Messages in this thread | | | Subject | Re: [PATCH] ARM: exynos_defconfig: Disable simplefb support | From | Krzysztof Kozlowski <> | Date | Fri, 11 Sep 2015 16:16:01 +0900 |
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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 <javier@osg.samsung.com> >>> >>> --- >>> >>> 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 <k.kozlowski@samsung.com>
> > 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
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