Add driver for SAMA7G5's PDMC

Merge series from Codrin Ciubotariu <codrin.ciubotariu@microchip.com>:

This patch series adds support for Pulse Density Microphone Controller
(PDMC), present on Microchip's SAMA7G5.
The PDMC interfaces up to 4 digital microphones having Pulse Density
Modulated (PDM) outputs. It generates a single clock line and samples 1 or
2 data lines. The signal path includes an audio grade programmable
decimation filter and outputs 24-bit audio words.
The source of each channel can be independently defined as PDMC_DS0 or
PDMC_DS1, sampled at the rising or falling edge of PDMC_CLK.

The patch series starts with a fix on the ASoC DMA engine support. Then
continues with the bindings and the driver of PDMC. It is followed by the
DT nodes for SAMA7G5 and SAMA7G5-EK. In the end, the drivers for PDMC
and PDM microphones are enabled in sama7_defconfig.

Documentation/devicetree/bindings/sound/microchip,pdmc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/microchip,pdmc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip Pulse Density Microphone Controller
+
+maintainers:
+  - Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
+
+description:
+  The Microchip Pulse Density Microphone Controller (PDMC) interfaces up to 4
+  digital microphones having Pulse Density Modulated (PDM) outputs.
+
+properties:
+  compatible:
+    const: microchip,sama7g5-pdmc
+
+  reg:
+    maxItems: 1
+
+  "#sound-dai-cells":
+    const: 0
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    items:
+      - description: Peripheral Bus Clock
+      - description: Generic Clock
+
+  clock-names:
+    items:
+      - const: pclk
+      - const: gclk
+
+  dmas:
+    description: RX DMA Channel
+    maxItems: 1
+
+  dma-names:
+    const: rx
+
+  microchip,mic-pos:
+    description: |
+      Position of PDM microphones on the DS line and the sampling edge (rising
+      or falling) of the CLK line. A microphone is represented as a pair of DS
+      line and the sampling edge. The first microphone is mapped to channel 0,
+      the second to channel 1, etc.
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    items:
+      items:
+        - description: value for DS line
+        - description: value for sampling edge
+      anyOf:
+        - enum:
+            - [0, 0]
+            - [0, 1]
+            - [1, 0]
+            - [1, 1]
+    minItems: 1
+    maxItems: 4
+    uniqueItems: true
+
+required:
+  - compatible
+  - reg
+  - "#sound-dai-cells"
+  - interrupts
+  - clocks
+  - clock-names
+  - dmas
+  - dma-names
+  - microchip,mic-pos
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/at91.h>
+    #include <dt-bindings/dma/at91.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/sound/microchip,pdmc.h>
+
+    pdmc: sound@e1608000 {
+        compatible = "microchip,sama7g5-pdmc";
+        reg = <0xe1608000 0x4000>;
+        #sound-dai-cells = <0>;
+        interrupts = <GIC_SPI 68 IRQ_TYPE_LEVEL_HIGH>;
+        dmas = <&dma0 AT91_XDMAC_DT_PERID(37)>;
+        dma-names = "rx";
+        clocks = <&pmc PMC_TYPE_PERIPHERAL 68>, <&pmc PMC_TYPE_GCK 68>;
+        clock-names = "pclk", "gclk";
+        microchip,mic-pos = <MCHP_PDMC_DS0 MCHP_PDMC_CLK_POSITIVE>,
+                            <MCHP_PDMC_DS0 MCHP_PDMC_CLK_NEGATIVE>,
+                            <MCHP_PDMC_DS1 MCHP_PDMC_CLK_POSITIVE>,
+                            <MCHP_PDMC_DS1 MCHP_PDMC_CLK_NEGATIVE>;
+    };

include/dt-bindings/sound/microchip,pdmc.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DT_BINDINGS_MICROCHIP_PDMC_H__
+#define __DT_BINDINGS_MICROCHIP_PDMC_H__
+
+/* PDM microphone's pin placement */
+#define MCHP_PDMC_DS0 0
+#define MCHP_PDMC_DS1 1
+
+/* PDM microphone clock edge sampling */
+#define MCHP_PDMC_CLK_POSITIVE 0
+#define MCHP_PDMC_CLK_NEGATIVE 1
+
+#endif /* __DT_BINDINGS_MICROCHIP_PDMC_H__ */

sound/soc/atmel/Kconfig

@@ -160,4 +160,20 @@ config SND_MCHP_SOC_SPDIFRX
 
 	  This S/PDIF RX driver is compliant with IEC-60958 standard and
 	  includes programmable User Data and Channel Status fields.
+
+config SND_MCHP_SOC_PDMC
+	tristate "Microchip ASoC driver for boards using PDMC"
+	depends on OF && (ARCH_AT91 || COMPILE_TEST)
+	select SND_SOC_GENERIC_DMAENGINE_PCM
+	select REGMAP_MMIO
+	help
+	  Say Y or M if you want to add support for Microchip ASoC PDMC driver on the
+	  following Microchip platforms:
+	  - sama7g5
+
+	  The Pulse Density Microphone Controller (PDMC) interfaces up to 4 digital
+	  microphones PDM outputs. It generates a single clock line and samples 1 or
+	  2 data lines. The signal path includes an audio grade programmable
+	  decimation filter and outputs 24-bit audio words.
+
 endif

sound/soc/atmel/Makefile

@@ -7,6 +7,7 @@ snd-soc-atmel-i2s-objs := atmel-i2s.o
 snd-soc-mchp-i2s-mcc-objs := mchp-i2s-mcc.o
 snd-soc-mchp-spdiftx-objs := mchp-spdiftx.o
 snd-soc-mchp-spdifrx-objs := mchp-spdifrx.o
+snd-soc-mchp-pdmc-objs := mchp-pdmc.o
 
 # pdc and dma need to both be built-in if any user of
 # ssc is built-in.
@@ -21,6 +22,7 @@ obj-$(CONFIG_SND_ATMEL_SOC_I2S) += snd-soc-atmel-i2s.o
 obj-$(CONFIG_SND_MCHP_SOC_I2S_MCC) += snd-soc-mchp-i2s-mcc.o
 obj-$(CONFIG_SND_MCHP_SOC_SPDIFTX) += snd-soc-mchp-spdiftx.o
 obj-$(CONFIG_SND_MCHP_SOC_SPDIFRX) += snd-soc-mchp-spdifrx.o
+obj-$(CONFIG_SND_MCHP_SOC_PDMC) += snd-soc-mchp-pdmc.o
 
 # AT91 Machine Support
 snd-soc-sam9g20-wm8731-objs := sam9g20_wm8731.o

sound/soc/soc-generic-dmaengine-pcm.c

@@ -86,10 +86,10 @@ static int dmaengine_pcm_hw_params(struct snd_soc_component *component,
 
 	memset(&slave_config, 0, sizeof(slave_config));
 
-	if (!pcm->config)
-		prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
-	else
+	if (pcm->config && pcm->config->prepare_slave_config)
 		prepare_slave_config = pcm->config->prepare_slave_config;
+	else
+		prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
 
 	if (prepare_slave_config) {
 		int ret = prepare_slave_config(substream, params, &slave_config);