Re: [PATCH 22/28] sgiseeq: convert from dma_cache_sync to dma_sync_single_for_device

On Wed, Sep 02, 2020 at 11:38:09PM +0200, Thomas Bogendoerfer wrote:

the patch below fixes the problem.

But is very wrong unfortunately.

 static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
 {
-       dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
-                      DMA_FROM_DEVICE);
+       struct sgiseeq_private *sp = netdev_priv(dev);
+
+       dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
+                       sizeof(struct sgiseeq_rx_desc), DMA_FROM_DEVICE);
 }
 
 static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
 {
-       dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
-                      DMA_TO_DEVICE);
+       struct sgiseeq_private *sp = netdev_priv(dev);
+
+       dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
+                       sizeof(struct sgiseeq_rx_desc), DMA_TO_DEVICE);

This is not how the DMA API works.  You can only call
dma_sync_single_for_{device,cpu} with the direction that the memory
was mapped.  It then transfer ownership to the device or the cpu,
and the ownership of the memory is a fundamental concept that allows
for reasoning about the caching interaction.

 }
 
-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

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