ARM: 8617/1: dma: fix dma_max_pfn()

Since commit 6ce0d20 ("ARM: dma: Use dma_pfn_offset for dma address translation"),
dma_to_pfn() already returns the PFN with the physical memory start offset
so we don't need to add it again.

This fixes USB mass storage lock-up problem on systems that can't do DMA
over the entire physical memory range (e.g.) Keystone 2 systems with 4GB RAM
can only do DMA over the first 2GB. [K2E-EVM].

What happens there is that without this patch SCSI layer sets a wrong
bounce buffer limit in scsi_calculate_bounce_limit() for the USB mass
storage device. dma_max_pfn() evaluates to 0x8fffff and bounce_limit
is set to 0x8fffff000 whereas maximum DMA'ble physical memory on Keystone 2
is 0x87fffffff. This results in non DMA'ble pages being given to the
USB controller and hence the lock-up.

NOTE: in the above case, USB-SCSI-device's dma_pfn_offset was showing as 0.
This should have really been 0x780000 as on K2e, LOWMEM_START is 0x80000000
and HIGHMEM_START is 0x800000000. DMA zone is 2GB so dma_max_pfn should be
0x87ffff. The incorrect dma_pfn_offset for the USB storage device is because
USB devices are not correctly inheriting the dma_pfn_offset from the
USB host controller. This will be fixed by a separate patch.

Fixes: 6ce0d20 ("ARM: dma: Use dma_pfn_offset for dma address translation")
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Santosh Shilimkar <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Linus Walleij <[email protected]>
Reported-by: Grygorii Strashko <[email protected]>
Signed-off-by: Roger Quadros <[email protected]>
Signed-off-by: Russell King <[email protected]>

Author: Roger Quadros

arch/arm/include/asm/dma-mapping.h

@@ -111,7 +111,7 @@ static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
 /* The ARM override for dma_max_pfn() */
 static inline unsigned long dma_max_pfn(struct device *dev)
 {
-	return PHYS_PFN_OFFSET + dma_to_pfn(dev, *dev->dma_mask);
+	return dma_to_pfn(dev, *dev->dma_mask);
 }
 #define dma_max_pfn(dev) dma_max_pfn(dev)