crypto/nx: Add sysfs interface to export NX capabilities

Export NX-GZIP capabilities to usrespace in sysfs
/sys/devices/vio/ibm,compression-v1/nx_gzip_caps directory.
These are queried by userspace accelerator libraries to set
minimum length heuristics and maximum limits on request sizes.

NX-GZIP capabilities:
min_compress_len  /*Recommended minimum compress length in bytes*/
min_decompress_len /*Recommended minimum decompress length in bytes*/
req_max_processed_len /* Maximum number of bytes processed in one
			request */

NX will return RMA_Reject if the request buffer size is greater
than req_max_processed_len.
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/510da86abbd904878d5f13d74aba72603c37d783.camel@linux.ibm.com

drivers/crypto/nx/nx-common-pseries.c

@@ -967,6 +967,36 @@ static struct attribute_group nx842_attribute_group = {
 	.attrs = nx842_sysfs_entries,
 };
 
+#define	nxcop_caps_read(_name)						\
+static ssize_t nxcop_##_name##_show(struct device *dev,			\
+			struct device_attribute *attr, char *buf)	\
+{									\
+	return sprintf(buf, "%lld\n", nx_cop_caps._name);		\
+}
+
+#define NXCT_ATTR_RO(_name)						\
+	nxcop_caps_read(_name);						\
+	static struct device_attribute dev_attr_##_name = __ATTR(_name,	\
+						0444,			\
+						nxcop_##_name##_show,	\
+						NULL);
+
+NXCT_ATTR_RO(req_max_processed_len);
+NXCT_ATTR_RO(min_compress_len);
+NXCT_ATTR_RO(min_decompress_len);
+
+static struct attribute *nxcop_caps_sysfs_entries[] = {
+	&dev_attr_req_max_processed_len.attr,
+	&dev_attr_min_compress_len.attr,
+	&dev_attr_min_decompress_len.attr,
+	NULL,
+};
+
+static struct attribute_group nxcop_caps_attr_group = {
+	.name	=	"nx_gzip_caps",
+	.attrs	=	nxcop_caps_sysfs_entries,
+};
+
 static struct nx842_driver nx842_pseries_driver = {
 	.name =		KBUILD_MODNAME,
 	.owner =	THIS_MODULE,
@@ -1056,6 +1086,16 @@ static int nx842_probe(struct vio_dev *viodev,
 		goto error;
 	}
 
+	if (caps_feat) {
+		if (sysfs_create_group(&viodev->dev.kobj,
+					&nxcop_caps_attr_group)) {
+			dev_err(&viodev->dev,
+				"Could not create sysfs NX capability entries\n");
+			ret = -1;
+			goto error;
+		}
+	}
+
 	return 0;
 
 error_unlock:
@@ -1075,6 +1115,9 @@ static void nx842_remove(struct vio_dev *viodev)
 	pr_info("Removing IBM Power 842 compression device\n");
 	sysfs_remove_group(&viodev->dev.kobj, &nx842_attribute_group);
 
+	if (caps_feat)
+		sysfs_remove_group(&viodev->dev.kobj, &nxcop_caps_attr_group);
+
 	crypto_unregister_alg(&nx842_pseries_alg);
 
 	spin_lock_irqsave(&devdata_mutex, flags);