omap: Fix race condition in omap dma driver

The bug could cause irq enable bit of one DMA channel is
cleared/set unexpectedly when 2 (or more) drivers are calling
omap_request_dma()/omap_free_dma() simultaneously

Signed-off-by: Fei Yang <[e-mail]>
Signed-off-by: Tao Hu <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/plat-omap/dma.c

···
 static inline void omap2_enable_irq_lch(int lch)
 {
 	u32 val;
+	unsigned long flags;
 
 	if (!cpu_class_is_omap2())
 		return;
 
+	spin_lock_irqsave(&dma_chan_lock, flags);
 	val = dma_read(IRQENABLE_L0);
 	val |= 1 << lch;
 	dma_write(val, IRQENABLE_L0);
+	spin_unlock_irqrestore(&dma_chan_lock, flags);
 }
 
 int omap_request_dma(int dev_id, const char *dev_name,
···
 
 	if (cpu_class_is_omap2()) {
 		u32 val;
+
+		spin_lock_irqsave(&dma_chan_lock, flags);
 		/* Disable interrupts */
 		val = dma_read(IRQENABLE_L0);
 		val &= ~(1 << lch);
 		dma_write(val, IRQENABLE_L0);
+		spin_unlock_irqrestore(&dma_chan_lock, flags);
 
 		/* Clear the CSR register and IRQ status register */
 		dma_write(OMAP2_DMA_CSR_CLEAR_MASK, CSR(lch));