linux-kernel - Re: [PATCH v5 0/4] Raspberry Pi 4 DMA addressing support

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Message-ID: <c7e6ab89-aaae-debc-5f63-2e091efcf76f@gmx.net>
Date:   Mon, 16 Sep 2019 21:19:17 +0200
From:   Stefan Wahren <wahrenst@....net>
To:     Matthias Brugger <matthias.bgg@...il.com>,
        Matthias Brugger <mbrugger@...e.com>, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     f.fainelli@...il.com, linux-rpi-kernel@...ts.infradead.org,
        phil@...pberrypi.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/4] Raspberry Pi 4 DMA addressing support

Hi Matthias,

[drop uninvolved receiver]

Am 13.09.19 um 12:39 schrieb Matthias Brugger:
>
>>>>>  If you talk about the
>>>>> downstream kernel, I suppose you mean we should change this in the FW DT blob
>>>>> and in the downstream kernel. That would work for me.
>>>>>
>>>>> Did I understand you correctly?
>>>> Yes
>>>>
>>>> So i suggest to add the upstream compatibles into the repo mentioned above.
>>>>
>>>> Sorry, but in case you decided as a U-Boot developer to be compatible
>>>> with a unreviewed DT, we also need to make U-Boot compatible with
>>>> upstream and downstream DT blobs.
>>>>
>>> Well RPi3 is working with the DT blob provided by the FW, as I mentioned earlier
>>> if we can use this DTB we can work towards one binary that can boot both RPi3
>>> and RPi4. On the other hand we can rely on the FW to detect the amount of memory
>>> our RPi4 has.
>>>
>>> That said, I agree that we should make sure that U-Boot can boot with both DTBs,
>>> the upstream one and the downstream. Now the question is how to get to this. I'm
>>> a bit puzzled that by talking about "unreviewed DT" you insinuate that bcm2711
>>> compatible is already reviewed and can't be changed. From what I can see none of
>>> these compatibles got merged for now, so we are still at time to change them.
>> Stephen Boyd was okay with clk changes except of a small nit. So i fixed
>> this is as he suggested in a separate series. Unfortunately this hasn't
>> be applied yet [1].
>>
>> The i2c, pinctrl and the sdhci changes has been applied yet.
>>
>> In my opinion it isn't the job of the mainline kernel to adapt to a
>> vendor device tree. It's the vendor device tree which needs to be fixed.
>>
> I agree with that. But if we can make this easier by choosing a compatible which
> fits downstream without violating upstream and it makes sense with the naming
> scheme of the RPi, I think that's a good argument.

i spend a lot of my spare time to prepare these patch series in order to
get a clean solution.

Either mixing bcm2711/bcm2838 or changing everything to bcm2838 in the
upstream tree has the following drawbacks:

- additional review time and delay of the Raspberry Pi 4 support
- harder to understand for developer/reviewer without RPi knowledge

Btw currently u-boot only uses bcm2711, so it would be nice to keep that.

So my suggestion is to add bcm2711 compatibles in the downstream tree.

Best regards
Stefan

>
>> Sorry, but this is my holiday. I will back after the weekend.
>>
> Sure, enjoy. I'll be on travel for the next two weeks but will try to keep up
> with emails.
>
> Regards,
> Matthias
>
>> Best regards
>> Stefan
>>
>> [1] - https://www.spinics.net/lists/linux-clk/msg40534.html
>>
>>> Apart from the point Florian made, to stay consistent with the RPi SoC naming,
>>> it will save us work, both in the kernel and in U-Boot, as we would need to add
>>> both compatibles to the code-base.
>>>
>>> Regards,
>>> Matthias
>>>
>>>>>>> Regards,
>>>>>>> Matthias
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Matthias
>>>>>>>>
>>>>>>>>> Are there any config.txt tweaks necessary?
>>>>>>>>>
>>>>>>>>>
>>>>>>>> _______________________________________________
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>>>>>>>> linux-arm-kernel@...ts.infradead.org
>>>>>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>>>>>>>
>>>>>>> _______________________________________________
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