ALSA: hda: Workaround for SDnCTL register on loongson

On loongson controller, after calling snd_hdac_stream_updateb()
to enable DMA engine, the SDnCTL.STRM will become to zero.  We
need to access SDnCTL in dword to keep SDnCTL.STRM is not changed.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Yingkun Meng <mengyingkun@loongson.cn>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/r/27aeddf5ebbe7c69631cec0e489c1b264be94990.1686128807.git.siyanteng@loongson.cn
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: Yanteng Si

include/sound/hdaudio.h

@@ -348,6 +348,7 @@ struct hdac_bus {
 	bool polling_mode:1;
 	bool needs_damn_long_delay:1;
 	bool not_use_interrupts:1;	/* prohibiting the RIRB IRQ */
+	bool access_sdnctl_in_dword:1;	/* accessing the sdnctl register by dword */
 
 	int poll_count;
 

sound/hda/hdac_stream.c

@@ -150,7 +150,11 @@ void snd_hdac_stream_start(struct hdac_stream *azx_dev)
 					stripe_ctl);
 	}
 	/* set DMA start and interrupt mask */
-	snd_hdac_stream_updateb(azx_dev, SD_CTL,
+	if (bus->access_sdnctl_in_dword)
+		snd_hdac_stream_updatel(azx_dev, SD_CTL,
+				0, SD_CTL_DMA_START | SD_INT_MASK);
+	else
+		snd_hdac_stream_updateb(azx_dev, SD_CTL,
 				0, SD_CTL_DMA_START | SD_INT_MASK);
 	azx_dev->running = true;
 }

sound/pci/hda/hda_intel.c

@@ -1878,6 +1878,7 @@ static int azx_first_init(struct azx *chip)
 	if (chip->driver_type == AZX_DRIVER_LOONGSON) {
 		bus->polling_mode = 1;
 		bus->not_use_interrupts = 1;
+		bus->access_sdnctl_in_dword = 1;
 	}
 
 	err = pcim_iomap_regions(pci, 1 << 0, "ICH HD audio");