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

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Message-ID: <20200310154829.GS37466@atomide.com>
Date:   Tue, 10 Mar 2020 08:48:29 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Tero Kristo <t-kristo@...com>
Cc:     Roger Quadros <rogerq@...com>, 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

* 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.
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