gpu: host1x: Use correct semantics for HOST1X_CHANNEL_DMAEND

The HOST1X_CHANNEL_DMAEND is an offset relative to the value written to
the HOST1X_CHANNEL_DMASTART register, but it is currently treated as an
absolute address. This can cause SMMU faults if the CDMA fetches past a
pushbuffer's IOMMU mapping.

Properly setting the DMAEND prevents the CDMA from fetching beyond that
address and avoid such issues. This is currently not observed because a
whole (almost) page of essentially scratch space absorbs any excessive
prefetching by CDMA. However, changing the number of slots in the push
buffer can trigger these SMMU faults.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/host1x/hw/cdma_hw.c

@@ -75,7 +75,7 @@ static void cdma_start(struct host1x_cdma *cdma)
 
 	cdma->last_pos = cdma->push_buffer.pos;
 	start = cdma->push_buffer.dma;
-	end = start + cdma->push_buffer.size + 4;
+	end = cdma->push_buffer.size + 4;
 
 	host1x_ch_writel(ch, HOST1X_CHANNEL_DMACTRL_DMASTOP,
 			 HOST1X_CHANNEL_DMACTRL);
@@ -126,7 +126,7 @@ static void cdma_timeout_restart(struct host1x_cdma *cdma, u32 getptr)
 			 HOST1X_CHANNEL_DMACTRL);
 
 	start = cdma->push_buffer.dma;
-	end = start + cdma->push_buffer.size + 4;
+	end = cdma->push_buffer.size + 4;
 
 	/* set base, end pointer (all of memory) */
 	host1x_ch_writel(ch, lower_32_bits(start), HOST1X_CHANNEL_DMASTART);