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

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Date:   Wed, 11 Mar 2020 09:20:05 +0200
From:   Roger Quadros <rogerq@...com>
To:     Tony Lindgren <tony@...mide.com>, Tero Kristo <t-kristo@...com>
CC:     <hch@....de>, <robin.murphy@....com>, <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 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?

> So yeah I too would prefer a top level dma-ranges property assuming
> that works.
> 
> I guess there dma-ranges should not be 0xffffffff though if
> limited to 2GB :)
> 
> Regards,
> 
> Tony
> 

-- 
cheers,
-roger
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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