dma-mapping: replace zone_dma_bits by zone_dma_limit

The hardware DMA limit might not be power of 2. When RAM range starts
above 0, say 4GB, DMA limit of 30 bits should end at 5GB.  A single high
bit can not encode this limit.

Use a plain  address for the DMA zone limit instead.

Since the DMA zone can now potentially span beyond 4GB physical limit of
DMA32, make sure to use DMA zone for GFP_DMA32 allocations in that case.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Co-developed-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Petr Tesarik <ptesarik@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

3 files changed, 20 insertions, 17 deletions

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9b5ab6818f7f..c45e2152ca9e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -115,35 +115,35 @@ static void __init arch_reserve_crashkernel(void)
 }
 
 /*
- * Return the maximum physical address for a zone accessible by the given bits
- * limit. If DRAM starts above 32-bit, expand the zone to the maximum
+ * Return the maximum physical address for a zone given its limit.
+ * If DRAM starts above 32-bit, expand the zone to the maximum
  * available memory, otherwise cap it at 32-bit.
  */
-static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
+static phys_addr_t __init max_zone_phys(phys_addr_t zone_limit)
 {
-	phys_addr_t zone_mask = DMA_BIT_MASK(zone_bits);
 	phys_addr_t phys_start = memblock_start_of_DRAM();
 
 	if (phys_start > U32_MAX)
-		zone_mask = PHYS_ADDR_MAX;
-	else if (phys_start > zone_mask)
-		zone_mask = U32_MAX;
+		zone_limit = PHYS_ADDR_MAX;
+	else if (phys_start > zone_limit)
+		zone_limit = U32_MAX;
 
-	return min(zone_mask, memblock_end_of_DRAM() - 1) + 1;
+	return min(zone_limit, memblock_end_of_DRAM() - 1) + 1;
 }
 
 static void __init zone_sizes_init(void)
 {
 	unsigned long max_zone_pfns[MAX_NR_ZONES]  = {0};
-	unsigned int __maybe_unused acpi_zone_dma_bits;
-	unsigned int __maybe_unused dt_zone_dma_bits;
-	phys_addr_t __maybe_unused dma32_phys_limit = max_zone_phys(32);
+	phys_addr_t __maybe_unused acpi_zone_dma_limit;
+	phys_addr_t __maybe_unused dt_zone_dma_limit;
+	phys_addr_t __maybe_unused dma32_phys_limit =
+		max_zone_phys(DMA_BIT_MASK(32));
 
 #ifdef CONFIG_ZONE_DMA
-	acpi_zone_dma_bits = fls64(acpi_iort_dma_get_max_cpu_address());
-	dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL));
-	zone_dma_bits = min3(32U, dt_zone_dma_bits, acpi_zone_dma_bits);
-	arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
+	acpi_zone_dma_limit = acpi_iort_dma_get_max_cpu_address();
+	dt_zone_dma_limit = of_dma_get_max_cpu_address(NULL);
+	zone_dma_limit = min(dt_zone_dma_limit, acpi_zone_dma_limit);
+	arm64_dma_phys_limit = max_zone_phys(zone_dma_limit);
 	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
 #endif
 #ifdef CONFIG_ZONE_DMA32
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index da21cb018984..7e217aa4a274 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -216,7 +216,7 @@ static int __init mark_nonram_nosave(void)
  * everything else. GFP_DMA32 page allocations automatically fall back to
  * ZONE_DMA.
  *
- * By using 31-bit unconditionally, we can exploit zone_dma_bits to inform the
+ * By using 31-bit unconditionally, we can exploit zone_dma_limit to inform the
  * generic DMA mapping code.  32-bit only devices (if not handled by an IOMMU
  * anyway) will take a first dip into ZONE_NORMAL and get otherwise served by
  * ZONE_DMA.
@@ -230,6 +230,7 @@ void __init paging_init(void)
 {
 	unsigned long long total_ram = memblock_phys_mem_size();
 	phys_addr_t top_of_ram = memblock_end_of_DRAM();
+	int zone_dma_bits;
 
 #ifdef CONFIG_HIGHMEM
 	unsigned long v = __fix_to_virt(FIX_KMAP_END);
@@ -256,6 +257,8 @@ void __init paging_init(void)
 	else
 		zone_dma_bits = 31;
 
+	zone_dma_limit = DMA_BIT_MASK(zone_dma_bits);
+
 #ifdef CONFIG_ZONE_DMA
 	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
 				      1UL << (zone_dma_bits - PAGE_SHIFT));
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index e3d258f9e726..688abc65c79e 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -97,7 +97,7 @@ void __init paging_init(void)
 
 	vmem_map_init();
 	sparse_init();
-	zone_dma_bits = 31;
+	zone_dma_limit = DMA_BIT_MASK(31);
 	memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
 	max_zone_pfns[ZONE_DMA] = virt_to_pfn(MAX_DMA_ADDRESS);
 	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;