linux-kernel - Re: [PATCH] ARM: dts: dra7: Add bus_dma

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Message-ID: <e031b768-8fb8-ce62-a644-69925757cbc6@arm.com>
Date:   Wed, 11 Mar 2020 15:47:12 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Tony Lindgren <tony@...mide.com>, Roger Quadros <rogerq@...com>
Cc:     Tero Kristo <t-kristo@...com>, hch@....de, robh+dt@...nel.org,
        nm@...com, nsekhar@...com, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: dra7: Add bus_dma_limit for L3 bus

On 11/03/2020 3:23 pm, Tony Lindgren wrote:
> * Roger Quadros <rogerq@...com> [200311 07:21]:
>>
>>
>> On 10/03/2020 17:48, Tony Lindgren wrote:
>>> * Tero Kristo <t-kristo@...com> [200310 14:46]:
>>>> On 10/03/2020 13:53, Roger Quadros wrote:
>>>>> The L3 interconnect can access only 32-bits of address.
>>>>> Add the dma-ranges property to reflect this limit.
>>>>>
>>>>> This will ensure that no device under L3 is
>>>>> given > 32-bit address for DMA.
>>>>>
>>>>> Issue was observed only with SATA on DRA7-EVM with 4GB RAM
>>>>> and CONFIG_ARM_LPAE enabled. This is because the controller
>>>>> can perform 64-bit DMA and was setting the dma_mask to 64-bit.
>>>>>
>>>>> Setting the correct bus_dma_limit fixes the issue.
>>>>
>>>> This seems kind of messy to modify almost every DT node because of this....
>>>> Are you sure this is the only way to get it done? No way to modify the sata
>>>> node only which is impacted somehow?
>>>>
>>>> Also, what if you just pass 0xffffffff to the dma-ranges property? That
>>>> would avoid modifying every node I guess.
>>>
>>> Also, I think these interconnects are not limited to 32-bit access.
>>
>> But from Table 2-1. L3_MAIN Memory Map
>>
>> Start address	0x0000_0000
>> End address	0xFFFF_FFFF
>>
>> So it is 32-bit limit, right?
> 
> Hmm so what war Robin saying earlier that DMA access seems to be
> limited to lower 2GB only though?

That's the lower 2GB *of DRAM*, which occupies the upper 2GB of the L3 
memory map ;)

Robin.