Re: [PATCH 2/3] drm: Create a format/modifier blob

[Brian Starkey <brian.starkey@arm.com>]

Hi,

Having just caught up on IRC I'm sure I'm far too late for this party,
but...

Wouldn't this whole thing be a whole lot simpler if "IN_FORMATS"
stored "pointers" to separate blobs for the format and modifier lists?

struct drm_format_modifier_blob {
#define FORMAT_BLOB_CURRENT 1
	/* Version of this blob format */
	u32 version;

	/* Flags */
	u32 flags;

	/* ID of a blob storing an array of FourCCs */
	u32 formats_blob_id;

	/* ID of a blob storing an array of drm_format_modifiers */
	u32 modifiers_blob_id;
} __packed;

I've used/written a few interfaces with offsets to
variable-length-arrays and IMO the code to handle them is always
hideous.

Added bonus: With smart enough helper code the FourCC and modifiers
blobs can be shared across planes.

-Brian

On Tue, May 02, 2017 at 10:14:27PM -0700, Ben Widawsky wrote:
>Updated blob layout (Rob, Daniel, Kristian, xerpi)
>
>Cc: Rob Clark <robdclark@gmail.com>
>Cc: Daniel Stone <daniels@collabora.com>
>Cc: Kristian H. Kristensen <hoegsberg@gmail.com>
>Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
>---
> drivers/gpu/drm/drm_mode_config.c |   7 +++
> drivers/gpu/drm/drm_plane.c       | 119 ++++++++++++++++++++++++++++++++++++++
> include/drm/drm_mode_config.h     |   6 ++
> include/uapi/drm/drm_mode.h       |  26 +++++++++
> 4 files changed, 158 insertions(+)
>
>diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
>index d9862259a2a7..6bfbc3839df5 100644
>--- a/drivers/gpu/drm/drm_mode_config.c
>+++ b/drivers/gpu/drm/drm_mode_config.c
>@@ -337,6 +337,13 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
> 		return -ENOMEM;
> 	dev->mode_config.gamma_lut_size_property = prop;
>
>+	prop = drm_property_create(dev,
>+				   DRM_MODE_PROP_IMMUTABLE | DRM_MODE_PROP_BLOB,
>+				   "IN_FORMATS", 0);
>+	if (!prop)
>+		return -ENOMEM;
>+	dev->mode_config.modifiers = prop;
>+
> 	return 0;
> }
>
>diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
>index 286e183891e5..2e89e0e73435 100644
>--- a/drivers/gpu/drm/drm_plane.c
>+++ b/drivers/gpu/drm/drm_plane.c
>@@ -62,6 +62,117 @@ static unsigned int drm_num_planes(struct drm_device *dev)
> 	return num;
> }
>
>+struct drm_format_modifier_blob {
>+#define FORMAT_BLOB_CURRENT 1
>+	/* Version of this blob format */
>+	u32 version;
>+
>+	/* Flags */
>+	u32 flags;
>+
>+	/* Number of fourcc formats supported */
>+	u32 count_formats;
>+
>+	/* Where in this blob the formats exist (in bytes) */
>+	u32 formats_offset;
>+
>+	/* Number of drm_format_modifiers */
>+	u32 count_modifiers;
>+
>+	/* Where in this blob the modifiers exist (in bytes) */
>+	u32 modifiers_offset;
>+
>+	/* u32 formats[] */
>+	/* struct drm_format_modifier modifiers[] */
>+} __packed;
>+
>+static inline u32 *
>+formats_ptr(struct drm_format_modifier_blob *blob)
>+{
>+	return (u32 *)(((char *)blob) + blob->formats_offset);
>+}
>+
>+static inline struct drm_format_modifier *
>+modifiers_ptr(struct drm_format_modifier_blob *blob)
>+{
>+	return (struct drm_format_modifier *)(((char *)blob) + blob->modifiers_offset);
>+}
>+
>+static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane,
>+				 const struct drm_plane_funcs *funcs,
>+				 const uint32_t *formats, unsigned int format_count,
>+				 const uint64_t *format_modifiers)
>+{
>+	const struct drm_mode_config *config = &dev->mode_config;
>+	const uint64_t *temp_modifiers = format_modifiers;
>+	unsigned int format_modifier_count = 0;
>+	struct drm_property_blob *blob = NULL;
>+	struct drm_format_modifier *mod;
>+	size_t blob_size = 0, formats_size, modifiers_size;
>+	struct drm_format_modifier_blob *blob_data;
>+	int i, j, ret = 0;
>+
>+	if (format_modifiers)
>+		while (*temp_modifiers++ != DRM_FORMAT_MOD_INVALID)
>+			format_modifier_count++;
>+
>+	formats_size = sizeof(__u32) * format_count;
>+	if (WARN_ON(!formats_size)) {
>+		/* 0 formats are never expected */
>+		return 0;
>+	}
>+
>+	modifiers_size =
>+		sizeof(struct drm_format_modifier) * format_modifier_count;
>+
>+	blob_size = ALIGN(sizeof(struct drm_format_modifier_blob), 8);
>+	blob_size += ALIGN(formats_size, 8);
>+	blob_size += modifiers_size;
>+
>+	blob = drm_property_create_blob(dev, blob_size, NULL);
>+	if (IS_ERR(blob))
>+		return -1;
>+
>+	blob_data = (struct drm_format_modifier_blob *)blob->data;
>+	blob_data->version = FORMAT_BLOB_CURRENT;
>+	blob_data->count_formats = format_count;
>+	blob_data->formats_offset = sizeof(struct drm_format_modifier_blob);
>+	blob_data->count_modifiers = format_modifier_count;
>+
>+	/* Modifiers offset is a pointer to a struct with a 64 bit field so it
>+	 * should be naturally aligned to 8B.
>+	 */
>+	blob_data->modifiers_offset =
>+		ALIGN(blob_data->formats_offset + formats_size, 8);
>+
>+	memcpy(formats_ptr(blob_data), formats, formats_size);
>+
>+	/* If we can't determine support, just bail */
>+	if (!funcs->format_mod_supported)
>+		goto done;
>+
>+	mod = modifiers_ptr(blob_data);
>+	for (i = 0; i < format_modifier_count; i++) {
>+		for (j = 0; j < format_count; j++) {
>+			if (funcs->format_mod_supported(plane, formats[j],
>+							format_modifiers[i])) {
>+				mod->formats |= 1 << j;
>+			}
>+		}
>+
>+		mod->modifier = format_modifiers[i];
>+		mod->offset = 0;
>+		mod->pad = 0;
>+		mod++;
>+	}
>+
>+done:
>+	drm_object_attach_property(&plane->base, config->modifiers,
>+				   blob->base.id);
>+
>+	return ret;
>+}
>+
> /**
>  * drm_universal_plane_init - Initialize a new universal plane object
>  * @dev: DRM device
>@@ -130,6 +241,10 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
> 		return -ENOMEM;
> 	}
>
>+	/* First driver to need more than 64 formats needs to fix this */
>+	if (WARN_ON(format_count > 64))
>+		return -EINVAL;
>+
> 	if (name) {
> 		va_list ap;
>
>@@ -177,6 +292,10 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
> 		drm_object_attach_property(&plane->base, config->prop_src_h, 0);
> 	}
>
>+	if (config->allow_fb_modifiers)
>+		create_in_format_blob(dev, plane, funcs, formats, format_count,
>+				      format_modifiers);
>+
> 	return 0;
> }
> EXPORT_SYMBOL(drm_universal_plane_init);
>diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
>index 42981711189b..03776e659811 100644
>--- a/include/drm/drm_mode_config.h
>+++ b/include/drm/drm_mode_config.h
>@@ -757,6 +757,12 @@ struct drm_mode_config {
> 	 */
> 	bool allow_fb_modifiers;
>
>+	/**
>+	 * @modifiers: Plane property to list support modifier/format
>+	 * combination.
>+	 */
>+	struct drm_property *modifiers;
>+
> 	/* cursor size */
> 	uint32_t cursor_width, cursor_height;
>
>diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>index 8c67fc03d53d..dcdd04c55792 100644
>--- a/include/uapi/drm/drm_mode.h
>+++ b/include/uapi/drm/drm_mode.h
>@@ -665,6 +665,32 @@ struct drm_mode_atomic {
> 	__u64 user_data;
> };
>
>+struct drm_format_modifier {
>+       /* Bitmask of formats in get_plane format list this info applies to. The
>+	* offset allows a sliding window of which 64 formats (bits).
>+	*
>+	* Some examples:
>+	* In today's world with < 65 formats, and formats 0, and 2 are
>+	* supported
>+	* 0x0000000000000005
>+	*		  ^-offset = 0, formats = 5
>+	*
>+	* If the number formats grew to 128, and formats 98-102 are
>+	* supported with the modifier:
>+	*
>+	* 0x0000003c00000000 0000000000000000
>+	*		  ^
>+	*		  |__offset = 64, formats = 0x3c00000000
>+	*
>+	*/
>+       uint64_t formats;
>+       uint32_t offset;
>+       uint32_t pad;
>+
>+       /* This modifier can be used with the format for this plane. */
>+       uint64_t modifier;
>+} __packed;
>+
> /**
>  * Create a new 'blob' data property, copying length bytes from data pointer,
>  * and returning new blob ID.
>-- 
>2.12.2
>
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