From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
Subject: Re: [PATCH v2] iommu/io-pgtable-arm: Don't use dma_to_phys()
Date: Fri, 18 Sep 2015 13:29:37 +0100
Message-ID: <20150918122937.GE21084@n2100.arm.linux.org.uk>
References: <59f4ebbf06e75a6176a366495211afd16d0048a3.1442507940.git.robin.murphy@arm.com>
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To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
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On Fri, Sep 18, 2015 at 12:04:26PM +0100, Robin Murphy wrote:
> Specifically, the problem case for that is when phys_addr_t is 64-bit but
> dma_addr_t is 32-bit. The cast in __arm_lpae_dma_addr is necessary to avoid
> a truncation warning when we make the DMA API calls, but we actually need
> the opposite in the comparison here - comparing the different types directly
> allows integer promotion to kick in appropriately so we don't lose the top
> half of the larger address. Otherwise, you'd never spot the difference
> between, say, your original page at 0x88c0000000 and a bounce-buffered copy
> that happened to end up mapped to 0xc0000000.

Hmm.  Thinking about this, I think we ought to add to arch/arm/mm/Kconfig:

 config ARCH_PHYS_ADDR_T_64BIT
 	def_bool ARM_LPAE
 
 config ARCH_DMA_ADDR_T_64BIT
 	bool
+	select ARCH_PHYS_ADDR_T_64BIT

I seem to remember that you're quite right that dma_addr_t <= phys_addr_t
but dma_addr_t must never be bigger than phys_addr_t.

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