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

[Walter Lozano <walter.lozano@collabora.com>]

On 7/17/24 12:44, Tom Rini wrote:
> On Wed, Jul 17, 2024 at 11:59:50AM +0100, Peter Robinson wrote:
>> On Tue, 16 Jul 2024 at 18:21, Tom Rini <trini@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@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.
> 
> OK, that should be enough to put a 128MiB spot for kernel, then 512KiB
> for device tree, and then rest for initrd, and not be disabling
> relocation (and thus preventing U-Boot from fixing failures).
> 

Thanks for the feedback! If I understood it correctly a layout like the
the one bellow would be the right thing. The only difference is in
device tree for which is reserved a bit more.

pxefile_addr_r=0x00080000
scriptaddr=0x00100000
kernel_addr_r=0x00200000
fdt_addr_r=0x09800000
ramdisk_addr_r=0x09900000

If this matches the expectations I will prepare the V2.

Thanks in advance,

Walter

-- 
Walter Lozano
Collabora Ltd.