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Subject: Re: [PATCH] ARM: dts: bcm2711: fix soc's node dma-ranges
To:     Florian Fainelli <f.fainelli@gmail.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Eric Anholt <eric@anholt.net>, Stefan Wahren <wahrenst@gmx.net>
Cc:     mbrugger@suse.com, devicetree@vger.kernel.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20191204125633.27696-1-nsaenzjulienne@suse.de>
 <711470d3-e683-69d4-8f4e-791a76faab29@gmail.com>
 <e72de603-2ad9-5a3b-109e-8ee14bf3293c@raspberrypi.org>
 <b778e086-378d-9271-6370-7fd4e60ae250@gmail.com>
From:   Phil Elwell <phil@raspberrypi.org>
Message-ID: <c085e99f-c1b3-1729-0170-fa17a1aea995@raspberrypi.org>
Date:   Mon, 9 Dec 2019 09:16:35 +0000
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On 06/12/2019 18:13, Florian Fainelli wrote:
> On 12/6/19 2:16 AM, Phil Elwell wrote:
>> Hi Nicolas,
>>
>> On 06/12/2019 00:08, Florian Fainelli wrote:
>>> On 12/4/19 4:56 AM, Nicolas Saenz Julienne wrote:
>>>> Raspberry Pi's firmware has a feature to select how much memory to
>>>> reserve for its GPU called 'gpu_mem'. The possible values go from 16MB
>>>> to 944MB, with a default of 64MB. This memory resides in the topmost
>>>> part of the lower 1GB memory area and grows bigger expanding towards the
>>>> begging of memory.
>>>>
>>>> It turns out that with low 'gpu_mem' values (16MB and 32MB) the size of
>>>> the memory available to the system in the lower 1GB area can outgrow the
>>>> interconnect's dma-range as its size was selected based on the maximum
>>>> system memory available given the default gpu_mem configuration. This
>>>> makes that memory slice unavailable for DMA. And may cause nasty kernel
>>>> warnings if CMA happens to include it.
>>>>
>>>> Change soc's dma-ranges to really reflect it's HW limitation, which is
>>>> being able to only DMA to the lower 1GB area.
>>>>
>>>> Fixes: 7dbe8c62ceeb ("ARM: dts: Add minimal Raspberry Pi 4 support")
>>>> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
>>>> ---
>>>>
>>>> NOTE: I'd appreciate if someone from the RPi foundation commented on
>>>> this as it's something that I'll propose to be backported to their tree.
>>
>> The 0x3c000000 size was a mistake that arose from c0000000 + 3c000000 =
>> fc000000, but that is mixing apples and oranges (actually DMA addresses
>> and host physical addresses). Please correct it as you are proposing.
> 
> Do you want to add an Acked-by or Reviewed-by tag to make this statement
> official?

Here you go:

Reviewed-by: Phil Elwell <phil@raspberrypi.org>