Patch "ARM: 8617/1: dma: fix dma_max_pfn()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm-8617-1-dma-fix-dma_max_pfn.patch

and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Roger Quadros <[email protected]>
Date: Thu, 29 Sep 2016 08:32:55 +0100
Subject: ARM: 8617/1: dma: fix dma_max_pfn()

From: Roger Quadros <[email protected]>

commit d248220f0465b818887baa9829e691fe662b2c5e upstream.

Since commit 6ce0d2001692 ("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.

---
 arch/arm/include/asm/dma-mapping.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -119,7 +119,7 @@ static inline dma_addr_t virt_to_dma(str
 /* 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)
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arm-8617-1-dma-fix-dma_max_pfn.patch