ALSA: memalloc: Drop x86-specific hack for WC allocations

The recent report for a crash on Haswell machines implied that the
x86-specific (rather hackish) implementation for write-cache memory
buffer allocation in ALSA core is buggy with the recent kernel in some
corner cases.  This patch drops the x86-specific implementation and
uses the standard dma_alloc_wc() & co generically for avoiding the bug
and also for simplification.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=216112
Cc: <stable@vger.kernel.org> # v5.18+
Link: https://lore.kernel.org/r/20220620073440.7514-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/memalloc.c

@@ -431,33 +431,17 @@ static const struct snd_malloc_ops snd_dma_iram_ops = {
  */
 static void *snd_dma_dev_alloc(struct snd_dma_buffer *dmab, size_t size)
 {
-	void *p;
-
-	p = dma_alloc_coherent(dmab->dev.dev, size, &dmab->addr, DEFAULT_GFP);
-#ifdef CONFIG_X86
-	if (p && dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC)
-		set_memory_wc((unsigned long)p, PAGE_ALIGN(size) >> PAGE_SHIFT);
-#endif
-	return p;
+	return dma_alloc_coherent(dmab->dev.dev, size, &dmab->addr, DEFAULT_GFP);
 }
 
 static void snd_dma_dev_free(struct snd_dma_buffer *dmab)
 {
-#ifdef CONFIG_X86
-	if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC)
-		set_memory_wb((unsigned long)dmab->area,
-			      PAGE_ALIGN(dmab->bytes) >> PAGE_SHIFT);
-#endif
 	dma_free_coherent(dmab->dev.dev, dmab->bytes, dmab->area, dmab->addr);
 }
 
 static int snd_dma_dev_mmap(struct snd_dma_buffer *dmab,
 			    struct vm_area_struct *area)
 {
-#ifdef CONFIG_X86
-	if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC)
-		area->vm_page_prot = pgprot_writecombine(area->vm_page_prot);
-#endif
 	return dma_mmap_coherent(dmab->dev.dev, area,
 				 dmab->area, dmab->addr, dmab->bytes);
 }
@@ -471,10 +455,6 @@ static const struct snd_malloc_ops snd_dma_dev_ops = {
 /*
  * Write-combined pages
  */
-#ifdef CONFIG_X86
-/* On x86, share the same ops as the standard dev ops */
-#define snd_dma_wc_ops	snd_dma_dev_ops
-#else /* CONFIG_X86 */
 static void *snd_dma_wc_alloc(struct snd_dma_buffer *dmab, size_t size)
 {
 	return dma_alloc_wc(dmab->dev.dev, size, &dmab->addr, DEFAULT_GFP);
@@ -497,7 +477,6 @@ static const struct snd_malloc_ops snd_dma_wc_ops = {
 	.free = snd_dma_wc_free,
 	.mmap = snd_dma_wc_mmap,
 };
-#endif /* CONFIG_X86 */
 
 #ifdef CONFIG_SND_DMA_SGBUF
 static void *snd_dma_sg_fallback_alloc(struct snd_dma_buffer *dmab, size_t size);