On 29/11/2023 16:34, Caleb Connolly wrote:
On 23/11/2023 07:04, Sumit Garg wrote:
On Wed, 22 Nov 2023 at 21:34, Caleb Connolly <caleb.conno...@linaro.org> wrote:
On 22/11/2023 14:27, Tom Rini wrote:
On Wed, Nov 22, 2023 at 07:44:09PM +0530, Sumit Garg wrote:
On Wed, 22 Nov 2023 at 19:31, Tom Rini <tr...@konsulko.com> wrote:
On Wed, Nov 22, 2023 at 11:51:29AM +0530, Sumit Garg wrote:
Hi Caleb,
On Tue, 21 Nov 2023 at 22:39, Caleb Connolly <caleb.conno...@linaro.org> wrote:
[snip]
== DT loading ==
Previously, boards used the FDT blob embedded into U-Boot (via
OF_SEPARATE). However, most Qualcomm boards run U-Boot as a secondary
bootloader, so we can instead rely on the first-stage bootloader to
populate some useful FDT properties for us (notably the /memory node and
KASLR seed) and fetch the DTB that it provides. Combined with the memory
map changes above, this let's us entirely avoid configuring the memory
map explicitly.
Since with this change, we don't need to embed FDT blob in the u-boot
binary, so I was thinking if we really need to import DTs from Linux
for different platforms and then play a catchup game?
For now, yes.
But why? Is there any value added by larger u-boot specific DT (most
of the nodes being unused by u-boot) than what currently u-boot
supports? The more important part is to get alignment with Linux DT
bindings. If you need to have memory/reserved-memory nodes in u-boot
DT for generalization purposes then you should import those particular
nodes only.
I've been thinking about and hacking on this for the last week or so,
sorry for the delayed reply here.
The value is in preventing any of the existing bindings from regressing,
and simplifying the bringup process for new platforms (just copy
SoC/PMIC DTSI and write a minimal board DTS to enable the needed hardware).
There are quite a few features which aren't handled by
U-Boot that it shouldn't need to handle (rpm/h resources for example).
Also the fixed-regulator / regulator-gpio binding differences.
IMO, we should fix them first and then use Linux DT as it is.
The biggest blocker here is USB, on sdm845 and the 4 new platforms I
have working, I only support USB high speed, this requires removing the
superspeed phy and adding a DTS property.
I tried using OF_BOARD_SETUP to make this changes during boot but this
approach really isn't scalable (and I couldn't find a way to make it
work anyway).
I would definitely like to move towards supporting Linux DT directly,
but this approach gives us a nice middleground of minimising the U-Boot
specific DT parts.
I don't see any real benefits here apart from the maintenance burden.
If it had been an actual Linux DT then that can be passed to Linux as
it is. However, the current modified import you are trying to do
doesn't solve that purpose as well.
Ensuring that we don't introduce non-standard bindings (by using Linux
DTSI) is one benefit, simplifying new platform bringup is another.
The amount of work required to switch to upstream DT is too much to
block this series on. We can work on improving the situation there once
we have these Qualcomm improvements upstream and new boards added. I do
admit that this is quite an awkward middle-ground, and I would not like
it to last for too long.
I'm a real supporter of targeting support of unmodified (or very slighly)
Linux DT, having a reduced version of the Linux DT will be a pain at each
sync, and you'll need to do this manually.
Simply having to copy the Linux DT without any changes will make sure you
are in sync with Linux's bindings, and will help making sure you'll boot
unchanged Linux DTBs you get from previous loaders.
And in bonus, you'll be able to chain it to the next loader like EFI.
So I don't see why any work toward this goal is useless, and if an
intermediate step is needed, let's do it.
Neil
-Sumit
IMO, the build command would look like following if we import
pre-built FDT blob from Linux:
- Build u-boot::
$ export CROSS_COMPILE=<aarch64 toolchain prefix>
$ make qcom_defconfig
$ make
- gzip u-boot::
gzip u-boot-nodtb.bin
- Append dtb to gzipped u-boot::
cat u-boot-nodtb.bin.gz
<linux-tree>/arch/arm64/boot/dts/qcom/your-board.dtb >
u-boot-nodtb.bin.gz-dtb
This would avoid the maintenance burden to keep DT in sync with that
of Linux. And since DT bindings in Linux are backwards compatible, we
can say u-boot should work with DTB picked up from any Linux kernel
stable release.
I guess one question I have is, are we being passed the device tree
(since we're acting like the Linux Kernel)
Yeah that is the case here, see patch #1 in this series regarding how
FDT address is being retrieved from previous stage bootloader (ABL on
sdm845 and qcs404 SoCs).
That's what I thought.
or knowing that we have the
dtb attached to the end of us and making use of the old kernel appended
dtb option? We're fine in for example the rpi_arm64 case of just being
given a device tree from the previous stage and not needing one in-tree.
That's good to know and we can replicate that for Qcom platforms which
are chainloaded and don't need an embedded DT.
So yes, moving these towards the direction of rpi_arm64 and specifically
using imply OF_HAS_PRIOR_STAGE or select OF_HAS_PRIOR_STAGE (force that
the dtb must be provided to us) sounds like the right direction to take
these platforms
--
// Caleb (they/them)
