[RFC 1/1] board: sifive: unmatched: use zero copy for initrd

[Tom Rini]

On Mon, Jul 19, 2021 at 11:52:09PM +0200, Heinrich Schuchardt wrote:
> 
> 
> On 19.07.21 23:38, Heinrich Schuchardt wrote:
> > Booting Ubuntu Impish showed the following output:
> > 
> >      relocaddr   = 0x00000000fff60000
> > 
> >      Loading Ramdisk to fa118000, end fffff19d ...
> > 
> > The initrd is overwriting the U-Boot binary. Booting fails.
> > 
> > There is no need to copy the initrd from $ramdisk_addr_r.
> > Set init_high = ~0UL to use zero copy.
> > 
> > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> > ---
> > Generally copying to another memory location than $ramdisk_addr_r provides
> > no benefit whatsoever.
> > 
> > But we still should find out why the initrd relocation fails so badly.
> > ---
> >   include/configs/sifive-unmatched.h | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/include/configs/sifive-unmatched.h b/include/configs/sifive-unmatched.h
> > index d63a5f62fb..8dcfffedbe 100644
> > --- a/include/configs/sifive-unmatched.h
> > +++ b/include/configs/sifive-unmatched.h
> > @@ -67,6 +67,7 @@
> >   	"scriptaddr=0x88100000\0" \
> >   	"pxefile_addr_r=0x88200000\0" \
> >   	"ramdisk_addr_r=0x88300000\0" \
> > +	"initrd_high=0xffffffffffffffff\0" \
> >   	"kernel_comp_addr_r=0x90000000\0" \
> 
> Tom remarked that kernel_comp_addr_r is poorly chosen as it will overlap
> with initrd if initrd exceeds 125 MiB. Current RISC-V Linux thinks
> initrd should fit into the first 128 MiB of RAM but that is an
> unnecessary restriction in Linux.

I'll repeat what I said on IRC as well.  I lament that there does not
seem to be as detailed "booting" requirements in Linux for RISC-V as
there is for arm/aarch64 because we REALLY need something like:
https://source.denx.de/u-boot/u-boot/-/blob/master/include/configs/ti_armv7_common.h#L32
but for one or more RISC-V platforms (and well, MIPS and everyone else
using device trees) that can be referenced when bringing up a new board
to get good and always safe addresses to use.

And I'll even say now that the ti_armv7_common.h example could be
improved upon because I'm not super thrilled with the DTBO storage spot,
but I don't have a better answer off the top of my head.

-- 
Tom
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