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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 78D27ECE58E for ; Thu, 17 Oct 2019 11:41:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4C12B20659 for ; Thu, 17 Oct 2019 11:41:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="hexeKemy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409212AbfJQLlw (ORCPT ); Thu, 17 Oct 2019 07:41:52 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:45290 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727991AbfJQLlv (ORCPT ); Thu, 17 Oct 2019 07:41:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender: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-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=r+Q3LUtMArQNVtEuVWYwd/gVihapefhZ4NaqVNvBt2E=; b=hexeKemyFMqhlYKddx44XfooO ELtD5P6CikyQA/uPSMsgDh168xhS/ZGfZvsdYe7ejUlXCHqn7hiTgMvxQbnIevboyZYnmCSL8rNP7 RNGfR6bpNVk3icaqReknuHl10R8mNZ2v9s2jNECTJFBfIkWH/jNYUt5ViLHw24S01p04vjk6mkKXC 9BwGEu4KoL4GH3HChYbLvEHagxKu0q4HjrD1iDMuGcs776AS1B4DouVgKnPxRATkTnzoayqU+U3sA 0tW2a5I1vMgIu+bl7wVgBUpLFtCI+dhGb+omZ6ZVmjFEf74WYwYZ2LV5iYa9Pl/DSlmz/ZEzugQyA dcZqZbeMw==; Received: from shell.armlinux.org.uk ([2001:4d48:ad52:3201:5054:ff:fe00:4ec]:43854) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1iL4A1-0000Ck-IQ; Thu, 17 Oct 2019 12:41:41 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1iL49x-0008As-Nc; Thu, 17 Oct 2019 12:41:37 +0100 Date: Thu, 17 Oct 2019 12:41:37 +0100 From: Russell King - ARM Linux admin To: Brian Starkey Cc: "james qian wang (Arm Technology China)" , Mihail Atanassov , "dri-devel@lists.freedesktop.org" , David Airlie , Liviu Dudau , Maxime Ripard , "linux-kernel@vger.kernel.org" , nd , Sean Paul Subject: Re: [RFC,3/3] drm/komeda: Allow non-component drm_bridge only endpoints Message-ID: <20191017114137.GC25745@shell.armlinux.org.uk> References: <20191004143418.53039-4-mihail.atanassov@arm.com> <20191009055407.GA3082@jamwan02-TSP300> <5390495.Gzyn2rW8Nj@e123338-lin> <20191016162206.u2yo37rtqwou4oep@DESKTOP-E1NTVVP.localdomain> <20191017030752.GA3109@jamwan02-TSP300> <20191017082043.bpiuvfr3r4jngxtu@DESKTOP-E1NTVVP.localdomain> <20191017102055.GA8308@jamwan02-TSP300> <20191017104812.6qpuzoh5bx5i2y3m@DESKTOP-E1NTVVP.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191017104812.6qpuzoh5bx5i2y3m@DESKTOP-E1NTVVP.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 17, 2019 at 10:48:12AM +0000, Brian Starkey wrote: > On Thu, Oct 17, 2019 at 10:21:03AM +0000, james qian wang (Arm Technology China) wrote: > > On Thu, Oct 17, 2019 at 08:20:56AM +0000, Brian Starkey wrote: > > > On Thu, Oct 17, 2019 at 03:07:59AM +0000, james qian wang (Arm Technology China) wrote: > > > > On Wed, Oct 16, 2019 at 04:22:07PM +0000, Brian Starkey wrote: > > > > > > > > > > If James is strongly against merging this, maybe we just swap > > > > > wholesale to bridge? But for me, the pragmatic approach would be this > > > > > stop-gap. > > > > > > > > > > > > > This is a good idea, and I vote +ULONG_MAX :) > > > > > > > > and I also checked tda998x driver, it supports bridge. so swap the > > > > wholesale to brige is perfect. :) > > > > > > > > > > Well, as Mihail wrote, it's definitely not perfect. > > > > > > Today, if you rmmod tda998x with the DPU driver still loaded, > > > everything will be unbound gracefully. > > > > > > If we swap to bridge, then rmmod'ing tda998x (or any other bridge > > > driver the DPU is using) with the DPU driver still loaded will result > > > in a crash. > > > > I haven't read the bridge code, but seems this is a bug of drm_bridge, > > since if the bridge is still in using by others, the rmmod should fail > > > > Correct, but there's no fix for that today. You can also take a look > at the thread linked from Mihail's cover letter. > > > And personally opinion, if the bridge doesn't handle the dependence. > > for us: > > > > - add such support to bridge > > That would certainly be helpful. I don't know if there's consensus on > how to do that. > > > or > > - just do the insmod/rmmod in correct order. > > > > > So, there really are proper benefits to sticking with the component > > > code for tda998x, which is why I'd like to understand why you're so > > > against this patch? > > > > > > > This change handles two different connectors in komeda internally, compare > > with one interface, it increases the complexity, more risk of bug and more > > cost of maintainance. > > > > Well, it's only about how to bind the drivers - two different methods > of binding, not two different connectors. I would argue that carrying > our out-of-tree patches to support both platforms is a larger > maintenance burden. > > Honestly this looks like a win-win to me. We get the superior approach > when its supported, and still get to support bridges which are more > common. > > As/when improvements are made to the bridge code we can remove the > component bits and not lose anything. There was an idea a while back about using the device links code to solve the bridge issue - but at the time the device links code wasn't up to the job. I think that's been resolved now, but I haven't been able to confirm it. I did propose some patches for bridge at the time but they probably need updating. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up