ASoC: rsnd: control SSICR::EN correctly

In case of SSI0 playback, SSI1 capture, SSI0 might be shared for
clock output if clock master mode.

Current rsnd driver had been assumed that SSI clock contiguous
output which is needed for SSI parent needs SSICR::EN (SSI module
enable) bit.
But, this bit controls data input/output, not for clock.
Clock contiguous output needs SSICR : FORCE, SCKD, SWSD,
and SSIWSR : CONT. Not SSICR : EN.

Because of this wrong assumption, and insufficient control, on current
code, for example, if it starts SSI0(playback) -> SSI1(capture) order,
SSI0 SSICR::EN bit will temporarily be 0.
It causes playback side underrun error. This is bug.
We can reproduce this issue with SSI+SRC (without DVC), and capture
during playback operation.

This patch fixup current (wrong) assumption, and control SSICR::EN bit
correctly.
Reported-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rcar/ssi.c

@@ -72,6 +72,7 @@ struct rsnd_ssi {
 	u32 cr_own;
 	u32 cr_clk;
 	u32 cr_mode;
+	u32 cr_en;
 	u32 wsr;
 	int chan;
 	int rate;
@@ -291,6 +292,16 @@ static int rsnd_ssi_master_clk_start(struct rsnd_mod *mod,
 	if (ret < 0)
 		return ret;
 
+	/*
+	 * SSI clock will be output contiguously
+	 * by below settings.
+	 * This means, rsnd_ssi_master_clk_start()
+	 * and rsnd_ssi_register_setup() are necessary
+	 * for SSI parent
+	 *
+	 * SSICR  : FORCE, SCKD, SWSD
+	 * SSIWSR : CONT
+	 */
 	ssi->cr_clk = FORCE | SWL_32 | SCKD | SWSD | CKDV(idx);
 	ssi->wsr = CONT;
 	ssi->rate = rate;
@@ -393,7 +404,8 @@ static void rsnd_ssi_register_setup(struct rsnd_mod *mod)
 	rsnd_mod_write(mod, SSIWSR,	ssi->wsr);
 	rsnd_mod_write(mod, SSICR,	ssi->cr_own	|
 					ssi->cr_clk	|
-					ssi->cr_mode); /* without EN */
+					ssi->cr_mode	|
+					ssi->cr_en);
 }
 
 static void rsnd_ssi_pointer_init(struct rsnd_mod *mod,
@@ -544,6 +556,8 @@ static int rsnd_ssi_start(struct rsnd_mod *mod,
 			  struct rsnd_dai_stream *io,
 			  struct rsnd_priv *priv)
 {
+	struct rsnd_ssi *ssi = rsnd_mod_to_ssi(mod);
+
 	if (!rsnd_ssi_is_run_mods(mod, io))
 		return 0;
 
@@ -554,7 +568,19 @@ static int rsnd_ssi_start(struct rsnd_mod *mod,
 	if (rsnd_ssi_multi_slaves_runtime(io))
 		return 0;
 
-	rsnd_mod_bset(mod, SSICR, EN, EN);
+	/*
+	 * EN is for data output.
+	 * SSI parent EN is not needed.
+	 */
+	if (rsnd_ssi_is_parent(mod, io))
+		return 0;
+
+	ssi->cr_en = EN;
+
+	rsnd_mod_write(mod, SSICR,	ssi->cr_own	|
+					ssi->cr_clk	|
+					ssi->cr_mode	|
+					ssi->cr_en);
 
 	return 0;
 }
@@ -569,13 +595,7 @@ static int rsnd_ssi_stop(struct rsnd_mod *mod,
 	if (!rsnd_ssi_is_run_mods(mod, io))
 		return 0;
 
-	/*
-	 * don't stop if not last user
-	 * see also
-	 *	rsnd_ssi_start
-	 *	rsnd_ssi_interrupt
-	 */
-	if (ssi->usrcnt > 1)
+	if (rsnd_ssi_is_parent(mod, io))
 		return 0;
 
 	/*
@@ -595,6 +615,8 @@ static int rsnd_ssi_stop(struct rsnd_mod *mod,
 	rsnd_mod_write(mod, SSICR, cr);	/* disabled all */
 	rsnd_ssi_status_check(mod, IIRQ);
 
+	ssi->cr_en = 0;
+
 	return 0;
 }