From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751490AbbIKHHT (ORCPT ); Fri, 11 Sep 2015 03:07:19 -0400 Received: from lists.s-osg.org ([54.187.51.154]:35561 "EHLO lists.s-osg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751379AbbIKHHR (ORCPT ); Fri, 11 Sep 2015 03:07:17 -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> From: Javier Martinez Canillas X-Enigmail-Draft-Status: N1110 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 Message-ID: <55F27D9F.1000702@osg.samsung.com> Date: Fri, 11 Sep 2015 09:07:11 +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: <55F26042.2080600@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 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. 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+ > Best regards, > Krzysztof > > Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America