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

[Stefan Wahren]

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: https://lkml.org/lkml/2019/9/6/352
>>>> v3: https://lkml.org/lkml/2019/9/2/589
>>>> v2: https://lkml.org/lkml/2019/8/20/767
>>>> v1: https://lkml.org/lkml/2019/7/31/922
>>>> RFC: https://lkml.org/lkml/2019/7/17/476
>>>>
>>>> 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,
>>>> GFP_DMA32, GFP_KERNEL:
>>>>
>>>> - 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.
>
> Regards,
> Matthias
>
>> Regards,
>> Matthias
>>
>>> Are there any config.txt tweaks necessary?
>>>
>>>
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