drm/xe/configfs: Add post context restore bb

Allow the user to specify commands to execute during a context restore.
Currently it's possible to parse 2 types of actions:

	- cmd: the instructions are added as is to the bb
	- reg: just use the address and value, without worrying about
	  encoding the right LRI instruction. This is possibly the most
	  useful use case, so added a dedicated action for that.

This also prepares for future BBs: mid context restore and rc6 context
restore that can re-use the same parsing functions.

Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Link: https://lore.kernel.org/r/20250916-wa-bb-cmds-v5-4-306bddbc15da@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

drivers/gpu/drm/xe/xe_configfs.c

@@ -4,6 +4,7 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/ctype.h>
 #include <linux/configfs.h>
 #include <linux/cleanup.h>
 #include <linux/find.h>
@@ -12,6 +13,7 @@
 #include <linux/pci.h>
 #include <linux/string.h>
 
+#include "instructions/xe_mi_commands.h"
 #include "xe_configfs.h"
 #include "xe_hw_engine_types.h"
 #include "xe_module.h"
@@ -115,6 +117,37 @@
  *
  * This attribute can only be set before binding to the device.
  *
+ * Context restore BB
+ * ------------------
+ *
+ * Allow to execute a batch buffer during any context switches. When the
+ * GPU is restoring the context, it executes additional commands. It's useful
+ * for testing additional workarounds and validating certain HW behaviors: it's
+ * not intended for normal execution and will taint the kernel with TAINT_TEST
+ * when used.
+ *
+ * Currently this is implemented only for post context restore. Examples:
+ *
+ * #. Execute a LRI command to write 0xDEADBEEF to register 0x4f10::
+ *
+ *	# echo 'rcs cmd 11000001 4F100 DEADBEEF' \
+ *		> /sys/kernel/config/xe/0000:03:00.0/ctx_restore_post_bb
+ *
+ * #. Load certain values in a couple of registers (it can be used as a simpler
+ *    alternative to the `cmd`) action::
+ *
+ *	# cat > /sys/kernel/config/xe/0000:03:00.0/ctx_restore_post_bb <<EOF
+ *	rcs reg 4F100 DEADBEEF
+ *	rcs reg 4F104 FFFFFFFF
+ *	EOF
+ *
+ *    .. note::
+ *
+ *       When using multiple lines, make sure to use a command that is
+ *       implemented with a single write syscall, like HEREDOC.
+ *
+ * This attribute can only be set before binding to the device.
+ *
  * Remove devices
  * ==============
  *
@@ -123,11 +156,18 @@
  *	# rmdir /sys/kernel/config/xe/0000:03:00.0/
  */
 
+/* Similar to struct xe_bb, but not tied to HW (yet) */
+struct wa_bb {
+	u32 *cs;
+	u32 len; /* in dwords */
+};
+
 struct xe_config_group_device {
 	struct config_group group;
 
 	struct xe_config_device {
 		u64 engines_allowed;
+		struct wa_bb ctx_restore_post_bb[XE_ENGINE_CLASS_MAX];
 		bool survivability_mode;
 		bool enable_psmi;
 	} config;
@@ -371,11 +411,233 @@ static ssize_t enable_psmi_store(struct config_item *item, const char *page, siz
 	return len;
 }
 
+static bool wa_bb_read_advance(bool dereference, char **p,
+			       const char *append, size_t len,
+			       size_t *max_size)
+{
+	if (dereference) {
+		if (len >= *max_size)
+			return false;
+		*max_size -= len;
+		if (append)
+			memcpy(*p, append, len);
+	}
+
+	*p += len;
+
+	return true;
+}
+
+static ssize_t wa_bb_show(struct xe_config_group_device *dev,
+			  struct wa_bb wa_bb[static XE_ENGINE_CLASS_MAX],
+			  char *data, size_t sz)
+{
+	char *p = data;
+
+	guard(mutex)(&dev->lock);
+
+	for (size_t i = 0; i < ARRAY_SIZE(engine_info); i++) {
+		enum xe_engine_class ec = engine_info[i].engine_class;
+		size_t len;
+
+		if (!wa_bb[ec].len)
+			continue;
+
+		len = snprintf(p, sz, "%s:", engine_info[i].cls);
+		if (!wa_bb_read_advance(data, &p, NULL, len, &sz))
+			return -ENOBUFS;
+
+		for (size_t j = 0; j < wa_bb[ec].len; j++) {
+			len = snprintf(p, sz, " %08x", wa_bb[ec].cs[j]);
+			if (!wa_bb_read_advance(data, &p, NULL, len, &sz))
+				return -ENOBUFS;
+		}
+
+		if (!wa_bb_read_advance(data, &p, "\n", 1, &sz))
+			return -ENOBUFS;
+	}
+
+	if (!wa_bb_read_advance(data, &p, "", 1, &sz))
+		return -ENOBUFS;
+
+	/* Reserve one more to match check for '\0' */
+	if (!data)
+		p++;
+
+	return p - data;
+}
+
+static ssize_t ctx_restore_post_bb_show(struct config_item *item, char *page)
+{
+	struct xe_config_group_device *dev = to_xe_config_group_device(item);
+
+	return wa_bb_show(dev, dev->config.ctx_restore_post_bb, page, SZ_4K);
+}
+
+static void wa_bb_append(struct wa_bb *wa_bb, u32 val)
+{
+	if (wa_bb->cs)
+		wa_bb->cs[wa_bb->len] = val;
+
+	wa_bb->len++;
+}
+
+static ssize_t parse_hex(const char *line, u32 *pval)
+{
+	char numstr[12];
+	const char *p;
+	ssize_t numlen;
+
+	p = line + strspn(line, " \t");
+	if (!*p || *p == '\n')
+		return 0;
+
+	numlen = strcspn(p, " \t\n");
+	if (!numlen || numlen >= sizeof(numstr) - 1)
+		return -EINVAL;
+
+	memcpy(numstr, p, numlen);
+	numstr[numlen] = '\0';
+	p += numlen;
+
+	if (kstrtou32(numstr, 16, pval))
+		return -EINVAL;
+
+	return p - line;
+}
+
+/*
+ * Parse lines with the format
+ *
+ *	<engine-class> cmd <u32> <u32...>
+ *	<engine-class> reg <u32_addr> <u32_val>
+ *
+ * and optionally save them in @wa_bb[i].cs is non-NULL.
+ *
+ * Return the number of dwords parsed.
+ */
+static ssize_t parse_wa_bb_lines(const char *lines,
+				 struct wa_bb wa_bb[static XE_ENGINE_CLASS_MAX])
+{
+	ssize_t dwords = 0, ret;
+	const char *p;
+
+	for (p = lines; *p; p++) {
+		const struct engine_info *info = NULL;
+		u32 val, val2;
+
+		/* Also allow empty lines */
+		p += strspn(p, " \t\n");
+		if (!*p)
+			break;
+
+		ret = parse_engine(p, " \t\n", NULL, &info);
+		if (ret < 0)
+			return ret;
+
+		p += ret;
+		p += strspn(p, " \t");
+
+		if (str_has_prefix(p, "cmd")) {
+			for (p += strlen("cmd"); *p;) {
+				ret = parse_hex(p, &val);
+				if (ret < 0)
+					return -EINVAL;
+				if (!ret)
+					break;
+
+				p += ret;
+				dwords++;
+				wa_bb_append(&wa_bb[info->engine_class], val);
+			}
+		} else if (str_has_prefix(p, "reg")) {
+			p += strlen("reg");
+			ret = parse_hex(p, &val);
+			if (ret <= 0)
+				return -EINVAL;
+
+			p += ret;
+			ret = parse_hex(p, &val2);
+			if (ret <= 0)
+				return -EINVAL;
+
+			p += ret;
+			dwords += 3;
+			wa_bb_append(&wa_bb[info->engine_class],
+				     MI_LOAD_REGISTER_IMM | MI_LRI_NUM_REGS(1));
+			wa_bb_append(&wa_bb[info->engine_class], val);
+			wa_bb_append(&wa_bb[info->engine_class], val2);
+		} else {
+			return -EINVAL;
+		}
+	}
+
+	return dwords;
+}
+
+static ssize_t wa_bb_store(struct wa_bb wa_bb[static XE_ENGINE_CLASS_MAX],
+			   struct xe_config_group_device *dev,
+			   const char *page, size_t len)
+{
+	/* tmp_wa_bb must match wa_bb's size */
+	struct wa_bb tmp_wa_bb[XE_ENGINE_CLASS_MAX] = { };
+	ssize_t count, class;
+	u32 *tmp;
+
+	/* 1. Count dwords - wa_bb[i].cs is NULL for all classes */
+	count = parse_wa_bb_lines(page, tmp_wa_bb);
+	if (count < 0)
+		return count;
+
+	guard(mutex)(&dev->lock);
+
+	if (is_bound(dev))
+		return -EBUSY;
+
+	/*
+	 * 2. Allocate a u32 array and set the pointers to the right positions
+	 * according to the length of each class' wa_bb
+	 */
+	tmp = krealloc(wa_bb[0].cs, count * sizeof(u32), GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	if (!count) {
+		memset(wa_bb, 0, sizeof(tmp_wa_bb));
+		return len;
+	}
+
+	for (class = 0, count = 0; class < XE_ENGINE_CLASS_MAX; ++class) {
+		tmp_wa_bb[class].cs = tmp + count;
+		count += tmp_wa_bb[class].len;
+		tmp_wa_bb[class].len = 0;
+	}
+
+	/* 3. Parse wa_bb lines again, this time saving the values */
+	count = parse_wa_bb_lines(page, tmp_wa_bb);
+	if (count < 0)
+		return count;
+
+	memcpy(wa_bb, tmp_wa_bb, sizeof(tmp_wa_bb));
+
+	return len;
+}
+
+static ssize_t ctx_restore_post_bb_store(struct config_item *item,
+					 const char *data, size_t sz)
+{
+	struct xe_config_group_device *dev = to_xe_config_group_device(item);
+
+	return wa_bb_store(dev->config.ctx_restore_post_bb, dev, data, sz);
+}
+
+CONFIGFS_ATTR(, ctx_restore_post_bb);
 CONFIGFS_ATTR(, enable_psmi);
 CONFIGFS_ATTR(, engines_allowed);
 CONFIGFS_ATTR(, survivability_mode);
 
 static struct configfs_attribute *xe_config_device_attrs[] = {
+	&attr_ctx_restore_post_bb,
 	&attr_enable_psmi,
 	&attr_engines_allowed,
 	&attr_survivability_mode,
@@ -387,6 +649,8 @@ static void xe_config_device_release(struct config_item *item)
 	struct xe_config_group_device *dev = to_xe_config_group_device(item);
 
 	mutex_destroy(&dev->lock);
+
+	kfree(dev->config.ctx_restore_post_bb[0].cs);
 	kfree(dev);
 }
 
@@ -636,14 +900,26 @@ bool xe_configfs_get_psmi_enabled(struct pci_dev *pdev)
 /**
  * xe_configfs_get_ctx_restore_post_bb - get configfs ctx_restore_post_bb setting
  * @pdev: pci device
+ * @class: hw engine class
+ * @cs: pointer to the bb to use - only valid during probe
  *
- * Return: post_ctx_restore setting in configfs
+ * Return: Number of dwords used in the post_ctx_restore setting in configfs
  */
 u32 xe_configfs_get_ctx_restore_post_bb(struct pci_dev *pdev,
 					enum xe_engine_class class,
 					const u32 **cs)
 {
-	return 0;
+	struct xe_config_group_device *dev = find_xe_config_group_device(pdev);
+	u32 len;
+
+	if (!dev)
+		return 0;
+
+	*cs = dev->config.ctx_restore_post_bb[class].cs;
+	len = dev->config.ctx_restore_post_bb[class].len;
+	config_group_put(&dev->group);
+
+	return len;
 }
 
 int __init xe_configfs_init(void)