Re: [PATCH v3] coresight: tmc-etr: Speed up for bounce buffer in flat mode

Hi Robin,

On Wed, Sep 01, 2021 at 09:03:30PM +0100, Robin Murphy wrote:

[...]

quoted

@@ -600,6 +601,7 @@ static int tmc_etr_alloc_flat_buf(struct tmc_drvdata *drvdata,
  {
  	struct etr_flat_buf *flat_buf;
  	struct device *real_dev = drvdata->csdev->dev.parent;
+	ssize_t	aligned_size;
  	/* We cannot reuse existing pages for flat buf */
  	if (pages)

@@ -609,11 +611,18 @@ static int tmc_etr_alloc_flat_buf(struct tmc_drvdata *drvdata,
  	if (!flat_buf)
  		return -ENOMEM;
-	flat_buf->vaddr = dma_alloc_coherent(real_dev, etr_buf->size,
-					     &flat_buf->daddr, GFP_KERNEL);
-	if (!flat_buf->vaddr) {
-		kfree(flat_buf);
-		return -ENOMEM;
+	aligned_size = PAGE_ALIGN(etr_buf->size);
+	flat_buf->pages = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO,
+					   get_order(aligned_size));
+	if (!flat_buf->pages)
+		goto fail_alloc_pages;
+
+	flat_buf->vaddr = page_address(flat_buf->pages);
+	flat_buf->daddr = dma_map_page(real_dev, flat_buf->pages, 0,
+				       aligned_size, DMA_FROM_DEVICE);

Use dma_alloc_noncoherent() rather than open-coding this - bare
alloc_pages() has no understanding of DMA masks, and you wouldn't want to
end up in the worst case of dma_map_page() bounce-buffering your bounce
buffer...

Will refine the code with dma_alloc_noncoherent(); it's much reliable
than the self writing code.

Thanks a lot for the suggestion!

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