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    Subject[PATCH 1/1] ARM: dma: fix dma_max_pfn()
    Date
    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.

    Fixes: 6ce0d2001692 ("ARM: dma: Use dma_pfn_offset for dma address translation")
    Cc: stable@vger.kernel.org
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Russell King <linux@arm.linux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Olof Johansson <olof@lixom.net>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Reported-by: Grygorii Strashko <grygorii.strashko@ti.com>
    Signed-off-by: Roger Quadros <rogerq@ti.com>
    ---
    arch/arm/include/asm/dma-mapping.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
    index d009f79..bf02dbd 100644
    --- a/arch/arm/include/asm/dma-mapping.h
    +++ b/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)

    --
    2.7.4
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