dmaengine: idxd: Expose DSA3.0 capabilities through sysfs

Introduce sysfs interfaces for 3 new Data Streaming Accelerator (DSA)
capability registers (dsacap0-2) to enable userspace awareness of hardware
features in DSA version 3 and later devices.

Userspace components (e.g. configure libraries, workload Apps) require this
information to:
1. Select optimal data transfer strategies based on SGL capabilities
2. Enable hardware-specific optimizations for floating-point operations
3. Configure memory operations with proper numerical handling
4. Verify compute operation compatibility before submitting jobs

The output format is <dsacap2>,<dsacap1>,<dsacap0>, where each DSA
capability value is a 64-bit hexadecimal number, separated by commas.
The ordering follows the DSA 3.0 specification layout:
 Offset:    0x190    0x188    0x180
 Reg:       dsacap2  dsacap1  dsacap0

Example:
cat /sys/bus/dsa/devices/dsa0/dsacaps
 000000000000f18d,0014000e000007aa,00fa01ff01ff03ff

According to the DSA 3.0 specification, there are 15 fields defined for
the three dsacap registers. However, there's no need to define all
register structures unless a use case requires them. At this point,
support for the Scatter-Gather List (SGL) located in dsacap0 is necessary,
so only dsacap0 is defined accordingly.

For reference, the DSA 3.0 specification is available at:
Link: https://software.intel.com/content/www/us/en/develop/articles/intel-data-streaming-accelerator-architecture-specification.html

Signed-off-by: Yi Sun <yi.sun@intel.com>
Co-developed-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Link: https://patch.msgid.link/20260107-idxd-yi-sun-dsa3-sgl-size-v2-1-dbef8f559e48@intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/ABI/stable/sysfs-driver-dma-idxd

@@ -136,6 +136,21 @@ Description:	The last executed device administrative command's status/error.
 		Also last configuration error overloaded.
 		Writing to it will clear the status.
 
+What:		/sys/bus/dsa/devices/dsa<m>/dsacaps
+Date:		April 5, 2026
+KernelVersion:	6.20.0
+Contact:	dmaengine@vger.kernel.org
+Description:	The DSA3 specification introduces three new capability
+		registers: dsacap[0-2]. User components (e.g., configuration
+		libraries and workload applications) require this information
+		to properly utilize the DSA3 features.
+		This includes SGL capability support, Enabling hardware-specific
+		optimizations, Configuring memory, etc.
+		The output format is '<dsacap2>,<dsacap1>,<dsacap0>' where each
+		DSA cap value is a 64 bit hex value.
+		This attribute should only be visible on DSA devices of version
+		3 or later.
+
 What:		/sys/bus/dsa/devices/dsa<m>/iaa_cap
 Date:		Sept 14, 2022
 KernelVersion: 6.0.0

drivers/dma/idxd/idxd.h

@@ -252,6 +252,9 @@ struct idxd_hw {
 	struct opcap opcap;
 	u32 cmd_cap;
 	union iaa_cap_reg iaa_cap;
+	union dsacap0_reg dsacap0;
+	union dsacap1_reg dsacap1;
+	union dsacap2_reg dsacap2;
 };
 
 enum idxd_device_state {

drivers/dma/idxd/init.c

@@ -585,6 +585,12 @@ static void idxd_read_caps(struct idxd_device *idxd)
 	}
 	multi_u64_to_bmap(idxd->opcap_bmap, &idxd->hw.opcap.bits[0], 4);
 
+	if (idxd->hw.version >= DEVICE_VERSION_3) {
+		idxd->hw.dsacap0.bits = ioread64(idxd->reg_base + IDXD_DSACAP0_OFFSET);
+		idxd->hw.dsacap1.bits = ioread64(idxd->reg_base + IDXD_DSACAP1_OFFSET);
+		idxd->hw.dsacap2.bits = ioread64(idxd->reg_base + IDXD_DSACAP2_OFFSET);
+	}
+
 	/* read iaa cap */
 	if (idxd->data->type == IDXD_TYPE_IAX && idxd->hw.version >= DEVICE_VERSION_2)
 		idxd->hw.iaa_cap.bits = ioread64(idxd->reg_base + IDXD_IAACAP_OFFSET);

drivers/dma/idxd/registers.h

@@ -18,6 +18,7 @@
 
 #define DEVICE_VERSION_1		0x100
 #define DEVICE_VERSION_2		0x200
+#define DEVICE_VERSION_3		0x300
 
 #define IDXD_MMIO_BAR		0
 #define IDXD_WQ_BAR		2
@@ -587,6 +588,30 @@ union evl_status_reg {
 	u64 bits;
 };
 
+#define IDXD_DSACAP0_OFFSET		0x180
+union dsacap0_reg {
+	u64 bits;
+	struct {
+		u64 max_sgl_shift:4;
+		u64 max_gr_block_shift:4;
+		u64 ops_inter_domain:7;
+		u64 rsvd1:17;
+		u64 sgl_formats:16;
+		u64 max_sg_process:8;
+		u64 rsvd2:8;
+	};
+};
+
+#define IDXD_DSACAP1_OFFSET		0x188
+union dsacap1_reg {
+	u64 bits;
+};
+
+#define IDXD_DSACAP2_OFFSET		0x190
+union dsacap2_reg {
+	u64 bits;
+};
+
 #define IDXD_MAX_BATCH_IDENT	256
 
 struct __evl_entry {

drivers/dma/idxd/sysfs.c

@@ -1713,6 +1713,18 @@ static ssize_t event_log_size_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(event_log_size);
 
+static ssize_t dsacaps_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct idxd_device *idxd = confdev_to_idxd(dev);
+
+	return sysfs_emit(buf, "%016llx,%016llx,%016llx\n",
+			  (u64)idxd->hw.dsacap2.bits,
+			  (u64)idxd->hw.dsacap1.bits,
+			  (u64)idxd->hw.dsacap0.bits);
+}
+static DEVICE_ATTR_RO(dsacaps);
+
 static bool idxd_device_attr_max_batch_size_invisible(struct attribute *attr,
 						      struct idxd_device *idxd)
 {
@@ -1750,6 +1762,14 @@ static bool idxd_device_attr_event_log_size_invisible(struct attribute *attr,
 		!idxd->hw.gen_cap.evl_support);
 }
 
+static bool idxd_device_attr_dsacaps_invisible(struct attribute *attr,
+					       struct idxd_device *idxd)
+{
+	return attr == &dev_attr_dsacaps.attr &&
+		(idxd->data->type != IDXD_TYPE_DSA ||
+		idxd->hw.version < DEVICE_VERSION_3);
+}
+
 static umode_t idxd_device_attr_visible(struct kobject *kobj,
 					struct attribute *attr, int n)
 {
@@ -1768,6 +1788,9 @@ static umode_t idxd_device_attr_visible(struct kobject *kobj,
 	if (idxd_device_attr_event_log_size_invisible(attr, idxd))
 		return 0;
 
+	if (idxd_device_attr_dsacaps_invisible(attr, idxd))
+		return 0;
+
 	return attr->mode;
 }
 
@@ -1795,6 +1818,7 @@ static struct attribute *idxd_device_attributes[] = {
 	&dev_attr_cmd_status.attr,
 	&dev_attr_iaa_cap.attr,
 	&dev_attr_event_log_size.attr,
+	&dev_attr_dsacaps.attr,
 	NULL,
 };