From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f194.google.com ([209.85.214.194]:34176 "EHLO mail-ob0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751536AbcBJRRZ (ORCPT ); Wed, 10 Feb 2016 12:17:25 -0500 Received: by mail-ob0-f194.google.com with SMTP id x5so2674487obg.1 for ; Wed, 10 Feb 2016 09:17:25 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <56BB652A.1010107@gmail.com> References: <1454894009-15466-1-git-send-email-mario.kleiner.de@gmail.com> <1454894009-15466-6-git-send-email-mario.kleiner.de@gmail.com> <20160209100917.GP11240@phenom.ffwll.local> <56B9EF5A.6050902@gmail.com> <20160209141149.GP23290@intel.com> <20160209150347.GZ11240@phenom.ffwll.local> <56BB652A.1010107@gmail.com> Date: Wed, 10 Feb 2016 18:17:25 +0100 Message-ID: Subject: Re: [PATCH 5/6] drm: Prevent vblank counter jumps with timestamp based update method. From: Daniel Vetter To: Mario Kleiner Cc: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , dri-devel , linux@bernd-steinhauser.de, stable , =?UTF-8?Q?Michel_D=C3=A4nzer?= , Vlastimil Babka , "alexander.deucher@amd.com" , =?UTF-8?Q?Christian_K=C3=B6nig?= Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: On Wed, Feb 10, 2016 at 5:28 PM, Mario Kleiner wrote: > There's another scenario where this zero-ts case can be hit. If the driver > drm_vblank_init()'s - setting all timestamps to zero - and then code starts > using vblanks (drm_vblank_get()) without drm_vblank_on beforehand, which is > afaics the case with nouveau. Unless that's considered an error as well, > we'd need to init the timestamps to something non-zero but harmless like 1 > usecs at drm_vblank_init() time? Both legacy modeset helpers and atomic ones assume by default that you start out with everything disabled. Pre-atomic drivers make that happen by calling disable_unused_functions() to shut down anything the bios has enabled. I think this can't happen. For drivers that do take over bootloader display config they must call vblank_on explicitly themselves, which i915 does. > What makes sense as output here? DRM_WARN_ONCE? I'd go with WARN_ON and tune it down if it's offensive. But WARN_ON patch for 4.6 of course. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch