ASoC: sh: rz-ssi: Improve error handling in rz_ssi_dma_request function

dma_request_chan() returns error pointer in case of failures, but
the rz_ssi_dma_request() checked for NULL pointer instead.

This patch fixes the issue by checking for ERR_PTR() instead of
NULL and sets the DMA pointers to NULL in error case so that ssi
can fallback to PIO mode.

Fixes: 26ac471c53 ("ASoC: sh: rz-ssi: Add SSI DMAC support")
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20210818101450.15948-1-biju.das.jz@bp.renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rz-ssi.c

@@ -185,7 +185,7 @@ rz_ssi_stream_get(struct rz_ssi_priv *ssi, struct snd_pcm_substream *substream)
 
 static inline bool rz_ssi_is_dma_enabled(struct rz_ssi_priv *ssi)
 {
-	return (ssi->playback.dma_ch || ssi->capture.dma_ch);
+	return (ssi->playback.dma_ch && (ssi->dma_rt || ssi->capture.dma_ch));
 }
 
 static int rz_ssi_stream_is_valid(struct rz_ssi_priv *ssi,
@@ -676,15 +676,26 @@ static void rz_ssi_release_dma_channels(struct rz_ssi_priv *ssi)
 static int rz_ssi_dma_request(struct rz_ssi_priv *ssi, struct device *dev)
 {
 	ssi->playback.dma_ch = dma_request_chan(dev, "tx");
+	if (IS_ERR(ssi->playback.dma_ch))
+		ssi->playback.dma_ch = NULL;
+
 	ssi->capture.dma_ch = dma_request_chan(dev, "rx");
+	if (IS_ERR(ssi->capture.dma_ch))
+		ssi->capture.dma_ch = NULL;
+
 	if (!ssi->playback.dma_ch && !ssi->capture.dma_ch) {
 		ssi->playback.dma_ch = dma_request_chan(dev, "rt");
-		if (!ssi->playback.dma_ch)
+		if (IS_ERR(ssi->playback.dma_ch)) {
+			ssi->playback.dma_ch = NULL;
 			goto no_dma;
+		}
 
 		ssi->dma_rt = true;
 	}
 
+	if (!rz_ssi_is_dma_enabled(ssi))
+		goto no_dma;
+
 	if (ssi->playback.dma_ch &&
 	    (rz_ssi_dma_slave_config(ssi, ssi->playback.dma_ch, true) < 0))
 		goto no_dma;