[RFC PATCH] arm64: defconfig: add config fragment for Freescale SoCs

[Stuart Yoder]

> -----Original Message-----
> From: Catalin Marinas [mailto:catalin.marinas at arm.com]
> Sent: Thursday, April 14, 2016 12:05 PM
> To: Stuart Yoder <stuart.yoder at nxp.com>
> Cc: linux-arm-kernel at lists.infradead.org; will.deacon at arm.com; marc.zyngier at arm.com;
> mark.rutland at arm.com; Scott Wood <scott.wood at nxp.com>; Yang-Leo Li <leoyang.li at nxp.com>
> Subject: Re: [RFC PATCH] arm64: defconfig: add config fragment for Freescale SoCs
> 
> On Thu, Apr 14, 2016 at 09:21:25AM -0500, Stuart Yoder wrote:
> > Add a config fragment enabling a reasonably useful set of
> > devices and options for Freescale ARM v8 SoCs.
> 
> A gentle NAK ;).
> 
> > I realize that we are trying to avoid the defconfig hell in arch/arm with 100+
> > defconfigs, but the single defconfig in arch/arm64 has some problems too.
> 
> Can we address these problems in defconfig?
> 
> > I think what we want with arch/arm64/config are some reasonable in-kernel
> > defconfigs/fragments with built-in drivers for convenience.
> 
> A hard requirement for arm64 is single Image and having all SoCs in
> defconfig is a good way to regularly test this.
> 
> I am aware that at some point the defconfig size will get too big but
> that's when (ideally before) we should put effort into building more
> stuff as loadable modules.
> 
> > The proposal is to allow a chip vendor 1 vendor-specific kconfig fragment
> > to cover all their chips, allowing them to _override_ the default config
> > options in defconfig.  One specific issue we have is that due to the ls2080a
> > physical address map, the combination of 4KB pages and 39-bit VA does not
> > allow us to see all our DDR.  And, thus we need CONFIG_ARM64_VA_BITS_48=y.
> 
> And I'm fine to add this to defconfig. We had a case for Seattle needing
> 48-bit VA but we eventually decoupled the number of levels for idmap and
> swapper. If it can't be addressed in a similar way on ls2080a, we may
> need to increase the VA space to 48-bit.

The issue for us is the linear mapping covering the 2 very discontiguous
memory regions on the ls2080a.  We've tried some experiments to locate all
DDR high, but that results in issues for some devices with 32-bit DMA masks,
that need bounce buffers.

I'll submit a patch to increase the VA space to 48-bit, along with 
the other options.

Thanks,
Stuart