[PATCH] board: rpi: Update memory layout for Aarch64

[Peter Robinson]

On Tue, 16 Jul 2024 at 18:21, Tom Rini <trini at konsulko.com> wrote:
>
> On Tue, Jul 16, 2024 at 02:16:02PM -0300, Walter Lozano wrote:
>
> > ARM and Aarch64 have different restrictions and trying to accommodate
> > larger kernels like the ones used in distros can be challenging. For this
> > reason, separate the layout and rearrange the map for Aarch64 to support
> > kernels larger than 36 MB.
> >
> > Signed-off-by: Walter Lozano <walter.lozano at collabora.com>
> > ---
> >
> >  board/raspberrypi/rpi/rpi.env | 25 ++++++++++++++++++-------
> >  1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/board/raspberrypi/rpi/rpi.env b/board/raspberrypi/rpi/rpi.env
> > index 30228285edd..37c7f6a920e 100644
> > --- a/board/raspberrypi/rpi/rpi.env
> > +++ b/board/raspberrypi/rpi/rpi.env
> > @@ -42,13 +42,19 @@ dfu_alt_info+=zImage fat 0 1
> >   *   For Aarch64, the kernel image is uncompressed and must be loaded at
> >   *   text_offset bytes (specified in the header of the Image) into a 2MB
> >   *   boundary. The 'booti' command relocates the image if necessary. Linux uses
> > - *   a default text_offset of 0x80000.  In summary, loading at 0x80000
> > - *   satisfies all these constraints and reserving memory up to 0x02400000
> > - *   permits fairly large (roughly 36M) kernels.
> > + *   a default text_offset of 0x80000.  However, loading it at 0x80000
> > + *   will allow to reserve only up to 0x02400000 which permits medium size
> > + *   kernels (roughly 36M). This is good enough for customized kernels but
> > + *   not for distros which by default enable drivers for many different
> > + *   boards. Under these circumstances, using 0x00200000 provides room for
> > + *   larger kernels.
> >   *
> >   * scriptaddr and pxefile_addr_r can be pretty much anywhere that doesn't
> >   * conflict with something else. Reserving 1M for each of them at
> > - * 0x02400000-0x02500000 and 0x02500000-0x02600000 should be plenty.
> > + * 0x02400000-0x02500000 and 0x02500000-0x02600000 should be plenty for ARM.
> > + *
> > + *   For Aarch64, since the kernel is placed in different location,
> > + *   accommodate them to reserver 1M for each of them.
> >   *
> >   * On ARM, both the DTB and any possible initrd must be loaded such that they
> >   * fit inside the lowmem mapping in Linux. In practice, this usually means not
> > @@ -62,16 +68,21 @@ dfu_alt_info+=zImage fat 0 1
> >   * large initrds before they start colliding with U-Boot.
> >   */
> >  #ifdef CONFIG_ARM64
> > +pxefile_addr_r=0x00080000
> > +scriptaddr=0x00100000
> > +kernel_addr_r=0x00200000
> > +fdt_addr_r=0x03400000
> > +ramdisk_addr_r=0x03500000
> >  fdt_high=ffffffffffffffff
> >  initrd_high=ffffffffffffffff
> >  #else
> > -fdt_high=ffffffff
> > -initrd_high=ffffffff
> > -#endif
> >  kernel_addr_r=0x00080000
> >  scriptaddr=0x02400000
> >  pxefile_addr_r=0x02500000
> >  fdt_addr_r=0x02600000
> >  ramdisk_addr_r=0x02700000
> > +fdt_high=ffffffff
> > +initrd_high=ffffffff
> > +#endif
> >
> >  boot_targets=mmc usb pxe dhcp
>
> We need to drop the disabling of device tree / initrd relocation as
> that's sure not going to help matters. What's the minimum amount of
> memory an aarch64 Pi will have? I really prefer reserving 128MiB (even
> if that's not the maximum Linux Kernel Image size anymore) and then
> device tree and then initrd.

512Mb on the Zero2W and RPi3A.

We've not seen an issue here on the very large Fedora kernel, but I
suspect that's because using UEFI mitigates this somewhat because here
we're actually loading shim/grub.

Peter