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

From: Stefan Wahren
Date: Fri Sep 13 2019 - 04:51:06 EST

Am 13.09.19 um 10:09 schrieb Matthias Brugger:
> On 12/09/2019 21:32, Stefan Wahren wrote:
>> Am 12.09.19 um 19:18 schrieb Matthias Brugger:
>>> On 10/09/2019 11:27, Matthias Brugger wrote:
>>>> On 09/09/2019 21:33, Stefan Wahren wrote:
>>>>> Hi Nicolas,
>>>>> Am 09.09.19 um 11:58 schrieb Nicolas Saenz Julienne:
>>>>>> Hi all,
>>>>>> this series attempts to address some issues we found while bringing up
>>>>>> the new Raspberry Pi 4 in arm64 and it's intended to serve as a follow
>>>>>> up of these discussions:
>>>>>> v4:
>>>>>> v3:
>>>>>> v2:
>>>>>> v1:
>>>>>> RFC:
>>>>>> The new Raspberry Pi 4 has up to 4GB of memory but most peripherals can
>>>>>> only address the first GB: their DMA address range is
>>>>>> 0xc0000000-0xfc000000 which is aliased to the first GB of physical
>>>>>> memory 0x00000000-0x3c000000. Note that only some peripherals have these
>>>>>> limitations: the PCIe, V3D, GENET, and 40-bit DMA channels have a wider
>>>>>> view of the address space by virtue of being hooked up trough a second
>>>>>> interconnect.
>>>>>> Part of this is solved on arm32 by setting up the machine specific
>>>>>> '.dma_zone_size = SZ_1G', which takes care of reserving the coherent
>>>>>> memory area at the right spot. That said no buffer bouncing (needed for
>>>>>> dma streaming) is available at the moment, but that's a story for
>>>>>> another series.
>>>>>> Unfortunately there is no such thing as 'dma_zone_size' in arm64. Only
>>>>>> ZONE_DMA32 is created which is interpreted by dma-direct and the arm64
>>>>>> arch code as if all peripherals where be able to address the first 4GB
>>>>>> of memory.
>>>>>> In the light of this, the series implements the following changes:
>>>>>> - Create both DMA zones in arm64, ZONE_DMA will contain the first 1G
>>>>>> area and ZONE_DMA32 the rest of the 32 bit addressable memory. So far
>>>>>> the RPi4 is the only arm64 device with such DMA addressing limitations
>>>>>> so this hardcoded solution was deemed preferable.
>>>>>> - Properly set ARCH_ZONE_DMA_BITS.
>>>>>> - Reserve the CMA area in a place suitable for all peripherals.
>>>>>> This series has been tested on multiple devices both by checking the
>>>>>> zones setup matches the expectations and by double-checking physical
>>>>>> addresses on pages allocated on the three relevant areas GFP_DMA,
>>>>>> - On an RPi4 with variations on the ram memory size. But also forcing
>>>>>> the situation where all three memory zones are nonempty by setting a 3G
>>>>>> ZONE_DMA32 ceiling on a 4G setup. Both with and without NUMA support.
>>>>> i like to test this series on Raspberry Pi 4 and i have some questions
>>>>> to get arm64 running:
>>>>> Do you use U-Boot? Which tree?
>>>> If you want to use U-Boot, try v2019.10-rc4, it should have everything you need
>>>> to boot your kernel.
>>> Ok, here is a thing. In the linux kernel we now use bcm2711 as SoC name, but the
>>> RPi4 devicetree provided by the FW uses mostly bcm2838.
>> Do you mean the DTB provided at runtime?
>> You mean the merged U-Boot changes, doesn't work with my Raspberry Pi
>> series?
>>> U-Boot in its default
>>> config uses the devicetree provided by the FW, mostly because this way you don't
>>> have to do anything to find out how many RAM you really have. Secondly because
>>> this will allow us, in the near future, to have one U-boot binary for both RPi3
>>> and RPi4 (and as a side effect one binary for RPi1 and RPi2).
>>> Anyway, I found at least, that the following compatibles need to be added:
>>> "brcm,bcm2838-cprman"
>>> "brcm,bcm2838-gpio"
>>> Without at least the cprman driver update, you won't see anything.
>>> "brcm,bcm2838-rng200" is also a candidate.
>>> I also suppose we will need to add "brcm,bcm2838" to
>>> arch/arm/mach-bcm/bcm2711.c, but I haven't verified this.
>> How about changing this in the downstream kernel? Which is much easier.
> I'm not sure I understand what you want to say. My goal is to use the upstream
> kernel with the device tree blob provided by the FW.

The device tree blob you are talking is defined in this repository:

So the word FW is misleading to me.

> 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?


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.

>>> Regards,
>>> Matthias
>>>> Regards,
>>>> Matthias
>>>>> Are there any config.txt tweaks necessary?
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