tools/testing/cxl: Add a sysfs attr to test poison inject limits

CXL devices may report a maximum number of addresses that a device
allows to be poisoned using poison injection. When cxl_test creates
mock CXL memory devices, it defaults to MOCK_INJECT_DEV_MAX==88 for
all mocked memdevs.

Add a sysfs attribute, poison_inject_max to module cxl_mock_mem so
that users can set a custom device injection limit. Fail, and return
-EBUSY, if the mock poison list is not empty.

/sys/bus/platform/drivers/cxl_mock_mem/poison_inject_max

A simple usage model is to set the attribute before running a test in
order to emulate a device's poison handling.
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/0f25b2862b90013545450222d2199e435c6cc11a.1681874357.git.alison.schofield@intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

tools/testing/cxl/test/mem.c

@@ -19,6 +19,8 @@
 #define MOCK_INJECT_DEV_MAX 8
 #define MOCK_INJECT_TEST_MAX 128
 
+static unsigned int poison_inject_dev_max = MOCK_INJECT_DEV_MAX;
+
 static struct cxl_cel_entry mock_cel[] = {
 	{
 		.opcode = cpu_to_le16(CXL_MBOX_OP_GET_SUPPORTED_LOGS),
@@ -485,7 +487,7 @@ static int mock_id(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd)
 			cpu_to_le64(SZ_256M / CXL_CAPACITY_MULTIPLIER),
 		.total_capacity =
 			cpu_to_le64(DEV_SIZE / CXL_CAPACITY_MULTIPLIER),
-		.inject_poison_limit = cpu_to_le16(MOCK_INJECT_DEV_MAX),
+		.inject_poison_limit = cpu_to_le16(MOCK_INJECT_TEST_MAX),
 	};
 
 	put_unaligned_le24(CXL_POISON_LIST_MAX, id.poison_list_max_mer);
@@ -919,7 +921,7 @@ cxl_get_injected_po(struct cxl_dev_state *cxlds, u64 offset, u64 length)
 	int nr_records = 0;
 	u64 dpa;
 
-	po = kzalloc(struct_size(po, record, MOCK_INJECT_DEV_MAX), GFP_KERNEL);
+	po = kzalloc(struct_size(po, record, poison_inject_dev_max), GFP_KERNEL);
 	if (!po)
 		return NULL;
 
@@ -934,7 +936,7 @@ cxl_get_injected_po(struct cxl_dev_state *cxlds, u64 offset, u64 length)
 		po->record[nr_records].address = cpu_to_le64(dpa);
 		po->record[nr_records].length = cpu_to_le32(1);
 		nr_records++;
-		if (nr_records == MOCK_INJECT_DEV_MAX)
+		if (nr_records == poison_inject_dev_max)
 			break;
 	}
 
@@ -972,7 +974,7 @@ static bool mock_poison_dev_max_injected(struct cxl_dev_state *cxlds)
 		if (mock_poison_list[i].cxlds == cxlds)
 			count++;
 	}
-	return (count >= MOCK_INJECT_DEV_MAX);
+	return (count >= poison_inject_dev_max);
 }
 
 static bool mock_poison_add(struct cxl_dev_state *cxlds, u64 dpa)
@@ -1054,6 +1056,47 @@ static int mock_clear_poison(struct cxl_dev_state *cxlds,
 	return 0;
 }
 
+static bool mock_poison_list_empty(void)
+{
+	for (int i = 0; i < MOCK_INJECT_TEST_MAX; i++) {
+		if (mock_poison_list[i].cxlds)
+			return false;
+	}
+	return true;
+}
+
+static ssize_t poison_inject_max_show(struct device_driver *drv, char *buf)
+{
+	return sysfs_emit(buf, "%u\n", poison_inject_dev_max);
+}
+
+static ssize_t poison_inject_max_store(struct device_driver *drv,
+				       const char *buf, size_t len)
+{
+	int val;
+
+	if (kstrtoint(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (!mock_poison_list_empty())
+		return -EBUSY;
+
+	if (val <= MOCK_INJECT_TEST_MAX)
+		poison_inject_dev_max = val;
+	else
+		return -EINVAL;
+
+	return len;
+}
+
+static DRIVER_ATTR_RW(poison_inject_max);
+
+static struct attribute *cxl_mock_mem_core_attrs[] = {
+	&driver_attr_poison_inject_max.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(cxl_mock_mem_core);
+
 static int cxl_mock_mbox_send(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd)
 {
 	struct device *dev = cxlds->dev;
@@ -1262,6 +1305,7 @@ static struct platform_driver cxl_mock_mem_driver = {
 	.driver = {
 		.name = KBUILD_MODNAME,
 		.dev_groups = cxl_mock_mem_groups,
+		.groups = cxl_mock_mem_core_groups,
 	},
 };