[U-Boot] ATAGS for Tegra, Sunxi, etc.

[Tom Rini]

On Thu, Dec 17, 2015 at 10:26:07AM +0100, Hans de Goede wrote:
> Hi,
> 
> On 17-12-15 10:21, Ian Campbell wrote:
> >On Thu, 2015-12-17 at 07:40 +0100, Karsten Merker wrote:
> >>On Thu, Dec 17, 2015 at 01:59:57PM +0900, Masahiro Yamada wrote:
> >>>2015-12-17 13:58 GMT+09:00 Masahiro Yamada <yamada.masahiro at socionext.c
> >>>om>:
> >>>>Hi,
> >>>>
> >>>>I noticed some well-maintained new SoC families still
> >>>>define CONFIG_CMDLINE_TAG.
> >>>>
> >>>>
> >>>>For example,
> >>[...]
> >>>>include/configs/sunxi-common.h
> >>>>
> >>>>  #define CONFIG_SETUP_MEMORY_TAGS
> >>>>  #define CONFIG_CMDLINE_TAG
> >>>>  #define CONFIG_INITRD_TAG
> >>>>  #define CONFIG_SERIAL_TAG
> >>
> >>>>Do they still use ATAGS, not device tree?
> >>
> >>Sunxi uses devicetree for mainline kernels, but AFAIK ATAG
> >>support is necessary to enable booting legacy vendor kernels.
> >>There is still new sunxi-based hardware sold today that comes
> >>with legacy 3.4-based kernels.
> >
> >That legacy kernel is FEX (allwinners own description blob) based, I don't
> >know to what extent that involves ATAGs in some way though.
> >
> >There are also people who use the 3.4 based fork from linux-sunxi.org, but
> >I don't know if that is DT or ATAGS or FEX.
> >
> >A dependency on CONFIG_OLD_SUNXI_KERNEL_COMPAT might be an option depending
> >on what the kernels need, Hans probably knows better than I do.
> 
> The 3.4 based kernels use both ATAGS for things like memory size, and fex
> for other hw config info.
> 
> I'm not in favor of wrapping things in CONFIG_OLD_SUNXI_KERNEL_COMPAT, because
> recent 3.4 based kernels can boot without that, and I believe that removing
> the ATAG support will break this, without really buying us much.

+1.  ATAG is also used iirc for some other operating systems, still.

-- 
Tom
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