From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751532AbbIKHQF (ORCPT ); Fri, 11 Sep 2015 03:16:05 -0400 Received: from mailout3.w1.samsung.com ([210.118.77.13]:23827 "EHLO mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751115AbbIKHQD (ORCPT ); Fri, 11 Sep 2015 03:16:03 -0400 X-AuditID: cbfec7f5-f794b6d000001495-57-55f27fb0510d Subject: Re: [PATCH] ARM: exynos_defconfig: Disable simplefb support To: Javier Martinez Canillas , 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> 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: Krzysztof Kozlowski Message-id: <55F27FB1.50100@samsung.com> Date: Fri, 11 Sep 2015 16:16:01 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-version: 1.0 In-reply-to: <55F27D9F.1000702@osg.samsung.com> Content-type: text/plain; charset=windows-1252 Content-transfer-encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrLLMWRmVeSWpSXmKPExsVy+t/xa7ob6j+FGvSu1bR483YNk8XrF4YW /Y9fM1u8ebiZ0WLT42usFpd3zWGzmHF+H5PFuo232C1uX+a1uHjK1eL2bz4Hbo+W5h42j/c3 Wtk9ds66y+6xaVUnm8fmJfUevc3v2Dy29AOF+rasYvT4vEkugDOKyyYlNSezLLVI3y6BK+Pg n2NsBeclKu7MMGlgfCfcxcjJISFgItE89SA7hC0mceHeerYuRi4OIYGljBI/P59mh3C+MEoc njGXpYuRg0NYwEVi7RQNkAYRgVCJfxdvM0LUdDFK7J+5lxXEYRbYziTx6/Q3JpAqNgFjic3L l7CB2LwCGhJ7H5wCi7MIqEps7e1kBbFFBSIkTp19C1UjKPFj8j0WEJtTQF/i14ouJpDFzAJ6 EvcvaoGEmQXkJTavecs8gVFgFpKOWQhVs5BULWBkXsUomlqaXFCclJ5rpFecmFtcmpeul5yf u4kREilfdzAuPWZ1iFGAg1GJh9dC9VOoEGtiWXFl7iFGCQ5mJRFeAzmgEG9KYmVValF+fFFp TmrxIUZpDhYlcd6Zu96HCAmkJ5akZqemFqQWwWSZODilGhhPpLS91Jx56OnSi0eFrlue/MQ1 6W+Erfed1cdvi4QvCNh1SLXmtn5+eMbt80xh0T35havSRFPVF+jwCXRnm7s/n7Sh+v32mwJ3 dirGi04rYu0St2rUOKb718LzWbbIbv4DVhwzVsUUewt4ZE0t3/VQRyydf157u8tP2x0SZz6m H3AIN9CalaDEUpyRaKjFXFScCACiujg1kAIAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > 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. Maybe the EXYNOS_DRM should have some anti-dependency on SIMPLE_FB? But on the other hand the issue is actually caused by hacks in bootloader... Best regards, Krzysztof