[PATCH 2/2] usb: gadget: f_uac2: allow explicit channel counts

USB Audio 2.0 permits bNrChannels to be specified independently of
bmChannelConfig. In particular, a zero channel-location bitmap indicates
that all channels have non-predefined spatial positions. f_uac2 currently
derives bNrChannels from the number of bits set in bmChannelConfig. Since
the channel-location bitmap provides only 27 predefined speaker positions,
this limits a stream to 27 channels.

Preserve the existing *_chmask interface and semantics by introducing
separate ConfigFS attributes for explicit channel counts. Add p_channels
and c_channels configfs attributes to configure the playback and capture
channel counts explicitly. A value of zero, which is the default, continues
to derive the channel count from the corresponding channel mask. The
explicit count is represented by the 8-bit bNrChannels field, allowing
channel counts beyond the 27 predefined locations and up to the UAC2 limit
of 255.

Use the effective channel count throughout descriptor generation and stream
configuration while continuing to populate bmChannelConfig directly from
the configured channel mask.

To keep the ConfigFS interface simple, require a nonzero channel mask to
describe every channel when an explicit channel count is also specified.
Partial channel-location assignments permitted by the UAC2 specification
are therefore not supported. Also reject Feature Unit configurations whose
descriptor length would exceed the one-byte bLength field.

Signed-off-by: Kyle Farrell <[email protected]>
---
 .../ABI/testing/configfs-usb-gadget-uac2      | 18 ++++-
 Documentation/usb/gadget-testing.rst          | 18 ++++-
 drivers/usb/gadget/function/f_uac2.c          | 71 +++++++++++++------
 drivers/usb/gadget/function/u_uac2.h          |  4 ++
 4 files changed, 87 insertions(+), 24 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uac2 b/Documentation/ABI/testing/configfs-usb-gadget-uac2
index 133e995c3e92..8e264843e492 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uac2
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uac2
@@ -5,7 +5,14 @@ Description:
 		The attributes:
 
 		=====================	=======================================
-		c_chmask		capture channel mask
+		c_chmask		capture channel-location mask. The number of
+					capture channels is derived from the number of
+					set bits unless c_channels is specified.
+		c_channels		explicit capture channel count. A value of 0
+					derives the channel count from c_chmask. When
+					nonzero, c_chmask specifies channel locations
+					and may be 0. If both c_channels and c_chmask
+					are nonzero, the values must agree.
 		c_srate			list of capture sampling rates (comma-separated)
 		c_ssize			capture sample size (bytes)
 		c_hs_bint		capture bInterval for HS/SS (1-4: fixed, 0: auto)
@@ -20,7 +27,14 @@ Description:
 		c_volume_res		capture volume control resolution
 					(in 1/256 dB)
 		fb_max			maximum extra bandwidth in async mode
-		p_chmask		playback channel mask
+		p_chmask		playback channel-location mask. The number of
+					playback channels is derived from the number of
+					set bits unless p_channels is specified.
+		p_channels		explicit playback channel count. A value of 0
+					derives the channel count from p_chmask. When
+					nonzero, p_chmask specifies channel locations
+					and may be 0. If both p_channels and p_chmask
+					are nonzero, the values must agree.
 		p_srate			list of playback sampling rates (comma-separated)
 		p_ssize			playback sample size (bytes)
 		p_hs_bint		playback bInterval for HS/SS (1-4: fixed, 0: auto)
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index a6e8292f320a..8fa778a2ed15 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -744,7 +744,14 @@ The function name to use when creating the function directory is "uac2".
 The uac2 function provides these attributes in its function directory:
 
 	================ ====================================================
-	c_chmask         capture channel mask
+	c_chmask         capture channel-location mask. The number of
+			 capture channels is derived from the number of
+			 set bits unless c_channels is specified.
+	c_channels	 explicit capture channel count. A value of 0
+			 derives the channel count from c_chmask. When
+			 nonzero, c_chmask specifies channel locations
+			 and may be 0. If both c_channels and c_chmask
+			 are nonzero, the values must agree.
 	c_srate          list of capture sampling rates (comma-separated)
 	c_ssize          capture sample size (bytes)
 	c_sync           capture synchronization type (async/adaptive)
@@ -755,7 +762,14 @@ The uac2 function provides these attributes in its function directory:
 	c_volume_res     capture volume control resolution (in 1/256 dB)
 	c_hs_bint        capture bInterval for HS/SS (1-4: fixed, 0: auto)
 	fb_max           maximum extra bandwidth in async mode
-	p_chmask         playback channel mask
+	p_chmask         playback channel-location mask. The number of
+			 playback channels is derived from the number of
+			 set bits unless p_channels is specified.
+	p_channels	 explicit playback channel count. A value of 0
+			 derives the channel count from p_chmask. When
+			 nonzero, p_chmask specifies channel locations
+			 and may be 0. If both p_channels and p_chmask
+			 are nonzero, the values must agree.
 	p_srate          list of playback sampling rates (comma-separated)
 	p_ssize          playback sample size (bytes)
 	p_mute_present   playback mute control enable
diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index b8735b9065c3..fab4c5bcb11b 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -50,8 +50,17 @@
 #define UNFLW_CTRL	8
 #define OVFLW_CTRL	10
 
-#define EPIN_EN(_opts) ((_opts)->p_chmask != 0)
-#define EPOUT_EN(_opts) ((_opts)->c_chmask != 0)
+static unsigned int uac2_num_channels(bool is_playback,
+				      const struct f_uac2_opts *opts)
+{
+	u8 channels = is_playback ? opts->p_channels : opts->c_channels;
+	u32 chmask = is_playback ? opts->p_chmask : opts->c_chmask;
+
+	return channels ? channels : num_channels(chmask);
+}
+
+#define EPIN_EN(_opts) (uac2_num_channels(true, (_opts)) != 0)
+#define EPOUT_EN(_opts) (uac2_num_channels(false, (_opts)) != 0)
 #define FUIN_EN(_opts) (EPIN_EN(_opts) \
 				&& ((_opts)->p_mute_present \
 				|| (_opts)->p_volume_present))
@@ -671,15 +680,16 @@ static int get_max_srate(const int *srates)
 static int get_max_bw_for_bint(const struct f_uac2_opts *uac2_opts,
 	u8 bint, unsigned int factor, bool is_playback)
 {
-	int chmask, srate, ssize;
+	unsigned int channels;
+	int srate, ssize;
 	u16 max_size_bw;
 
 	if (is_playback) {
-		chmask = uac2_opts->p_chmask;
+		channels = uac2_num_channels(true, uac2_opts);
 		srate = get_max_srate(uac2_opts->p_srates);
 		ssize = uac2_opts->p_ssize;
 	} else {
-		chmask = uac2_opts->c_chmask;
+		channels = uac2_num_channels(false, uac2_opts);
 		srate = get_max_srate(uac2_opts->c_srates);
 		ssize = uac2_opts->c_ssize;
 	}
@@ -689,11 +699,11 @@ static int get_max_bw_for_bint(const struct f_uac2_opts *uac2_opts,
 		// Win10 requires max packet size + 1 frame
 		srate = srate * (1000 + uac2_opts->fb_max) / 1000;
 		// updated srate is always bigger, therefore DIV_ROUND_UP always yields +1
-		max_size_bw = num_channels(chmask) * ssize *
+		max_size_bw = channels * ssize *
 			(DIV_ROUND_UP(srate, factor / (1 << (bint - 1))));
 	} else {
 		// adding 1 frame provision for Win10
-		max_size_bw = num_channels(chmask) * ssize *
+		max_size_bw = channels * ssize *
 			(DIV_ROUND_UP(srate, factor / (1 << (bint - 1))) + 1);
 	}
 	return max_size_bw;
@@ -764,10 +774,11 @@ static int set_ep_max_packet_size_bint(struct device *dev, const struct f_uac2_o
 	return 0;
 }
 
-static struct uac2_feature_unit_descriptor *build_fu_desc(int chmask)
+static struct uac2_feature_unit_descriptor *build_fu_desc(bool is_playback,
+							  const struct f_uac2_opts *opts)
 {
 	struct uac2_feature_unit_descriptor *fu_desc;
-	int channels = num_channels(chmask);
+	unsigned int channels = uac2_num_channels(is_playback, opts);
 	int fu_desc_size = UAC2_DT_FEATURE_UNIT_SIZE(channels);
 
 	fu_desc = kzalloc(fu_desc_size, GFP_KERNEL);
@@ -976,13 +987,27 @@ static int afunc_validate_opts(struct g_audio *agdev, struct device *dev)
 {
 	struct f_uac2_opts *opts = g_audio_to_uac2_opts(agdev);
 	const char *msg = NULL;
+	unsigned int p_channels = uac2_num_channels(true, opts);
+	unsigned int c_channels = uac2_num_channels(false, opts);
 
-	if (!opts->p_chmask && !opts->c_chmask)
-		msg = "no playback and capture channels";
-	else if (opts->p_chmask & ~UAC2_CHANNEL_MASK)
+	if (opts->p_chmask & ~UAC2_CHANNEL_MASK)
 		msg = "unsupported playback channels mask";
 	else if (opts->c_chmask & ~UAC2_CHANNEL_MASK)
 		msg = "unsupported capture channels mask";
+	else if (!p_channels && !c_channels)
+		msg = "no playback and capture channels";
+	else if (opts->p_channels && opts->p_chmask &&
+		 opts->p_channels != num_channels(opts->p_chmask))
+		msg = "playback channel count does not match channel mask";
+	else if (opts->c_channels && opts->c_chmask &&
+		 opts->c_channels != num_channels(opts->c_chmask))
+		msg = "capture channel count does not match channel mask";
+	else if (FUIN_EN(opts) &&
+		 UAC2_DT_FEATURE_UNIT_SIZE(p_channels) > U8_MAX)
+		msg = "too many playback channels for feature unit descriptor";
+	else if (FUOUT_EN(opts) &&
+		 UAC2_DT_FEATURE_UNIT_SIZE(c_channels) > U8_MAX)
+		msg = "too many capture channels for feature unit descriptor";
 	else if ((opts->p_ssize < 1) || (opts->p_ssize > 4))
 		msg = "incorrect playback sample size";
 	else if ((opts->c_ssize < 1) || (opts->c_ssize > 4))
@@ -1059,12 +1084,12 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 		return PTR_ERR(us);
 
 	if (FUOUT_EN(uac2_opts)) {
-		out_feature_unit_desc = build_fu_desc(uac2_opts->c_chmask);
+		out_feature_unit_desc = build_fu_desc(false, uac2_opts);
 		if (!out_feature_unit_desc)
 			return -ENOMEM;
 	}
 	if (FUIN_EN(uac2_opts)) {
-		in_feature_unit_desc = build_fu_desc(uac2_opts->p_chmask);
+		in_feature_unit_desc = build_fu_desc(true, uac2_opts);
 		if (!in_feature_unit_desc) {
 			ret = -ENOMEM;
 			goto err_free_fu;
@@ -1099,13 +1124,13 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 
 
 	/* Initialize the configurable parameters */
-	usb_out_it_desc.bNrChannels = num_channels(uac2_opts->c_chmask);
+	usb_out_it_desc.bNrChannels = uac2_num_channels(false, uac2_opts);
 	usb_out_it_desc.bmChannelConfig = cpu_to_le32(uac2_opts->c_chmask);
-	io_in_it_desc.bNrChannels = num_channels(uac2_opts->p_chmask);
+	io_in_it_desc.bNrChannels = uac2_num_channels(true, uac2_opts);
 	io_in_it_desc.bmChannelConfig = cpu_to_le32(uac2_opts->p_chmask);
-	as_out_hdr_desc.bNrChannels = num_channels(uac2_opts->c_chmask);
+	as_out_hdr_desc.bNrChannels = uac2_num_channels(false, uac2_opts);
 	as_out_hdr_desc.bmChannelConfig = cpu_to_le32(uac2_opts->c_chmask);
-	as_in_hdr_desc.bNrChannels = num_channels(uac2_opts->p_chmask);
+	as_in_hdr_desc.bNrChannels = uac2_num_channels(true, uac2_opts);
 	as_in_hdr_desc.bmChannelConfig = cpu_to_le32(uac2_opts->p_chmask);
 	as_out_fmt1_desc.bSubslotSize = uac2_opts->c_ssize;
 	as_out_fmt1_desc.bBitResolution = uac2_opts->c_ssize * 8;
@@ -1308,7 +1333,7 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 	agdev->gadget = gadget;
 
 	agdev->params.p_chmask = uac2_opts->p_chmask;
-	agdev->params.p_channels = num_channels(uac2_opts->p_chmask);
+	agdev->params.p_channels = uac2_num_channels(true, uac2_opts);
 	memcpy(agdev->params.p_srates, uac2_opts->p_srates,
 			sizeof(agdev->params.p_srates));
 	agdev->params.p_ssize = uac2_opts->p_ssize;
@@ -1321,7 +1346,7 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 		agdev->params.p_fu.volume_res = uac2_opts->p_volume_res;
 	}
 	agdev->params.c_chmask = uac2_opts->c_chmask;
-	agdev->params.c_channels = num_channels(uac2_opts->c_chmask);
+	agdev->params.c_channels = uac2_num_channels(false, uac2_opts);
 	memcpy(agdev->params.c_srates, uac2_opts->c_srates,
 			sizeof(agdev->params.c_srates));
 	agdev->params.c_ssize = uac2_opts->c_ssize;
@@ -2086,10 +2111,12 @@ end:									\
 CONFIGFS_ATTR(f_uac2_opts_, name)
 
 UAC2_ATTRIBUTE(u32, p_chmask);
+UAC2_ATTRIBUTE(u8, p_channels);
 UAC2_RATE_ATTRIBUTE(p_srate);
 UAC2_ATTRIBUTE(u32, p_ssize);
 UAC2_ATTRIBUTE(u8, p_hs_bint);
 UAC2_ATTRIBUTE(u32, c_chmask);
+UAC2_ATTRIBUTE(u8, c_channels);
 UAC2_RATE_ATTRIBUTE(c_srate);
 UAC2_ATTRIBUTE_SYNC(c_sync);
 UAC2_ATTRIBUTE(u32, c_ssize);
@@ -2129,10 +2156,12 @@ UAC2_ATTRIBUTE(s16, c_terminal_type);
 
 static struct configfs_attribute *f_uac2_attrs[] = {
 	&f_uac2_opts_attr_p_chmask,
+	&f_uac2_opts_attr_p_channels,
 	&f_uac2_opts_attr_p_srate,
 	&f_uac2_opts_attr_p_ssize,
 	&f_uac2_opts_attr_p_hs_bint,
 	&f_uac2_opts_attr_c_chmask,
+	&f_uac2_opts_attr_c_channels,
 	&f_uac2_opts_attr_c_srate,
 	&f_uac2_opts_attr_c_ssize,
 	&f_uac2_opts_attr_c_hs_bint,
@@ -2202,10 +2231,12 @@ static struct usb_function_instance *afunc_alloc_inst(void)
 				    &f_uac2_func_type);
 
 	opts->p_chmask = UAC2_DEF_PCHMASK;
+	opts->p_channels = UAC2_DEF_PCHANNELS;
 	opts->p_srates[0] = UAC2_DEF_PSRATE;
 	opts->p_ssize = UAC2_DEF_PSSIZE;
 	opts->p_hs_bint = UAC2_DEF_PHSBINT;
 	opts->c_chmask = UAC2_DEF_CCHMASK;
+	opts->c_channels = UAC2_DEF_CCHANNELS;
 	opts->c_srates[0] = UAC2_DEF_CSRATE;
 	opts->c_ssize = UAC2_DEF_CSSIZE;
 	opts->c_hs_bint = UAC2_DEF_CHSBINT;
diff --git a/drivers/usb/gadget/function/u_uac2.h b/drivers/usb/gadget/function/u_uac2.h
index 0df808289ded..bacd841c9df6 100644
--- a/drivers/usb/gadget/function/u_uac2.h
+++ b/drivers/usb/gadget/function/u_uac2.h
@@ -17,10 +17,12 @@
 #include "uac_common.h"
 
 #define UAC2_DEF_PCHMASK 0x3
+#define UAC2_DEF_PCHANNELS 0  /* 0 = derive from p_chmask */
 #define UAC2_DEF_PSRATE 48000
 #define UAC2_DEF_PSSIZE 2
 #define UAC2_DEF_PHSBINT 0
 #define UAC2_DEF_CCHMASK 0x3
+#define UAC2_DEF_CCHANNELS 0  /* 0 = derive from c_chmask */
 #define UAC2_DEF_CSRATE 64000
 #define UAC2_DEF_CSSIZE 2
 #define UAC2_DEF_CHSBINT 0
@@ -46,11 +48,13 @@ struct f_uac2_opts {
 	int				p_srates[UAC_MAX_RATES];
 	int				p_ssize;
 	u8				p_hs_bint;
+	u8				p_channels;
 	int				c_chmask;
 	int				c_srates[UAC_MAX_RATES];
 	int				c_ssize;
 	int				c_sync;
 	u8				c_hs_bint;
+	u8				c_channels;
 
 	bool			p_mute_present;
 	bool			p_volume_present;
-- 
2.34.1