ASoC: rockchip: add Serial Audio Interface (SAI) driver

The Rockchip RK3576 SoC features a new audio controller, the Serial
Audio Interface, or SAI for short. It is capable of both sending and
receiving audio over up to 4 lanes for each direction using the I2S,
PCM or TDM formats.

This driver is derived from the downstream vendor driver. That is why
its original author, Sugar Zhang, is listed as a Co-developer, with
their signoff. Since adjustments to make the driver suitable for
upstream were quite extensive, I've added myself to the authors and put
myself as the commit author; all added bugs are my fault alone, and not
that of the original author at Rockchip.

The hardware is somewhat similar to the Rockchip I2S-TDM hardware when
judged based on their register map, except it uses the same mclk for
tx and rx. It appears to be much more flexible with regards to TDM.
The loopback stuff and mono mode are new as well.

In line with the changes that were made to the Rockchip I2S-TDM driver
after upstreaming, the mclk-calibrate functionality was dropped, and
setting the mclk rate properly is now left up to the Common Clock
Framework, similar to how it is in the upstream I2S-TDM driver now.

A spinlock has been introduced to protect register write accesses that
depend on the bclk/fs to be stopped, i.e. XFER[1:0] being 0. I couldn't
find whether the asoc core held a per-instance lock so only one callback
can run at a time, and so it seemed prudent to add this.

I couldn't successfully test whether TDM was working, though I've tried
with a TAS6424 codec board. I'm not sure yet whether to blame the codec
driver, this version of the SAI driver, or the vendor implementation of
the SAI driver. The TDM mask registers remain untouched in both this
version and the downstream vendor version, which is suspicious, though
the Linux ASoC core wouldn't be able to support the 128 (!!!) slots of
TDM the hardware supports anyway.

Regular old 2-channel stereo I2S thrown at an I2S stereo codec works
well though. I tested with the CPU-side SAI controller in provider mode
and an Everest ES8388 codec as the consumer.

Some vendor driver features (no-dmaengine, fifo rockchip performance
monitoring, many kcontrols) were dropped for this initial upstream
version. They can always be added later if they make sense for upstream.

Co-developed-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Link: https://patch.msgid.link/20250410-rk3576-sai-v2-6-c64608346be3@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Nicolas Frattaroli

MAINTAINERS

@@ -20918,6 +20918,7 @@ M:	Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
 L:	linux-rockchip@lists.infradead.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/sound/rockchip,rk3576-sai.yaml
+F:	sound/soc/rockchip/rockchip_sai.*
 
 ROCKCHIP VIDEO DECODER DRIVER
 M:	Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

sound/soc/rockchip/Kconfig

@@ -37,6 +37,16 @@ config SND_SOC_ROCKCHIP_PDM
 	  Rockchip PDM Controller. The Controller supports up to maximum of
 	  8 channels record.
 
+config SND_SOC_ROCKCHIP_SAI
+	tristate "Rockchip SAI Controller Driver"
+	depends on HAVE_CLK && SND_SOC_ROCKCHIP
+	select SND_SOC_GENERIC_DMAENGINE_PCM
+	help
+	  Say Y or M if you want to add support for the Rockchip Serial Audio
+	  Interface controller found on Rockchip SoCs such as the RK3576. The
+	  controller may support both playback and recording, with up to 4 lanes
+	  for each and up to 128 channels per lane in TDM mode.
+
 config SND_SOC_ROCKCHIP_SPDIF
 	tristate "Rockchip SPDIF Device Driver"
 	depends on HAVE_CLK && SND_SOC_ROCKCHIP

sound/soc/rockchip/Makefile

@@ -3,10 +3,12 @@
 snd-soc-rockchip-i2s-y := rockchip_i2s.o
 snd-soc-rockchip-i2s-tdm-y := rockchip_i2s_tdm.o
 snd-soc-rockchip-pdm-y := rockchip_pdm.o
+snd-soc-rockchip-sai-y := rockchip_sai.o
 snd-soc-rockchip-spdif-y := rockchip_spdif.o
 
 obj-$(CONFIG_SND_SOC_ROCKCHIP_I2S) += snd-soc-rockchip-i2s.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_PDM) += snd-soc-rockchip-pdm.o
+obj-$(CONFIG_SND_SOC_ROCKCHIP_SAI) += snd-soc-rockchip-sai.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_SPDIF) += snd-soc-rockchip-spdif.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_I2S_TDM) += snd-soc-rockchip-i2s-tdm.o