Re: [PATCH 2/3] ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE

[santosh . shilimkar]

On 9/11/20 4:15 AM, Russell King - ARM Linux admin wrote:
> On Thu, Sep 10, 2020 at 07:40:37AM +0200, Christoph Hellwig wrote:
> > The DMA offset notifier can only be used if PHYS_OFFSET is at least
> > KEYSTONE_HIGH_PHYS_START, which can't be represented by a 32-bit
> > phys_addr_t.  Currently the code compiles fine despite that, a pending
> > change to the DMA offset handling would create a compiler warning for
> > this case.  Add an ifdef to not compile the code except for LPAE
> > configs.
>
> However, to have use of the high physical offset, LPAE needs to be
> enabled, which ensures that phys_addr_t is 64-bit.
>
> I believe that DMA is non-coherent on this platform unless the high
> physical address is used. Or something like that.
Exactly. Higher address ranges needs to be used for DMA coherency.

Regards,
Santosh