Re: [PATCH v2 3/3] dmaengine: add union chan_dev for dma_chan::dev for clarity

On Thu, Sep 03, 2026 at 04:53:13PM -0400, Frank.Li@oss.nxp.com wrote:

The current dma_chan structure contains both "device" and "dev". So

chan->device->dev refers to the DMA engine device.
chan->dev->device refers to the per-channel device instance.

Their similar naming makes the distinction unclear and increases reader
confusion.

Add union dma_chan::chan_dev to make its purpose explicit and clearly
identify it as the per-channel device. After all user switch to chan_dev,
union and dma_chan::dev will be removed.

Update the kernel-doc accordingly. Besides its sysfs usage, the per-channel
device is also used by some DMA engine drivers for IOMMU mapping and
therefore deserves a more accurate description.

No functional change intended.

...

 static inline struct device *chan2dev(struct axi_dma_chan *chan)
 {
-	return &chan->vc.chan.dev->device;
+	return &chan->vc.chan.chan_dev->device;
 }

Looking at this and below I think we need a common helper(s)

 static struct device *chan2dev(struct loongson2_cmc_dma_chan *lchan)
 {
-	return &lchan->vchan.chan.dev->device;
+	return &lchan->vchan.chan.chan_dev->device;
 }

 	({								\
 		u32 _v;							\
 		_v = readl_relaxed((phy)->base + _reg((phy)->idx));	\
-		dev_vdbg(&phy->vchan->vc.chan.dev->device,		\
+		dev_vdbg(&phy->vchan->vc.chan.chan_dev->device,		\
 			 "%s(): readl(%s): 0x%08x\n", __func__, #_reg,	\
 			  _v);						\
 		_v;							\

 #define phy_writel(phy, val, _reg)					\
 	do {								\
 		writel((val), (phy)->base + _reg((phy)->idx));		\
-		dev_vdbg(&phy->vchan->vc.chan.dev->device,		\
+		dev_vdbg(&phy->vchan->vc.chan.chan_dev->device,		\
 			 "%s(): writel(0x%08x, %s)\n",			\
 			 __func__, (u32)(val), #_reg);			\
 	} while (0)
 #define phy_writel_relaxed(phy, val, _reg)				\
 	do {								\
 		writel_relaxed((val), (phy)->base + _reg((phy)->idx));	\
-		dev_vdbg(&phy->vchan->vc.chan.dev->device,		\
+		dev_vdbg(&phy->vchan->vc.chan.chan_dev->device,		\
 			 "%s(): writel_relaxed(0x%08x, %s)\n",		\
 			 __func__, (u32)(val), #_reg);			\
 	} while (0)

 out_unlock:
 	spin_unlock_irqrestore(&pdev->phy_lock, flags);
-	dev_dbg(&pchan->vc.chan.dev->device,
+	dev_dbg(&pchan->vc.chan.chan_dev->device,
 		"%s(): phy=%p(%d)\n", __func__, found,
 		found ? found->idx : -1);
 

-	dev_dbg(&chan->vc.chan.dev->device,
+	dev_dbg(&chan->vc.chan.chan_dev->device,
 		"%s(): freeing\n", __func__);

-	dev_dbg(&phy->vchan->vc.chan.dev->device,
+	dev_dbg(&phy->vchan->vc.chan.chan_dev->device,
 		"%s(); phy=%p(%d) misaligned=%d\n", __func__,
 		phy, phy->idx, misaligned);

-	dev_dbg(&phy->vchan->vc.chan.dev->device,
+	dev_dbg(&phy->vchan->vc.chan.chan_dev->device,
 		"%s(): phy=%p(%d)\n", __func__, phy, phy->idx);

-	dev_dbg(&chan->vc.chan.dev->device,
+	dev_dbg(&chan->vc.chan.chan_dev->device,
 		"%s(): desc=%p\n", __func__, desc);
 	if (!chan->phy) {
 		chan->phy = lookup_phy(chan);
 		if (!chan->phy) {
-			dev_dbg(&chan->vc.chan.dev->device,
+			dev_dbg(&chan->vc.chan.chan_dev->device,
 				"%s(): no free dma channel\n", __func__);
 			return;

(and so on in this PXA driver)

Besides that we should drop __func__ from all _dbg() messages, that can be
enabled run-time with help of Dynamic Debug.

So I think this driver requires more prerequisite work.

 static struct device *chan2dev(struct stm32_dma_chan *chan)
 {
-	return &chan->vchan.chan.dev->device;
+	return &chan->vchan.chan.chan_dev->device;
 }

 static struct device *chan2dev(struct stm32_dma3_chan *chan)
 {
-	return &chan->vchan.chan.dev->device;
+	return &chan->vchan.chan.chan_dev->device;
 }

 static struct device *chan2dev(struct stm32_mdma_chan *chan)
 {
-	return &chan->vchan.chan.dev->device;
+	return &chan->vchan.chan.chan_dev->device;
 }

...

Something like

vchan_to_device(vchan)
{
	return &vchan->chan.chan_dev->device;
}



-- 
With Best Regards,
Andy Shevchenko