Re: [PATCH v2] ARM: dts: tegra: Add support for 256 MB Colibri-T20 (plus such board on Iris)

On Tue, 2018-05-08 at 14:35 +0200, Krzysztof Kozlowski wrote:

On Fri, May 4, 2018 at 12:14 PM, Marcel Ziswiler
[off-list ref] wrote:

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Hi Krzysztof

On Fri, 2018-05-04 at 12:03 +0200, Krzysztof Kozlowski wrote:

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On Fri, May 4, 2018 at 11:19 AM, Stefan Agner [off-list ref]
wrote:

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On 03.05.2018 17:08, Krzysztof Kozlowski wrote:

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Colibri-T20 can come in 256 MB RAM (with 512 MB NAND) or 512
MB
RAM
(with 1024 MB NAND) flavors.  Add support for the 256 MB
version
on Iris
evaluation board.

To we really need to specify memory size these days? I think
all
common
boot loaders fill the memory node anyway.

arch/arm/boot/dts/imx6qdl-apalis.dtsi:
        /* Will be filled by the bootloader */
        memory@10000000 {
                reg = <0x10000000 0>;
        };


I think we should just rename tegra20-colibri-512.dtsi =>
tegra20-colibri.dtsi and tegra20-iris-512.dts => tegra20-
iris.dts
to
avoid confusion and add such an empty node.

Having memory node is requirement of DeviceTree specification (at
least one cpu and memory node). Of course if bootloader fills it,
then
we could assume that specification is satisfied... but what if
some
bootloader skips it? This creates quite specific dependency
between
kernel's DTS and bootloader.

Yes, no system boots without any boot loader e.g. initialising the
memory and what not. So there are obviously quite specific
dependencies.

Sorry for late reply, I missed your emails because unfortunately
Google marks messages coming for Toradex as spam ("This message has a
from address in toradex.com but has failed toradex.com's required
tests for authentication.").

Argh, I guess that happens if you have stubborn IT departments which
still believe in M$. Sending via private email now.

Therefore I did not include your comments
and sent v3.

Yeah, I noticed that. It's forgiven, don't worry (;-p).

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One safe solution would be to specify 256 MB memory node for both
boards and assume that bootloader will bump it to 512 MB for
specific
module.

Like I mentioned this actually used to be how it was done however
lately it has been agreed that any boot loader anyway needs to do
the
device tree dance (e.g. even just loading and passing it).

Then the safest way is to provide /memory node with 256 MB. If some
bootloader omits it (e.g. because it is too old or by any mistake)
the
FDT will be still usable with reduced memory in case of 512 board.

Makes sense.

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Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

---

Changes since v1:
1. Fix memory size in tegra20-colibri-256.dtsi (was working
fine
because
   my bootloader uses mem= argument).

What boot loader are you using? You even can omit mem= if your
boot
loader fills the memory node properly.

I use the one provided by vendor - Toradex. By default it passes
both
mem= and few other mem-like arguments (for FB and video
processor) to
command line. I believe it does not adjust the DTB itself because
Toradex prepared this bootloader for... 3.1 kernel without DTB. 7
years old kernel. :)

Remember our regular BSP is still based on NVIDIA's downstream
Linux
for Tegra aka L4T R16.5 based on Linux kernel 3.1.10 which does not
even use any device tree yet.

Yes, I noticed. I am trying to bring it fully on new kernels but no
huge successes so far... I'm stuck on NAND trying Lucas Stach's old
patchset.

Yeah, for a while I kept his patch set alive as well. I believe 4.4 was
still working fine passing all MTD tests. However, lately there were so
many changes it all fell apart. About a month ago I spend a couple
nights trying to get it running again but something is still not quite
right. Yet have to sync with Stefan in my team who is much more
knowledgeable about latest NAND development.

Best regards,
Krzysztof

Cheers

Marcel