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SubjectRe: [PATCH] arm64: fix CONFIG_ZONE_DMA on systems with no 32-bit addressable DRAM
On Wed, Jun 25, 2014 at 01:26:02AM +0100, David Rientjes wrote:
> On Mon, 23 Jun 2014, Mark Salter wrote:
>
> > Commit 2d5a5612bc (arm64: Limit the CMA buffer to 32-bit if ZONE_DMA)
> > forces the CMA buffer to be 32-bit addressable if CONFIG_ZONE_DMA is
> > defined. This breaks CMA on platforms with no 32-bit addressable DRAM.
> > This patch checks to make sure there is 32-bit addressable DRAM before
> > setting the 32-bit limit. If there is none, no limit is placed on the
> > CMA buffer. This allows a single kernel (with CONFIG_ZONE_DMA defined)
> > to support platforms requiring the 32-bit limit and platforms with no
> > 32-bit limit.
> >
> > Signed-off-by: Mark Salter <msalter@redhat.com>
> > ---
> > arch/arm64/mm/init.c | 11 ++++++++++-
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index c5415e2..2925576 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -149,8 +149,17 @@ void __init arm64_memblock_init(void)
> > early_init_fdt_scan_reserved_mem();
> >
> > /* 4GB maximum for 32-bit only capable devices */
> > - if (IS_ENABLED(CONFIG_ZONE_DMA))
> > + if (IS_ENABLED(CONFIG_ZONE_DMA)) {
> > dma_phys_limit = dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1;
> > + /*
> > + * If platform doesn't have DRAM within the dma_phys_limit,
> > + * remove the limit altogether. This allows one kernel (with
> > + * CONFIG_ZONE_DMA defined) to support platforms with 32-bit
> > + * only devices and platforms with no 32-bit DRAM.
> > + */
> > + if (dma_phys_limit <= memblock_start_of_DRAM())
> > + dma_phys_limit = 0;
> > + }
> > dma_contiguous_reserve(dma_phys_limit);
> >
> > memblock_allow_resize();
>
> It is a shame that we have very similar logic, all dependent on
> memblock_start_of_DRAM(), in both zone_sizes_init() and
> arm64_memblock_init() and the latter having to be called before the
> former. I assume there's no way to make this cleaner in the bootstrap
> code so the dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1 limit can be handled
> properly in a single location?

Probably and I suggested something along the lines of only calculating
it once in reply to the "[PATCH] arm64: make CONFIG_ZONE_DMA user
settable" message. I'll follow up on the other thread (Mark considers
there's a penalty issue with all memory in the DMA zone).

--
Catalin


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