On Mon, 4 Jul 2022 13:44:18 -0500
Samuel Holland [off-list ref] wrote:

Hi Samuel,

On 7/4/22 8:30 AM, Andre Przywara wrote:

quoted

On Sat, 02 Jul 2022 23:16:53 +0200
Jernej Škrabec [off-list ref] wrote:  

quoted

Dne četrtek, 30. junij 2022 ob 02:04:10 CEST je Andre Przywara napisal(a):  

quoted

On Tue, 03 May 2022 21:05:11 +0200
Jernej Škrabec [off-list ref] wrote:  

quoted

Dne petek, 29. april 2022 ob 01:09:30 CEST je Andre Przywara napisal(a):    

quoted

This (relatively) new SoC is similar to the H6, but drops the (broken)
PCIe support and the USB 3.0 controller. It also gets the management
controller removed, which in turn removes *some*, but not all of the
devices formerly dedicated to the ARISC (CPUS).
And while there is still the extra sunxi interrupt controller, the
package lacks the corresponding NMI pin, so no interrupts for the PMIC.

The reserved memory node is actually handled by Trusted Firmware now,
but U-Boot fails to propagate this to a separately loaded DTB, so we
keep it in here for now, until U-Boot learns to do this properly.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---

 .../arm64/boot/dts/allwinner/sun50i-h616.dtsi | 574 ++++++++++++++++++
 1 file changed, 574 insertions(+)
 create mode 100644 arch/arm64/boot/dts/allwinner/sun50i-h616.dtsi

diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h616.dtsi

b/arch/arm64/    

boot/dts/allwinner/sun50i-h616.dtsi
    

quoted

new file mode 100644
index 000000000000..cc06cdd15ba5

--- /dev/null
+++ b/arch/arm64/boot/dts/allwinner/sun50i-h616.dtsi

@@ -0,0 +1,574 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+// Copyright (C) 2020 Arm Ltd.
+// based on the H6 dtsi, which is:
+//   Copyright (C) 2017 Icenowy Zheng <icenowy@aosc.io>
+
+#include <dt-bindings/interrupt-controller/arm-gic.h>
+#include <dt-bindings/clock/sun50i-h616-ccu.h>
+#include <dt-bindings/clock/sun50i-h6-r-ccu.h>
+#include <dt-bindings/reset/sun50i-h616-ccu.h>
+#include <dt-bindings/reset/sun50i-h6-r-ccu.h>
+
+/ {
+	interrupt-parent = <&gic>;
+	#address-cells = <2>;
+	#size-cells = <2>;
+
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		cpu0: cpu@0 {
+			compatible = "arm,cortex-a53";
+			device_type = "cpu";
+			reg = <0>;
+			enable-method = "psci";
+			clocks = <&ccu CLK_CPUX>;
+		};
+
+		cpu1: cpu@1 {
+			compatible = "arm,cortex-a53";
+			device_type = "cpu";
+			reg = <1>;
+			enable-method = "psci";
+			clocks = <&ccu CLK_CPUX>;
+		};
+
+		cpu2: cpu@2 {
+			compatible = "arm,cortex-a53";
+			device_type = "cpu";
+			reg = <2>;
+			enable-method = "psci";
+			clocks = <&ccu CLK_CPUX>;
+		};
+
+		cpu3: cpu@3 {
+			compatible = "arm,cortex-a53";
+			device_type = "cpu";
+			reg = <3>;
+			enable-method = "psci";
+			clocks = <&ccu CLK_CPUX>;
+		};
+	};
+
+	reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+
+		/* 512KiB reserved for ARM Trusted Firmware (BL31) */
+		secmon_reserved: secmon@40000000 {
+			reg = <0x0 0x40000000 0x0 0x80000>;
+			no-map;
+		};
+	};    

I'm not a fan of above. If anything changes in future in BL31, U-Boot
would
need to reconfigure it anyway. Can we just skip it?    

I am not a fan neither, but last time I checked this is needed to boot.
Indeed TF-A inserts this node, with the right values, into U-Boot's DT.
And that's nicely preserved if you use that DT ($fdtcontroladdr) for
the kernel as well.
But if someone *loads* a DTB into U-Boot (to $fdt_addr_r), then
U-Boot fails to propagate the /reserved-memory node into that copy.
There does not seem to be a global notion of reserved memory in U-Boot.
Some commands (like tftp) explicitly parse the control DT to find and
respect reserved memory regions. bootm does that also, but only to
avoid placing the ramdisk or DTB into reserved memory. The information
ends up in images->lmb, but is not used to generate or amend nodes in
the target DT.
So the bits and pieces are there, but it will require some code to be
added to the generic U-Boot code.

So what do you think? Leaving this out will prevent loading DTBs into
U-Boot, at the moment, which sounds bad. I suggest we keep it in, for
now, it should not really hurt. U-Boot will hopefully start to do the
right thing soon, then we can either phase it out here (maybe when we
actually change something in TF-A), or let U-Boot fix it.    

TBH, if "soon" is really soon, I would rather wait with H616 DT until U-Boot 
supports carrying over reserved memory nodes.  

But this also carries compatibility issues. U-Boot support the H616 for
more than a year now, and the earliest possible U-Boot release having that
propagation code would be the one released in October. And then people
would still need to update first, so that's quite some months out.
And I was actually hoping to get at least the H616 DT patches off my
plate, and get them into the tree to have a stable and agreed upon base
(before this series turns into a teenager ;-)
Then we could for instance update the U-Boot H616 support.  

There is no compatibility issue here if people are using $fdtcontroladdr.

quoted

quoted

Whatever we do now, it will have 
compatibility issues. If we introduce reserved memory node now, we can't 
easily drop it later. Bootloaders are not very often updated, but kernels and 
DTB files are, at least in my experience. So when we decide to drop the node?  

I think of the three possibilities:
- Drop the node now, and ask people to not load DTBs explicitly  

This is my preferred solution. My position has always been that the devicetree
is provided by platform firmware, not the OS. The only reason for even
submitting the devicetree to Linux is because that is the location of the
bindings and validation tooling.

Well, you are barking at the wrong tree here ;-)
I am 100% behind the $fdtcontroladdr and "firmware ships DT" idea.
However this relies on one thing: that there will never be an
incompatible change to the DT. So at any point in time there must be
exactly one best DT for that board, and that DT must be able to boot
every kernel: older ones, current ones, FreeBSD ones, you name it.
Because otherwise you cannot update your DT, or you lose the ability to
boot a stable distro, or the stable fallback kernel that your distro
installed, for instance.
And this is not theoretical: Debian 11 ships with v5.10, which does not
boot with a DT from >= v5.13 (r_intc binding change for most AW SoCs).

And yes, this means we have to live with decisions we once made, and
have to make compromises, so cannot get the DT "exactly right by the
book", since we need to maintain compatibility. I strongly believe
there are solutions that allow this, even if we spot mistakes later or
need to amend something to make a new feature work. At the cost of
being potentially somewhat "hacky".

Some years ago I have been explicitly told that mainline sunxi Linux
does not have the resources to pull this off, and we don't guarantee
forward compatibility, which in my view renders this $fdtcontroladdr
approach moot. And the r_intc binding change, also the upcoming A23
clock change tell me that this is still the position among the
maintainers?

Or has this position changed for new SoCs? So do we promise to never
break compatibility for D1 and H616, and other new SoCs? Or even for
older SoCs, from now on?

I have been using this approach for D1, and so far there have been no unsolvable
problems. Yes, most image builders assume you want to load a DTB from disk, but
teaching them not to do that is fairly simple. And yes, it means we have to do
better about keeping the U-Boot DTSs in sync, but I think we can manage that.

Yes, I am very happy to update them much more regularly, and even have
some prototype tool to update the DTB directly in the FIT image on SPI
flash/eMMC boot/SD card/etc. Or I guess we rather explore the EFI
capsule update path more.
However this is all rather pointless (and actually counterproductive) if
that new DT does not boot all kernels.

quoted

- Drop the node when U-Boot learned to propagate the reservation
- Keep the node
the last one is the least painful: having this node in does not really
hurt, so we can be very relaxed with this removal decision:  

Supporting explicitly-loaded DTBs is the most painful option going forward,
because that means U-Boot has to know about and propagate _every_ runtime change
made by any firmware component (not just changes made by it) to the control FDT.

Yes, you have some point there.

For example, consider TF-A patching in information about idle states, or SID
contents in secure mode, or marking nodes as "reserved" because it delegates
those devices to a secure enclave. This problem is solved if we say "we support
$fdtcontroladdr, and we support overlays; but you are on your own if you load a
DTB from disk."

Distros will continue loading DTBs from disk as long as it sorta-kinda-mostly
works, and then years later users will complain that their phone uses 4 watts at
idle, because their explicitly-loaded DTB contained idle states that their
firmware did not support (this is a true story).

"Don't load DTBs" is a much easier story to tell if doing so is obviously broken
out of the box from day 1.

I mostly agree, from a developer's point of view. My suggestion was
just trying to embrace the (current) reality, and giving the user the
ability to load a new DTB. But yes, they should not do this.

And I actually believe distros don't really like this approach either,
it's just how mainline Linux worked for most platforms: you better run
with the latest DTB, and the one matching the kernel (whatever that
means). So I think they will be quite happy to use U-Boot's DTB, though
this needs to be the universal one.

So I think the whole discussion boils down to the question of how we
are going to deal with upcoming DT fixes? Do we allow them only in a
compatible way?
And this could be a simple thing, like adding a previously unknown
regulator to a device: older kernels might not support that regulator,
so the device now fails probing. This is a prominent problem for
initial (minimal) DTs, where we only get PMIC support later. Sure, we
could demand having PMIC support in from day one, but there might be
other things we miss (like a clock gated by the RTC).

Cheers,
Andre


  

Regards,
Samuel

quoted

- If U-Boot does not add the reserved node, we are covered.
- If U-Boot adds the node, it will do so in a way where it deals with
existing reservations. So either it doesn't actually change anything, or
it extends the reservation.
- Should the TF-A location actually move (and we have no plans or needs to
do that), people would only get this by updating the firmware, at which
point the U-Boot part would surely be in place already. We don't really
support updating just BL31 in an existing binary firmware image, so you
would get an updated U-Boot as well.

I think the worst case scenario is that users end up with an unneeded 512K
reservation. If they care, a firmware update should solve this problem.

As for the time to remove that node: we could do that at the time when
(or rather: if) we actually change the TF-A reservation. At the moment
there are no plans to do this, and the size reservation is more than
generous (the current debug build is actually 77 KB or so only). If there
is no change, and the node stays in the .dtsi, it doesn't really hurt, see
above.
  

quoted

After 10 years? Alternatively, reserved memory node can be just dropped and 
anyone loading DTB file from outside would need to make sure it's patched. But 
that's unexpected from user perspective, although patching DT files is done by 
some distros.  

Yeah, let's not go there. As you know, I already dislike the idea of
explicitly loading DTBs at all, but I understand this is what people, and
distributions, do, so I'd rather have them covered. Hence the node to
work with existing firmware.

Does that make sense?

Cheers,
Andre
  

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