From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751823AbbIKHku (ORCPT ); Fri, 11 Sep 2015 03:40:50 -0400 Received: from lists.s-osg.org ([54.187.51.154]:35587 "EHLO lists.s-osg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751484AbbIKHks (ORCPT ); Fri, 11 Sep 2015 03:40:48 -0400 Subject: Re: [PATCH] ARM: exynos_defconfig: Disable simplefb support To: Krzysztof Kozlowski , linux-kernel@vger.kernel.org References: <1441892552-13819-1-git-send-email-javier@osg.samsung.com> <55F26042.2080600@samsung.com> <55F27D9F.1000702@osg.samsung.com> <55F27FB1.50100@samsung.com> Cc: Michael Turquette , Kukjin Kim , Thierry Reding , Anand Moon , Russell King , linux-samsung-soc@vger.kernel.org, Lukasz Majewski , linux-arm-kernel@lists.infradead.org From: Javier Martinez Canillas X-Enigmail-Draft-Status: N1110 Message-ID: <55F2857B.4020800@osg.samsung.com> Date: Fri, 11 Sep 2015 09:40:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 MIME-Version: 1.0 In-Reply-To: <55F27FB1.50100@samsung.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Krzysztof, On 09/11/2015 09:16 AM, Krzysztof Kozlowski wrote: > On 11.09.2015 16:07, Javier Martinez Canillas wrote: >> Hello Krzysztof, >> >> On 09/11/2015 07:01 AM, Krzysztof Kozlowski wrote: >>> On 10.09.2015 22:42, Javier Martinez Canillas wrote: >>>> The simplefb driver allows the kernel to render on a pre-allocated >>>> buffer that's been initialized by firmware before the kernel boots. >>>> >>>> This option was enabled to have display working on the Exynos5250 >>>> Snow Chromebook by commit da9d0fbf5e9a ("ARM: exynos: defconfig >>>> update") since proper DRM/KMS support did not exist at that time. >>>> >>>> But now that the Exynos DRM driver has support for this hardware, >>>> there is no need to have simplefb enabled. In fact, if a user has >>>> a u-boot that injects the simplefb dev node to the FDT before pass >>>> it to the kernel, display won't be properly initialized and only a >>>> blank screen will be shown since there isn't a proper handoff from >>>> the simplefb driver to the Exynos DRM driver. >>>> >>>> Signed-off-by: Javier Martinez Canillas >>>> >>>> --- >>>> >>>> arch/arm/configs/exynos_defconfig | 1 - >>>> 1 file changed, 1 deletion(-) >>> >>> Seems logical. None of the boards use simple-framebuffer compatible >>> anyway. I understand that on Snow simplefb was needed along with change >>> in Uboot like this one: >>> https://chromium.googlesource.com/chromiumos/third_party/u-boot/+/refs/changes/58/49358/2 >>> >> >> Exactly but you won't see the dev node with the "simple-framebuffer" >> compatible string in the DTS since is the bootloader that adds this >> device node to the FDT before passing it to the kernel. >> >> The bootloader shouldn't mangle the FDT (with the exception of the >> memory and choosen/bootargs nodes) but simplefb is just a hack to >> re-use the display HW initialization made by the bootloader. >> >>> and now none of Exynos boards use simplefb anymore? >>> >> >> Yes, there are no other Exynos boards using simplefb besides Snow >> that I'm aware of but since Exynos DRM is working well on this board >> from v4.0, there is no need for it anymore. > > OK, > Reviewed-by: Krzysztof Kozlowski > Thanks! >> >> In fact, as explained in the commit message, it could do more harm >> than good since users that are still booting with a u-boot that adds >> the simplefb device node, only get a blank screen since the simplefb >> driver is probed, creates a console and later the Exynos DRM probes >> and re-initializes the HW creating its own console, causing this issue. >> >> I got several reports of users that says that mainline stop booting for >> them but is just that they didn't get display working. Disabling simplefb >> makes display to work again so maybe this is even -rc material and should >> go to stable # v4.0+ > > You know, it is only a defconfig. The issue is there regardless of > change in defconfig. I am not convinced that defconfig problems are > worth backporting. multi_v7 has it enabled anyway. > Yes, that's why I said "maybe" :) > Maybe the EXYNOS_DRM should have some anti-dependency on SIMPLE_FB? But hrmm I don't know, I think this issue happens with any DRM driver. Hopefully there should be soon a nice hand off from simplefb to DRM drivers like early console does to the real console drivers for UARTs. > on the other hand the issue is actually caused by hacks in bootloader... > Yeah and in fact this does not happen with the stock bootloader that comes shipped on these devices, is with a special build that has this hack enabled. > > Best regards, > Krzysztof > > Thanks a lot for your feedback. Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America