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 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 DDF6FC433F5 for ; Tue, 14 Sep 2021 16:27:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C0EE260FD7 for ; Tue, 14 Sep 2021 16:27:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229492AbhINQ22 (ORCPT ); Tue, 14 Sep 2021 12:28:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:35626 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229551AbhINQ22 (ORCPT ); Tue, 14 Sep 2021 12:28:28 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 53129610A6; Tue, 14 Sep 2021 16:27:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631636830; bh=aigduJq2CR6S4pAIzNs+46OI9RZyIvH6L534d0efEec=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=D+3HD0ml++Tx8+/VNtLtnxCU0+Tdl7DEFFUyyte/BUXQzbdPKe+XOaQTA1TDfxfQ9 XXv/R4LeNt6O6jKL4HUk3l6TnrKJkUn0ZiFrtRiyfjQOQORsLiK/zhBexYqlrgBo+c NFf/S9/s6qSVfoLEvx2f1xNgK5LI3Im0YbBR5Mio= Date: Tue, 14 Sep 2021 18:27:08 +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: stable@vger.kernel.org On Mon, Sep 13, 2021 at 09:31:03AM -0700, Doug Anderson wrote: > Hi, > > On Mon, Sep 13, 2021 at 9:09 AM Greg Kroah-Hartman > wrote: > > > > 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? > > It's been a long journey trying to make this bridge work better. I > think the easiest way to say it is that if you don't have the parent > of ${SUBJECT} patch, AKA: > > e0bbcc6233f7 drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus > > ...then you don't have DP AUX bus support and you shouldn't take > ${SUBJECT} patch. If you have that patch and it compiles / builds then > it means that you have all the proper dependencies. However, there are > _a lot_ of dependencies and I wouldn't suggest picking them all to > stable unless it's critical for someone. I tried to drop this one, and it turned out to be a depandancy for another patch for this driver. And that was another dependancy. So I've now dropped all of these from the queue. Here are the commits I dropped. If you think any should be added back, please let us know: 05a7f4a8dff1 ("devlink: Break parameter notification sequence to be before/after unload/load driver") e183bf31cf0d ("drm/bridge: ti-sn65dsi86: Add some 100 us delays") c7782443a889 ("drm/bridge: ti-sn65dsi86: Avoid creating multiple connectors") a70e558c1510 ("drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC") acb06210b096 ("drm/bridge: ti-sn65dsi86: Fix power off sequence") 4c1b3d94bf63 ("drm/bridge: ti-sn65dsi86: Improve probe errors with dev_err_probe()") 4e5763f03e10 ("drm/bridge: ti-sn65dsi86: Wrap panel with panel-bridge") thanks, greg k-h