Re: [PATCH 3/3] ALSA: qc_audio_offload: try to reduce address space confusion

[Takashi Iwai <tiwai@suse.de>]

On Tue, 16 Sep 2025 10:41:01 +0200,
Luca Weiss wrote:
> 
> Hi Arnd,
> 
> On Fri Sep 5, 2025 at 4:54 PM CEST, Arnd Bergmann wrote:
> > On Fri, Sep 5, 2025, at 14:26, Takashi Iwai wrote:
> >> On Fri, 05 Sep 2025 13:47:28 +0200,
> >
> >> @@ -1051,18 +1050,13 @@ static int uaudio_transfer_buffer_setup(struct 
> >> snd_usb_substream *subs,
> >>  	if (!xfer_buf)
> >>  		return -ENOMEM;
> >> 
> >> -	/* Remapping is not possible if xfer_buf is outside of linear map */
> >> -	xfer_buf_pa = virt_to_phys(xfer_buf);
> >> -	if (WARN_ON(!page_is_ram(PFN_DOWN(xfer_buf_pa)))) {
> >> -		ret = -ENXIO;
> >> -		goto unmap_sync;
> >> -	}
> >>  	dma_get_sgtable(subs->dev->bus->sysdev, &xfer_buf_sgt, xfer_buf,
> >>  			xfer_buf_dma, len);
> >> 
> >>  	/* map the physical buffer into sysdev as well */
> >> +	/* note: 0 is passed to pa argument as we use sgt */
> >>  	xfer_buf_dma_sysdev = uaudio_iommu_map(MEM_XFER_BUF, dma_coherent,
> >> -					       xfer_buf_pa, len, &xfer_buf_sgt);
> >> +					       0, len, &xfer_buf_sgt);
> >>  	if (!xfer_buf_dma_sysdev) {
> >>  		ret = -ENOMEM;
> >>  		goto unmap_sync;
> >
> >
> > Makes sense. I had to rework the code a little more to actually
> > understand how it fits together, for reference the below version
> > (I don't expect it to build cleanly) would split up
> > uaudio_iommu_map() into one function that takes a physical
> > address and another function that takes an sg table.
> 
> Are you planning to post this as a proper patch? It's a bit late in the
> 6.17 cycle already but good to still get this fixed for final release.
> 
> Or revert the original commit that broke it for now.
> 
> I couldn't really test your patch since there's a couple of compile
> errors where I wasn't sure how to resolve them correctly.

Could you check the patch below, then?  At least it compiles without
errors.


Takashi

--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -538,38 +538,33 @@ static void uaudio_iommu_unmap(enum mem_type mtype, unsigned long iova,
 			umap_size, iova, mapped_iova_size);
 }
 
+static int uaudio_iommu_map_prot(bool dma_coherent)
+{
+	int prot = IOMMU_READ | IOMMU_WRITE;
+
+	if (dma_coherent)
+		prot |= IOMMU_CACHE;
+	return prot;
+}
+
 /**
- * uaudio_iommu_map() - maps iommu memory for adsp
+ * uaudio_iommu_map_pa() - maps iommu memory for adsp
  * @mtype: ring type
  * @dma_coherent: dma coherent
  * @pa: physical address for ring/buffer
  * @size: size of memory region
- * @sgt: sg table for memory region
  *
  * Maps the XHCI related resources to a memory region that is assigned to be
  * used by the adsp.  This will be mapped to the domain, which is created by
  * the ASoC USB backend driver.
  *
  */
-static unsigned long uaudio_iommu_map(enum mem_type mtype, bool dma_coherent,
-				      phys_addr_t pa, size_t size,
-				      struct sg_table *sgt)
+static unsigned long uaudio_iommu_map_pa(enum mem_type mtype, bool dma_coherent,
+					 phys_addr_t pa, size_t size)
 {
-	struct scatterlist *sg;
 	unsigned long iova = 0;
-	size_t total_len = 0;
-	unsigned long iova_sg;
-	phys_addr_t pa_sg;
 	bool map = true;
-	size_t sg_len;
-	int prot;
-	int ret;
-	int i;
-
-	prot = IOMMU_READ | IOMMU_WRITE;
-
-	if (dma_coherent)
-		prot |= IOMMU_CACHE;
+	int prot = uaudio_iommu_map_prot(dma_coherent);
 
 	switch (mtype) {
 	case MEM_EVENT_RING:
@@ -583,20 +578,41 @@ static unsigned long uaudio_iommu_map(enum mem_type mtype, bool dma_coherent,
 				     &uaudio_qdev->xfer_ring_iova_size,
 				     &uaudio_qdev->xfer_ring_list, size);
 		break;
-	case MEM_XFER_BUF:
-		iova = uaudio_get_iova(&uaudio_qdev->curr_xfer_buf_iova,
-				     &uaudio_qdev->xfer_buf_iova_size,
-				     &uaudio_qdev->xfer_buf_list, size);
-		break;
 	default:
 		dev_err(uaudio_qdev->data->dev, "unknown mem type %d\n", mtype);
 	}
 
 	if (!iova || !map)
-		goto done;
+		return 0;
 
-	if (!sgt)
-		goto skip_sgt_map;
+	iommu_map(uaudio_qdev->data->domain, iova, pa, size, prot, GFP_KERNEL);
+
+	return iova;
+}
+
+static unsigned long uaudio_iommu_map_xfer_buf(bool dma_coherent, size_t size,
+					       struct sg_table *sgt)
+{
+	struct scatterlist *sg;
+	unsigned long iova = 0;
+	size_t total_len = 0;
+	unsigned long iova_sg;
+	phys_addr_t pa_sg;
+	size_t sg_len;
+	int prot = uaudio_iommu_map_prot(dma_coherent);
+	int ret;
+	int i;
+
+	prot = IOMMU_READ | IOMMU_WRITE;
+
+	if (dma_coherent)
+		prot |= IOMMU_CACHE;
+
+	iova = uaudio_get_iova(&uaudio_qdev->curr_xfer_buf_iova,
+			       &uaudio_qdev->xfer_buf_iova_size,
+			       &uaudio_qdev->xfer_buf_list, size);
+	if (!iova)
+		goto done;
 
 	iova_sg = iova;
 	for_each_sg(sgt->sgl, sg, sgt->nents, i) {
@@ -618,11 +634,6 @@ static unsigned long uaudio_iommu_map(enum mem_type mtype, bool dma_coherent,
 		uaudio_iommu_unmap(MEM_XFER_BUF, iova, size, total_len);
 		iova = 0;
 	}
-	return iova;
-
-skip_sgt_map:
-	iommu_map(uaudio_qdev->data->domain, iova, pa, size, prot, GFP_KERNEL);
-
 done:
 	return iova;
 }
@@ -1061,8 +1072,8 @@ static int uaudio_transfer_buffer_setup(struct snd_usb_substream *subs,
 			xfer_buf_dma, len);
 
 	/* map the physical buffer into sysdev as well */
-	xfer_buf_dma_sysdev = uaudio_iommu_map(MEM_XFER_BUF, dma_coherent,
-					       xfer_buf_pa, len, &xfer_buf_sgt);
+	xfer_buf_dma_sysdev = uaudio_iommu_map_xfer_buf(dma_coherent,
+							len, &xfer_buf_sgt);
 	if (!xfer_buf_dma_sysdev) {
 		ret = -ENOMEM;
 		goto unmap_sync;
@@ -1143,8 +1154,8 @@ uaudio_endpoint_setup(struct snd_usb_substream *subs,
 	sg_free_table(sgt);
 
 	/* data transfer ring */
-	iova = uaudio_iommu_map(MEM_XFER_RING, dma_coherent, tr_pa,
-			      PAGE_SIZE, NULL);
+	iova = uaudio_iommu_map_pa(MEM_XFER_RING, dma_coherent, tr_pa,
+				   PAGE_SIZE);
 	if (!iova) {
 		ret = -ENOMEM;
 		goto clear_pa;
@@ -1207,8 +1218,8 @@ static int uaudio_event_ring_setup(struct snd_usb_substream *subs,
 	mem_info->dma = sg_dma_address(sgt->sgl);
 	sg_free_table(sgt);
 
-	iova = uaudio_iommu_map(MEM_EVENT_RING, dma_coherent, er_pa,
-			      PAGE_SIZE, NULL);
+	iova = uaudio_iommu_map_pa(MEM_EVENT_RING, dma_coherent, er_pa,
+				   PAGE_SIZE);
 	if (!iova) {
 		ret = -ENOMEM;
 		goto clear_pa;