridge *pdata = connector_to_ti_sn_bridge(connector); > > > > + struct edid *edid = pdata->edid; > > > > + int num, ret; > > > > + > > > > + if (!edid) { > > > > + pm_runtime_get_sync(pdata->dev); > > > > + edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc); > > > > + pm_runtime_put(pdata->dev); > > > > > > Is there any specific reason to use the indirect access method, compared > > > to the direct method that translates access to an I2C ancillary address > > > to an I2C-over-AUX transaction (see page 20 of SLLSEH2B) ? The direct > > > method seems it would be more efficient. > > > > No I don't think it matters. I was just using the existing support code > > that Sean wrote instead of digging into the details. Maybe Sean ran into > > something earlier and abandoned that approach? > > From reading the docs, it sounds as if there _could_ be a reason to > use the indirect method. Specifically if the i2c host that the bridge > is on doesn't support clock stretching then the direct method wouldn't > work according to the docs. Is that something that we'd have to > reasonably worry about? I'm not sure. I'm going through BSP code that uses the direct method, and I was wondering if it was just an implementation detail. Once I get the display working on this board, I'll try to find time to compare the two methods, to see if there's a significatant performance improvement from the direct method. If there isn't, I won't bother. -- Regards, Laurent Pinchart