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

From: Matthias Brugger <[email-masked]>
Date: Fri, 13 Sep 2019 09:15:44 +0200

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: 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?
> 

Yes.

> You mean the merged U-Boot changes, doesn't work with my Raspberry Pi
> series?
> 

Unfortunately that is exactly the state right now.

>>  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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