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

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Date:   Wed, 11 Mar 2020 08:49:09 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Roger Quadros <rogerq@...com>, 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

* Robin Murphy <robin.murphy@....com> [200311 15:48]:
> 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 ;)

OK thanks for clarifying it.

Regards,

Tony