Re: [PATCH 3/7] drivers: dma-coherent: Account dma_pfn_offset when used with device tree

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 21/02/17 12:37, Robin Murphy wrote:
> On 15/02/17 09:59, Vladimir Murzin wrote:
>> dma_declare_coherent_memory() and friends are designed to account
>> difference in CPU and device addresses. However, when it is used with
>> reserved memory regions there is assumption that CPU and device have
>> the same view on address space. This assumption gets invalid when
>> reserved memory for coherent DMA allocations is referenced by device
>> with non-empty "dma-range" property.
>>
>> Simply feeding device address as rmem->base + dev->dma_pfn_offset
>> would not work due to reserved memory region can be shared, so this
>> patch turns device address to be expressed with help of CPU address
>> and device's dma_pfn_offset.
>>
>> For the case where device tree is not used and device sees memory
>> different to CPU we explicitly set device's dma_pfn_offset to
>> accomplish such difference. The latter might look controversial, but
>> it seems only a few drivers set device address different to CPU's:
>> - drivers/usb/host/ohci-sm501.c
>> - arch/sh/drivers/pci/fixups-dreamcast.c
>> so they can be screwed only if dma_pfn_offset there is set and not in
>> sync with device address range - we try to catch such cases with
>> WARN_ON.
>>
>> Cc: Michal Nazarewicz <mina86@mina86.com>
>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
>> Cc: Alan Stern <stern@rowland.harvard.edu>
>> Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
>> Cc: Rich Felker <dalias@libc.org>
>> Cc: Roger Quadros <rogerq@ti.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
>> Tested-by: Andras Szemzo <sza@esh.hu>
>> Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> ---
>>  drivers/base/dma-coherent.c | 17 +++++++++++++++--
>>  1 file changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
>> index 640a7e6..c59708c 100644
>> --- a/drivers/base/dma-coherent.c
>> +++ b/drivers/base/dma-coherent.c
>> @@ -18,6 +18,12 @@ struct dma_coherent_mem {
>>  	spinlock_t	spinlock;
>>  };
>>  
>> +static inline dma_addr_t dma_get_device_base(struct device *dev,
>> +					     struct dma_coherent_mem * mem)
>> +{
>> +	return (mem->pfn_base - dev->dma_pfn_offset) << PAGE_SHIFT;
>> +}
>> +
>>  static bool dma_init_coherent_memory(
>>  	phys_addr_t phys_addr, dma_addr_t device_addr, size_t size, int flags,
>>  	struct dma_coherent_mem **mem)
>> @@ -83,9 +89,16 @@ static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
>>  static int dma_assign_coherent_memory(struct device *dev,
>>  				      struct dma_coherent_mem *mem)
>>  {
>> +	unsigned long dma_pfn_offset = mem->pfn_base - PFN_DOWN(mem->device_base);
>> +
>>  	if (dev->dma_mem)
>>  		return -EBUSY;
>>  
>> +	if (dev->dma_pfn_offset)
>> +		WARN_ON(dma_pfn_offset && (dev->dma_pfn_offset != dma_pfn_offset));
>> +	else
>> +		dev->dma_pfn_offset = dma_pfn_offset;
> 
> This makes me rather uneasy - I can well imagine a device sharing the
> CPU physical address map of external system memory, but having its own
> view of its local coherent memory such that pfn_base != device_base
> still. I know for a fact we've had internal FPGA tiles set up that way,
> although whether it was entirely intentional is another matter... ;)
> 
> In that situation, setting dev->dma_pfn_offset like this would break
> streaming DMA for such devices. Could we not keep the pool-specific
> offset and the device-specific offset independent, apply whichever is
> non-zero, and scream if both are set?

Something like fixup bellow?

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 0c577ea..2060010 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -30,7 +30,15 @@ static inline struct dma_coherent_mem *dev_get_coherent_memory(struct device *de
 static inline dma_addr_t dma_get_device_base(struct device *dev,
 					     struct dma_coherent_mem * mem)
 {
-	return (mem->pfn_base - dev->dma_pfn_offset) << PAGE_SHIFT;
+	unsigned long dma_pfn_offset = mem->pfn_base - PFN_DOWN(mem->device_base);
+
+	if (dma_pfn_offset != dev->dma_pfn_offset )
+		WARN_ON(device_pfn_offset && dev->dma_pfn_offset);
+
+	if (dma_pfn_offset)
+		return mem->device_base;
+	else
+		return (mem->pfn_base - dev->dma_pfn_offset) << PAGE_SHIFT;
 }
 
 static bool dma_init_coherent_memory(
@@ -98,19 +106,12 @@ static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
 static int dma_assign_coherent_memory(struct device *dev,
 				      struct dma_coherent_mem *mem)
 {
-	unsigned long dma_pfn_offset = mem->pfn_base - PFN_DOWN(mem->device_base);
-
 	if (!dev)
 		return -ENODEV;
 
 	if (dev->dma_mem)
 		return -EBUSY;
 
-	if (dev->dma_pfn_offset)
-		WARN_ON(dma_pfn_offset && (dev->dma_pfn_offset != dma_pfn_offset));
-	else
-		dev->dma_pfn_offset = dma_pfn_offset;
-
 	dev->dma_mem = mem;
 	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */


Cheers
Vladimir

> 
> Robin.
> 
>> +
>>  	dev->dma_mem = mem;
>>  	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */
>>  
>> @@ -133,7 +146,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
>>  		return ERR_PTR(-EINVAL);
>>  
>>  	spin_lock_irqsave(&mem->spinlock, flags);
>> -	pos = (device_addr - mem->device_base) >> PAGE_SHIFT;
>> +	pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem));
>>  	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
>>  	spin_unlock_irqrestore(&mem->spinlock, flags);
>>  
>> @@ -186,7 +199,7 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
>>  	/*
>>  	 * Memory was found in the per-device area.
>>  	 */
>> -	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
>> +	*dma_handle = dma_get_device_base(dev, mem) + (pageno << PAGE_SHIFT);
>>  	*ret = mem->virt_base + (pageno << PAGE_SHIFT);
>>  	dma_memory_map = (mem->flags & DMA_MEMORY_MAP);
>>  	spin_unlock_irqrestore(&mem->spinlock, flags);
>>
> 
>