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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 CE5BCC433FE for ; Mon, 13 Sep 2021 16:09:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B1E1D60F9B for ; Mon, 13 Sep 2021 16:09:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345258AbhIMQKd (ORCPT ); Mon, 13 Sep 2021 12:10:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:44282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235546AbhIMQKc (ORCPT ); Mon, 13 Sep 2021 12:10:32 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4AE25604D1; Mon, 13 Sep 2021 16:09:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631549356; bh=MDC4CdstYZFwgRAmMGslyg8XtdsQPBHzlq8pVMP5A+A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KEf+n7YYrhGpogj+xis9XzGpEN6bMp+cNGv1jggMwXbWDtrh3g05mEJ0hpJsgowqE s/AL5gDPASImA+NLkmo8N7fDmuC5WC1YXJ/jR5FH57GmELzcyKm3rfQxJkF1B6kN08 6ObO4eZawbVZocctMAJK5JFAQ8ho5xtDGZu8YumM= Date: Mon, 13 Sep 2021 18:09:14 +0200 From: Greg Kroah-Hartman To: Doug Anderson Cc: LKML , "# 4.0+" , Andrzej Hajda , Bjorn Andersson , Sasha Levin Subject: Re: [PATCH 5.14 147/334] drm/bridge: ti-sn65dsi86: Dont read EDID blob over DDC Message-ID: References: <20210913131113.390368911@linuxfoundation.org> <20210913131118.330293390@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13, 2021 at 06:57:20AM -0700, Doug Anderson wrote: > Hi, > > On Mon, Sep 13, 2021 at 6:51 AM Greg Kroah-Hartman > wrote: > > > > From: Douglas Anderson > > > > [ Upstream commit a70e558c151043ce46a5e5999f4310e0b3551f57 ] > > > > This is really just a revert of commit 58074b08c04a ("drm/bridge: > > ti-sn65dsi86: Read EDID blob over DDC"), resolving conflicts. > > > > The old code failed to read the EDID properly in a very important > > case: before the bridge's pre_enable() was called. The way things need > > to work: > > 1. Read the EDID. > > 2. Based on the EDID, decide on video settings and pixel clock. > > 3. Enable the bridge w/ the desired settings. > > > > The way things were working: > > 1. Try to read the EDID but fail; fall back to hardcoded values. > > 2. Based on hardcoded values, decide on video settings and pixel clock. > > 3. Enable the bridge w/ the desired settings. > > 4. Try again to read the EDID, it works now! > > 5. Realize that the hardcoded settings weren't quite right. > > 6. Disable / reenable the bridge w/ the right settings. > > > > The reasons for the failures were twofold: > > a) Since we never ran the bridge chip's pre-enable then we never set > > the bit to ignore HPD. This meant the bridge chip didn't even _try_ > > to go out on the bus and communicate with the panel. > > b) Even if we fixed things to ignore HPD, the EDID still wouldn't read > > if the panel wasn't on. > > > > Instead of reverting the code, we could fix it to set the HPD bit and > > also power on the panel. However, it also works nicely to just let the > > panel code read the EDID. Now that we've split the driver up we can > > expose the DDC AUX channel bus to the panel node. The panel can take > > charge of reading the EDID. > > > > NOTE: in order for things to work, anyone that needs to read the EDID > > will need to instantiate their panel using the new DP AUX bus (AKA by > > listing their panel under the "aux-bus" node of the bridge chip in the > > device tree). > > > > In the future if we want to use the bridge chip to provide a full > > external DP port (which won't have a panel) then we will have to > > conditinally add EDID reading back in. > > > > Suggested-by: Andrzej Hajda > > Signed-off-by: Douglas Anderson > > Reviewed-by: Bjorn Andersson > > Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.9.I9330684c25f65bb318eff57f0616500f83eac3cc@changeid > > Signed-off-by: Sasha Levin > > --- > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 22 ---------------------- > > 1 file changed, 22 deletions(-) > > I guess it's not a huge deal, but I did respond to Sasha and request > that this patch be dropped from the stable queue unless the whole big > pile of patches was being backported. See: > > https://lore.kernel.org/lkml/CAD=FV=U2dGjeEzp+K1vnLTj8oPJ-GKBTTKz2XQ1OZ7QF_sTHuw@mail.gmail.com/ > > I said: > > > I would suggest against backporting this one unless you're going to > > backport the whole pile of DP AUX bus patches, which probably doesn't > > make sense for stable. Even though the old EDID reading was broken for > > the first read, it still worked for later reads. ...and the first read > . didn't crash or anything--it just timed out. I see a "bunch" of patches for this driver in this -rc, did Sasha not get them all? If not, I can drop this one, but maybe it was needed for the follow-on patches? thanks, greg k-h