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Date:   Wed, 16 Nov 2022 12:44:50 +0000
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Subject: Re: [PATCH] arm64: dts: fsd: Change the reg properties from 64-bit to
 32-bit
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From:   Robin Murphy <robin.murphy@arm.com>
To:     Arnd Bergmann <arnd@arndb.de>,
        Vivek Yadav <vivek.2311@samsung.com>, rcsekar@samsung.com,
        krzysztof.kozlowski+dt@linaro.org,
        Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, pankaj.dubey@samsung.com,
        ravi.patel@samsung.com, Alim Akhtar <alim.akhtar@samsung.com>,
        linux-fsd@tesla.com, Rob Herring <robh+dt@kernel.org>
Cc:     linux-can@vger.kernel.org, Netdev <netdev@vger.kernel.org>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, devicetree@vger.kernel.org,
        aswani.reddy@samsung.com, sriranjani.p@samsung.com,
        ajaykumar.rs@samsung.com
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On 2022-11-16 12:38, Robin Murphy wrote:
> On 2022-11-16 11:16, Arnd Bergmann wrote:
>> On Wed, Nov 16, 2022, at 10:12, Vivek Yadav wrote:
>>> Change the reg properties from 64-bit to 32-bit for all IPs, as none of
>>> the nodes are above 32-bit range in the fsd SoC.
>>>
>>> Since dma-ranges length does not fit into 32-bit size, keep it 64-bit
>>> and move it to specific node where it is used instead of SoC section.
>>
>> I don't think that works, the dma-ranges property is part of the
>> bus, not a particular device:
>>
>>           mdma0: dma-controller@10100000 {
>>               compatible = "arm,pl330", "arm,primecell";
>> -            reg = <0x0 0x10100000 0x0 0x1000>;
>> +            reg = <0x10100000 0x1000>;
>>               interrupts = <GIC_SPI 424 IRQ_TYPE_LEVEL_HIGH>;
>>               #dma-cells = <1>;
>>               clocks = <&clock_imem IMEM_DMA0_IPCLKPORT_ACLK>;
>>               clock-names = "apb_pclk";
>>               iommus = <&smmu_imem 0x800 0x0>;
>> +            #address-cells = <2>;
>> +            #size-cells = <2>;
>> +            dma-ranges = <0x0 0x0 0x0 0x10 0x0>;
>>           };
>>
>> Since the dma-controller has no children, I don't see how this has
>> any effect. Also, translating a 36-bit address into a 32-bit
>> address just means it gets truncated anyway, so there is no
>> point in making it appear to have a larger address range.
> 
> Yes, this is definitely bogus on both counts.

Oh, and also that PL330 can only do 32-bit DMA anyway :)

Thanks,
Robin.