Re: [PATCH v2 0/4] memory: tegra210-emc: Support Device Tree EMC Tables

[Krzysztof Kozlowski <krzk@kernel.org>]

On 08/05/2025 13:37, Aaron Kling wrote:
> On Thu, May 8, 2025 at 2:41 AM Thierry Reding <thierry.reding@gmail.com> wrote:
>>
>> On Thu, May 08, 2025 at 01:07:37AM -0500, Aaron Kling via B4 Relay wrote:
>>> Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
>>> ---
>>> Changes in v2:
>>> - Add patch to describe the emc table bindings
>>> - Add patch to allow a fallback compatible on the tegra210 emc device to
>>>   match firmware expectations
>>> - Add a patch to include the baseline emc tables on p2180
>>> - Link to v1: https://lore.kernel.org/r/20250430-tegra210-emc-dt-v1-1-99896fa69341@gmail.com
>>>
>>> ---
>>> Aaron Kling (4):
>>>       dt-bindings: memory-controllers: Describe Tegra210 EMC Tables
>>>       dt-bindings: memory-controllers: tegra210: Allow fallback compatible
>>>       arm64: tegra: Add EMC timings to P2180
>>>       memory: tegra210-emc: Support Device Tree EMC Tables
>>>
>>>  .../nvidia,tegra21-emc-table.yaml                  |  1692 +
>>>  .../memory-controllers/nvidia,tegra210-emc.yaml    |    44 +-
>>>  arch/arm64/boot/dts/nvidia/tegra210-p2180-emc.dtsi | 49749 +++++++++++++++++++
>>>  arch/arm64/boot/dts/nvidia/tegra210-p2180.dtsi     |     1 +
>>>  drivers/memory/tegra/tegra210-emc-core.c           |   246 +-
>>>  5 files changed, 51721 insertions(+), 11 deletions(-)
>>
>> We've had discussions about this in the past, and I don't think this is
>> going to go anywhere. Device tree maintainers have repeatedly said that
>> they won't accept this kind of binding, which is, admittedly, a bit non-
>> sensical. 50,000 lines of DT for EMC tables is just crazy.
>>
>> The existing binary table bindings were created to avoid the need for
>> this. I don't know how easy this is to achieve for all bootloaders, but
>> the expectation was that these tables should be passed in their native
>> format.
> 
> Mmm, this would definitely be an issue with my long term end goal of
> supporting the SHIELD t210 devices on mainline. The bootloader on
> those devices cannot be replaced due to secure boot and that variant
> of the bootloader only supports this dt table for emc. And support
> without emc reclocking would be rather unusable as a consumer media
> device. Unless the devices could get a bootloader update switching to
> the reserved memory tables before they go eol, but I don't see that as
> likely.
> 
> So I guess the question goes to Krzysztof. I didn't have the bindings

What is the question exactly?

> or a copy of the tables in v1 of this series, mostly due to a
> misunderstanding, and was fairly asked to add them. That's this
> revision. Would you consider accepting this after any fixes? Or is
> this concept entirely dead in the water?


The binding here is far away from what is in general acceptable DTS
style, so in general this won't be easy to upstream. If we allow any
crap to be sent post factum, what is the benefit for companies to
actually took to community BEFORE they ship products? None, because that
crap will be always sent after release with explanation "we cannot
change now". Old platforms with Android bootloaders are in general
encouraged to move to something decent, like U-boot.

50 kB DTS is another point - I don't even understand why do you need it
if you claim this is coming from bootloader.


Best regards,
Krzysztof