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Subject: Re: [PATCH v5 0/4] Raspberry Pi 4 DMA addressing support
To:     Matthias Brugger <matthias.bgg@gmail.com>,
        Matthias Brugger <mbrugger@suse.com>,
        Stefan Wahren <wahrenst@gmx.net>, catalin.marinas@arm.com,
        marc.zyngier@arm.com, robh+dt@kernel.org, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, hch@lst.de,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc:     f.fainelli@gmail.com, robin.murphy@arm.com,
        linux-kernel@vger.kernel.org, linux-rpi-kernel@lists.infradead.org,
        phill@raspberrypi.org, will@kernel.org, m.szyprowski@samsung.com
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From:   Stefan Wahren <wahrenst@gmx.net>
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Date:   Thu, 12 Sep 2019 21:32:16 +0200
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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 foll=
ow
>>>> 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 t=
hese
>>>> limitations: the PCIe, V3D, GENET, and 40-bit DMA channels have a wi=
der
>>>> view of the address space by virtue of being hooked up trough a seco=
nd
>>>> interconnect.
>>>>
>>>> Part of this is solved on arm32 by setting up the machine specific
>>>> '.dma_zone_size =3D SZ_1G', which takes care of reserving the cohere=
nt
>>>> 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. On=
ly
>>>> ZONE_DMA32 is created which is interpreted by dma-direct and the arm=
64
>>>> arch code as if all peripherals where be able to address the first 4=
GB
>>>> 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 limitat=
ions
>>>>   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 forcin=
g
>>>>   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 suppo=
rt.
>>>>
>>> i like to test this series on Raspberry Pi 4 and i have some question=
s
>>> 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 b=
oth 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 add=
ed:
>
> "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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>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
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