[PATCH] ASoC: rt5640: Handle 0Hz sysclk during stream shutdown

[Sheetal <sheetal@nvidia.com>]

Commit 2458adb8f92a ("SoC: simple-card-utils: set 0Hz to sysclk when
shutdown") sends a 0Hz sysclk request during stream shutdown to clear
codec rate constraints. The rt5640 codec forwards this 0Hz to
clk_set_rate(), which can cause clock controller firmware faults on
platforms where MCLK is SoC-driven (e.g. Tegra) and 0Hz falls below
the hardware minimum rate.

Handle the 0Hz case by clearing the internal sysclk state and
returning early, avoiding the invalid clk_set_rate() call.

Signed-off-by: Sheetal <sheetal@nvidia.com>
---
This is a follow-up to the discussion on the ignore_zero_sysclk flag:
https://patchwork.ozlabs.org/project/linux-tegra/patch/20260317094910.1582011-2-sheetal@nvidia.com/

Instead of adding a framework flag, handle 0Hz directly in the codec
as suggested by the reviewers.
---
 sound/soc/codecs/rt5640.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/soc/codecs/rt5640.c b/sound/soc/codecs/rt5640.c
index db2222e6f2e7..f6c6294e1588 100644
--- a/sound/soc/codecs/rt5640.c
+++ b/sound/soc/codecs/rt5640.c
@@ -1838,6 +1838,11 @@ static int rt5640_set_dai_sysclk(struct snd_soc_dai *dai,
 	unsigned int pll_bit = 0;
 	int ret;
 
+	if (!freq) {
+		rt5640->sysclk = 0;
+		return 0;
+	}
+
 	switch (clk_id) {
 	case RT5640_SCLK_S_MCLK:
 		ret = clk_set_rate(rt5640->mclk, freq);
-- 
2.17.1