lkml.org 
[lkml]   [2015]   [Sep]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] ARM: exynos_defconfig: Disable simplefb support
From
Date
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 <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>
>

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


\
 
 \ /
  Last update: 2015-09-11 10:01    [W:0.062 / U:0.208 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site