[PATCH 2/2] arc770: move arc patches to taregt/linux/generic

[Vineet Gupta]

+CC Thomas, Peter

On Friday 15 January 2016 04:19 PM, Alexey Brodkin wrote:
> Hi Felix,
>
> On Fri, 2016-01-15 at 11:45 +0100, Felix Fietkau wrote:
>> On 2016-01-15 00:12, Alexey Brodkin wrote:
>>> Given those patches are relevant to any ARC platform and even
>>> ISA version it makes perfect sense for patches to exist
>>> in one place instead of being duplicated for each new ARC-based ASIC.
>>>
>>> Note this is a prerequisite for upstreaming of ARC HS38 support in
>>> OpenWRT.
>>>
>>> Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
>>> Cc: Felix Fietkau <nbd at openwrt.org>
>>> Cc: Jo-Philipp Wich <jow at openwrt.org>
>>> Cc: Jonas Gorski <jogo at openwrt.org>
>>> --- /dev/null
>>> +++ b/target/linux/generic/patches-4.4/331-arc-remove-dependency-on-DEVTMPFS.patch
>>> @@ -0,0 +1,36 @@
>>> +From adfbf9e6cad93281cffceab078e7f6f2a8e094f9 Mon Sep 17 00:00:00 2001
>>> +From: Alexey Brodkin <abrodkin at synopsys.com>
>>> +Date: Thu, 13 Aug 2015 01:56:02 +0300
>>> +Subject: [PATCH 1/2] openwrt: arc - remove dependency on DEVTMPFS
>>> +
>>> +OpenWRT builds initramfs so that it doesn't require DEVTMPFS so dropping
>>> +this dependency. 

Really ? AFAIKR (circa 2012) DEVTMPFS was *needed* for dynamic device nodes and
that included the common case of initramfs NOT having static device nodes.

So back then I added the code in question to kernel Kconfig because initramfs was
my primary workflow and occassionally I would fail to include DEVTMPFS causing
userspace boot to go bonkers (FWIW I was using the buildroot trick of a pre-init
script which would automount devtmpfs before exec'ing the real init)

Now arguably I can add DEVTMPFS to defconfigs, but then we don't need the kconfig
dependency framework at all.

Another idea is to add DEVTMPFS unconditionally to Kconfig, but I fail to remember
why I didn't do it at the time. Does anyone know if it interferes with real rootfs
backed by real devices ?

>>> That helps to escape 2 separate kernel rebuilds with
>>> +and without initramfs.
>>> +
>>> +2 builds happen because OpenWRT first builds kernel and later modules.
>>> +When building entire kernel with simple "make" INITRAMFS sets to a real
>>> +value and so was triggering DEVTMPFS selection. Then when building only
>>> +modules with "make modules" command INITRAMFS is zeroed and so kernel
>>> +config was changing that lead to full kernel rebuild.

Just curious, why does make module zero out INITRAMFS - to save a bit of build time ?

-Vineet

>>> +
>>> +Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
>>> +---
>>> + arch/arc/Kconfig | 2 --
>>> + 1 file changed, 2 deletions(-)
>>> +
>>> +diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
>>> +index 6312f60..a95bab3 100644
>>> +--- a/arch/arc/Kconfig
>>> ++++ b/arch/arc/Kconfig
>>> +@@ -12,8 +12,6 @@ config ARC
>>> + 	select BUILDTIME_EXTABLE_SORT
>>> + 	select COMMON_CLK
>>> + 	select CLONE_BACKWARDS
>>> +-	# ARC Busybox based initramfs absolutely relies on DEVTMPFS for /dev
>>> +-	select DEVTMPFS if !INITRAMFS_SOURCE=""
>>> + 	select GENERIC_ATOMIC64
>>> + 	select GENERIC_CLOCKEVENTS
>>> + 	select GENERIC_FIND_FIRST_BIT
>> Could you please send this one upstream as well?
> Adding Vineet so he may comment if that change makes sense upstream.
>
> -Alexey