linux-kernel - Re: [Arm-netbook] getting allwinner SoC support upstream (was Re: Uploading linux (3.9.4-1))

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Date:	Wed, 5 Jun 2013 19:28:42 -0400
From:	"jonsmirl@...il.com" <jonsmirl@...il.com>
To:	"luke.leighton" <luke.leighton@...il.com>
Cc:	Linux on small ARM machines <arm-netbook@...ts.phcomp.co.uk>,
	devicetree-discuss <devicetree-discuss@...abs.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	debian-arm@...ts.debian.org,
	ARM Linux Mailing List <linux-arm-kernel@...ts.infradead.org>,
	debian-kernel@...ts.debian.org
Subject: Re: [Arm-netbook] getting allwinner SoC support upstream (was Re:
 Uploading linux (3.9.4-1))

On Wed, Jun 5, 2013 at 7:26 PM, luke.leighton <luke.leighton@...il.com> wrote:
> On Thu, Jun 6, 2013 at 12:07 AM, jonsmirl@...il.com <jonsmirl@...il.com> wrote:
>> On Wed, Jun 5, 2013 at 6:47 PM, luke.leighton <luke.leighton@...il.com> wrote:
>>> On Wed, Jun 5, 2013 at 10:59 PM, Henrik Nordström
>>> <henrik@...riknordstrom.net> wrote:
>>>
>>>>>  .... and then there's the boot0 and boot1 loaders, these *do* have
>>>
>>>> no, these are not tiny. boot0 is 24KB to fit the initial embedded SRAM
>>>> (not cache), but boot1 is on pair with u-boot in size and runs from
>>>> DRAM.
>>>
>>>  btw, please listen to henrik: he knows what he's talking about, as
>>> you can see :)   henrik, thank you for correcting my technical
>>> misunderstandings, i'll try to remember them and not propagate
>>> incorrect stuff.
>>
>> This is not about the fex syntax or uboot. The root problem is needing
>> two sets of binding for every device driver in the kernel. Pick a
>> random driver like gpio-pca953x.c and look at the source. In that file
>> there are #ifdef CONFIG_OF_ sections. Those sections are directly
>> reading the FDT binary via calls like of_get_property(node,
>> "linux,gpio-base", &size);. If fex is added to the kernel every driver
>> driver will now need both a #ifdef CONFIG_OF_ section and also a
>> #ifdef CONFIG_FEX_ section. Doing that is just crazy.
>
>  yes.  which is why they haven't done it.
>
>> Is Allwinner
>> going to add fex support to every single device driver in the kernel?
>
>  no john - they've only added it to the multiplexed sections of the
> drivers which they themselves have written.  such as
> drivers/usb/sun{N}i_usb/*.[ch], drivers/block/nand/sun{N}_i,
> arch/arm/mach-sun{N}i and so on.
>
> even the touchscreen driver that they wrote, that's got nothing to do
> with any other code in the touchscreen linux kernel source tree: it's
> more of a "meta-"driver which even has the name of the linux kernel
> module that needs to be loaded and what I2C address, GPIO options etc.
> to pass in [normally done as modprobe options in userspace].
>
>  to be honest, there are better people to fully answer this question
> (alejandro and henrik are two that spring to mind) but you're
> definitely off-base, jon.  the script.fex system deals with the pinmux
> issue in a very neat way that:
>
>   a) has very little impact on the rest of the kernel tree [citation
> needed!  i'm saying that: could someone please confirm if it's true]
>
>   b) the linux kernel developers could, instead of criticising it,
> actually learn a great deal from.
>
> l.



-- 
Jon Smirl
jonsmirl@...il.com
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