drm: document drm_ioctl.[hc]

Also unify/merge with the existing stuff.

I was a bit torn where to put this, but in the end I decided to put
all the ioctl/sysfs/debugfs stuff into drm-uapi.rst. That means we
have a bit a split with the other uapi related stuff used internally,
like drm_file.[hc], but I think overall this makes more sense.

If it's too confusing we can always add more cross-links to make it
more discoverable. But the auto-sprinkling of links kernel-doc already
does seems sufficient.

Also for prettier docs and more cross-links, switch the internal
defines over to an enum, as usual.

v2: Update kerneldoc fro drm_compat_ioctl too (caught by 0day), plus a
bit more drive-by polish.

v3: Fix typo, spotted by xerpi on irc (Sergi).

v4: Add missing space in comment (Neil).

Cc: Sergi Granell <xerpi.g.12@gmail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170404095304.17599-4-daniel.vetter@ffwll.ch

2 files changed, 88 insertions, 38 deletions

diff --git a/drivers/gpu/drm/drm_ioc32.c b/drivers/gpu/drm/drm_ioc32.c
index b134482f4022..ae386783e3ea 100644
--- a/drivers/gpu/drm/drm_ioc32.c
+++ b/drivers/gpu/drm/drm_ioc32.c
@@ -1,4 +1,4 @@
-/**
+/*
  * \file drm_ioc32.c
  *
  * 32-bit ioctl compatibility routines for the DRM.
@@ -72,15 +72,15 @@
 #define DRM_IOCTL_MODE_ADDFB232		DRM_IOWR(0xb8, drm_mode_fb_cmd232_t)
 
 typedef struct drm_version_32 {
-	int version_major;	  /**< Major version */
-	int version_minor;	  /**< Minor version */
-	int version_patchlevel;	   /**< Patch level */
-	u32 name_len;		  /**< Length of name buffer */
-	u32 name;		  /**< Name of driver */
-	u32 date_len;		  /**< Length of date buffer */
-	u32 date;		  /**< User-space buffer to hold date */
-	u32 desc_len;		  /**< Length of desc buffer */
-	u32 desc;		  /**< User-space buffer to hold desc */
+	int version_major;	  /* Major version */
+	int version_minor;	  /* Minor version */
+	int version_patchlevel;	   /* Patch level */
+	u32 name_len;		  /* Length of name buffer */
+	u32 name;		  /* Name of driver */
+	u32 date_len;		  /* Length of date buffer */
+	u32 date;		  /* User-space buffer to hold date */
+	u32 desc_len;		  /* Length of desc buffer */
+	u32 desc;		  /* User-space buffer to hold desc */
 } drm_version32_t;
 
 static int compat_drm_version(struct file *file, unsigned int cmd,
@@ -126,8 +126,8 @@ static int compat_drm_version(struct file *file, unsigned int cmd,
 }
 
 typedef struct drm_unique32 {
-	u32 unique_len;	/**< Length of unique */
-	u32 unique;	/**< Unique name for driver instantiation */
+	u32 unique_len;	/* Length of unique */
+	u32 unique;	/* Unique name for driver instantiation */
 } drm_unique32_t;
 
 static int compat_drm_getunique(struct file *file, unsigned int cmd,
@@ -180,12 +180,12 @@ static int compat_drm_setunique(struct file *file, unsigned int cmd,
 }
 
 typedef struct drm_map32 {
-	u32 offset;		/**< Requested physical address (0 for SAREA)*/
-	u32 size;		/**< Requested physical size (bytes) */
-	enum drm_map_type type;	/**< Type of memory to map */
-	enum drm_map_flags flags;	/**< Flags */
-	u32 handle;		/**< User-space: "Handle" to pass to mmap() */
-	int mtrr;		/**< MTRR slot used */
+	u32 offset;		/* Requested physical address (0 for SAREA) */
+	u32 size;		/* Requested physical size (bytes) */
+	enum drm_map_type type;	/* Type of memory to map */
+	enum drm_map_flags flags;	/* Flags */
+	u32 handle;		/* User-space: "Handle" to pass to mmap() */
+	int mtrr;		/* MTRR slot used */
 } drm_map32_t;
 
 static int compat_drm_getmap(struct file *file, unsigned int cmd,
@@ -286,12 +286,12 @@ static int compat_drm_rmmap(struct file *file, unsigned int cmd,
 }
 
 typedef struct drm_client32 {
-	int idx;	/**< Which client desired? */
-	int auth;	/**< Is client authenticated? */
-	u32 pid;	/**< Process ID */
-	u32 uid;	/**< User ID */
-	u32 magic;	/**< Magic */
-	u32 iocs;	/**< Ioctl count */
+	int idx;	/* Which client desired? */
+	int auth;	/* Is client authenticated? */
+	u32 pid;	/* Process ID */
+	u32 uid;	/* User ID */
+	u32 magic;	/* Magic */
+	u32 iocs;	/* Ioctl count */
 } drm_client32_t;
 
 static int compat_drm_getclient(struct file *file, unsigned int cmd,
@@ -366,12 +366,12 @@ static int compat_drm_getstats(struct file *file, unsigned int cmd,
 }
 
 typedef struct drm_buf_desc32 {
-	int count;		 /**< Number of buffers of this size */
-	int size;		 /**< Size in bytes */
-	int low_mark;		 /**< Low water mark */
-	int high_mark;		 /**< High water mark */
+	int count;		 /* Number of buffers of this size */
+	int size;		 /* Size in bytes */
+	int low_mark;		 /* Low water mark */
+	int high_mark;		 /* High water mark */
 	int flags;
-	u32 agp_start;		 /**< Start address in the AGP aperture */
+	u32 agp_start;		 /* Start address in the AGP aperture */
 } drm_buf_desc32_t;
 
 static int compat_drm_addbufs(struct file *file, unsigned int cmd,
@@ -1111,13 +1111,18 @@ static drm_ioctl_compat_t *drm_compat_ioctls[] = {
 };
 
 /**
- * Called whenever a 32-bit process running under a 64-bit kernel
- * performs an ioctl on /dev/drm.
+ * drm_compat_ioctl - 32bit IOCTL compatibility handler for DRM drivers
+ * @filp: file this ioctl is called on
+ * @cmd: ioctl cmd number
+ * @arg: user argument
+ *
+ * Compatibility handler for 32 bit userspace running on 64 kernels. All actual
+ * IOCTL handling is forwarded to drm_ioctl(), while marshalling structures as
+ * appropriate. Note that this only handles DRM core IOCTLs, if the driver has
+ * botched IOCTL itself, it must handle those by wrapping this function.
  *
- * \param file_priv DRM file private.
- * \param cmd command.
- * \param arg user argument.
- * \return zero on success or negative number on failure.
+ * Returns:
+ * Zero on success, negative error code on failure.
  */
 long drm_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
@@ -1141,5 +1146,4 @@ long drm_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 	return ret;
 }
-
 EXPORT_SYMBOL(drm_compat_ioctl);
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 7d6deaa91281..9f4241f0dd9c 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -647,13 +647,59 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
 #define DRM_CORE_IOCTL_COUNT	ARRAY_SIZE( drm_ioctls )
 
 /**
+ * DOC: driver specific ioctls
+ *
+ * First things first, driver private IOCTLs should only be needed for drivers
+ * supporting rendering. Kernel modesetting is all standardized, and extended
+ * through properties. There are a few exceptions in some existing drivers,
+ * which define IOCTL for use by the display DRM master, but they all predate
+ * properties.
+ *
+ * Now if you do have a render driver you always have to support it through
+ * driver private properties. There's a few steps needed to wire all the things
+ * up.
+ *
+ * First you need to define the structure for your IOCTL in your driver private
+ * UAPI header in ``include/uapi/drm/my_driver_drm.h``::
+ *
+ *     struct my_driver_operation {
+ *             u32 some_thing;
+ *             u32 another_thing;
+ *     };
+ *
+ * Please make sure that you follow all the best practices from
+ * ``Documentation/ioctl/botching-up-ioctls.txt``. Note that drm_ioctl()
+ * automatically zero-extends structures, hence make sure you can add more stuff
+ * at the end, i.e. don't put a variable sized array there.
+ *
+ * Then you need to define your IOCTL number, using one of DRM_IO(), DRM_IOR(),
+ * DRM_IOW() or DRM_IOWR(). It must start with the DRM_IOCTL\_ prefix::
+ *
+ *     ##define DRM_IOCTL_MY_DRIVER_OPERATION \
+ *         DRM_IOW(DRM_COMMAND_BASE, struct my_driver_operation)
+ * 
+ * DRM driver private IOCTL must be in the range from DRM_COMMAND_BASE to
+ * DRM_COMMAND_END. Finally you need an array of &struct drm_ioctl_desc to wire
+ * up the handlers and set the access rights:
+ *
+ *     static const struct drm_ioctl_desc my_driver_ioctls[] = {
+ *         DRM_IOCTL_DEF_DRV(MY_DRIVER_OPERATION, my_driver_operation,
+ *                 DRM_AUTH|DRM_RENDER_ALLOW),
+ *     };
+ *
+ * And then assign this to the &drm_driver.ioctls field in your driver
+ * structure.
+ */
+
+/**
  * drm_ioctl - ioctl callback implementation for DRM drivers
  * @filp: file this ioctl is called on
  * @cmd: ioctl cmd number
  * @arg: user argument
  *
- * Looks up the ioctl function in the ::ioctls table, checking for root
- * previleges if so required, and dispatches to the respective function.
+ * Looks up the ioctl function in the DRM core and the driver dispatch table,
+ * stored in &drm_driver.ioctls. It checks for necessary permission by calling
+ * drm_ioctl_permit(), and dispatches to the respective function.
  *
  * Returns:
  * Zero on success, negative error code on failure.