drm/format-helper: Add drm_fb_build_fourcc_list() helper

Add drm_fb_build_fourcc_list() function that builds a list of supported
formats from native and emulated ones. Helpful for all drivers that do
format conversion as part of their plane updates. Update current caller.

v3:
	* improve warnings on ignored formats (Sam)
v2:
	* use u32 instead of uint32_t (Sam)
	* print a warning if output array is too small (Sam)
	* comment fixes (Sam)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905141648.22013-5-tzimmermann@suse.de

drivers/gpu/drm/drm_format_helper.c

@@ -793,3 +793,111 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 	kfree(src32);
 }
 EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono);
+
+static bool is_listed_fourcc(const uint32_t *fourccs, size_t nfourccs, uint32_t fourcc)
+{
+	const uint32_t *fourccs_end = fourccs + nfourccs;
+
+	while (fourccs < fourccs_end) {
+		if (*fourccs == fourcc)
+			return true;
+		++fourccs;
+	}
+	return false;
+}
+
+/**
+ * drm_fb_build_fourcc_list - Filters a list of supported color formats against
+ *                            the device's native formats
+ * @dev: DRM device
+ * @native_fourccs: 4CC codes of natively supported color formats
+ * @native_nfourccs: The number of entries in @native_fourccs
+ * @driver_fourccs: 4CC codes of all driver-supported color formats
+ * @driver_nfourccs: The number of entries in @driver_fourccs
+ * @fourccs_out: Returns 4CC codes of supported color formats
+ * @nfourccs_out: The number of available entries in @fourccs_out
+ *
+ * This function create a list of supported color format from natively
+ * supported formats and the emulated formats.
+ * At a minimum, most userspace programs expect at least support for
+ * XRGB8888 on the primary plane. Devices that have to emulate the
+ * format, and possibly others, can use drm_fb_build_fourcc_list() to
+ * create a list of supported color formats. The returned list can
+ * be handed over to drm_universal_plane_init() et al. Native formats
+ * will go before emulated formats. Other heuristics might be applied
+ * to optimize the order. Formats near the beginning of the list are
+ * usually preferred over formats near the end of the list.
+ *
+ * Returns:
+ * The number of color-formats 4CC codes returned in @fourccs_out.
+ */
+size_t drm_fb_build_fourcc_list(struct drm_device *dev,
+				const u32 *native_fourccs, size_t native_nfourccs,
+				const u32 *driver_fourccs, size_t driver_nfourccs,
+				u32 *fourccs_out, size_t nfourccs_out)
+{
+	u32 *fourccs = fourccs_out;
+	const u32 *fourccs_end = fourccs_out + nfourccs_out;
+	bool found_native = false;
+	size_t i;
+
+	/*
+	 * The device's native formats go first.
+	 */
+
+	for (i = 0; i < native_nfourccs; ++i) {
+		u32 fourcc = native_fourccs[i];
+
+		if (is_listed_fourcc(fourccs_out, fourccs - fourccs_out, fourcc)) {
+			continue; /* skip duplicate entries */
+		} else if (fourccs == fourccs_end) {
+			drm_warn(dev, "Ignoring native format %p4cc\n", &fourcc);
+			continue; /* end of available output buffer */
+		}
+
+		drm_dbg_kms(dev, "adding native format %p4cc\n", &fourcc);
+
+		if (!found_native)
+			found_native = is_listed_fourcc(driver_fourccs, driver_nfourccs, fourcc);
+		*fourccs = fourcc;
+		++fourccs;
+	}
+
+	/*
+	 * The plane's atomic_update helper converts the framebuffer's color format
+	 * to a native format when copying to device memory.
+	 *
+	 * If there is not a single format supported by both, device and
+	 * driver, the native formats are likely not supported by the conversion
+	 * helpers. Therefore *only* support the native formats and add a
+	 * conversion helper ASAP.
+	 */
+	if (!found_native) {
+		drm_warn(dev, "Format conversion helpers required to add extra formats.\n");
+		goto out;
+	}
+
+	/*
+	 * The extra formats, emulated by the driver, go second.
+	 */
+
+	for (i = 0; (i < driver_nfourccs) && (fourccs < fourccs_end); ++i) {
+		u32 fourcc = driver_fourccs[i];
+
+		if (is_listed_fourcc(fourccs_out, fourccs - fourccs_out, fourcc)) {
+			continue; /* skip duplicate and native entries */
+		} else if (fourccs == fourccs_end) {
+			drm_warn(dev, "Ignoring emulated format %p4cc\n", &fourcc);
+			continue; /* end of available output buffer */
+		}
+
+		drm_dbg_kms(dev, "adding emulated format %p4cc\n", &fourcc);
+
+		*fourccs = fourcc;
+		++fourccs;
+	}
+
+out:
+	return fourccs - fourccs_out;
+}
+EXPORT_SYMBOL(drm_fb_build_fourcc_list);

drivers/gpu/drm/tiny/simpledrm.c

@@ -644,45 +644,6 @@ static struct drm_display_mode simpledrm_mode(unsigned int width,
 	return mode;
 }
 
-static const uint32_t *simpledrm_device_formats(struct simpledrm_device *sdev,
-						size_t *nformats_out)
-{
-	struct drm_device *dev = &sdev->dev;
-	size_t i;
-
-	if (sdev->nformats)
-		goto out; /* don't rebuild list on recurring calls */
-
-	/* native format goes first */
-	sdev->formats[0] = sdev->format->format;
-	sdev->nformats = 1;
-
-	/* default formats go second */
-	for (i = 0; i < ARRAY_SIZE(simpledrm_primary_plane_formats); ++i) {
-		if (simpledrm_primary_plane_formats[i] == sdev->format->format)
-			continue; /* native format already went first */
-		sdev->formats[sdev->nformats] = simpledrm_primary_plane_formats[i];
-		sdev->nformats++;
-	}
-
-	/*
-	 * TODO: The simpledrm driver converts framebuffers to the native
-	 * format when copying them to device memory. If there are more
-	 * formats listed than supported by the driver, the native format
-	 * is not supported by the conversion helpers. Therefore *only*
-	 * support the native format and add a conversion helper ASAP.
-	 */
-	if (drm_WARN_ONCE(dev, i != sdev->nformats,
-			  "format conversion helpers required for %p4cc",
-			  &sdev->format->format)) {
-		sdev->nformats = 1;
-	}
-
-out:
-	*nformats_out = sdev->nformats;
-	return sdev->formats;
-}
-
 static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 							struct platform_device *pdev)
 {
@@ -699,7 +660,6 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 	struct drm_encoder *encoder;
 	struct drm_connector *connector;
 	unsigned long max_width, max_height;
-	const uint32_t *formats;
 	size_t nformats;
 	int ret;
 
@@ -811,11 +771,14 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 
 	/* Primary plane */
 
-	formats = simpledrm_device_formats(sdev, &nformats);
+	nformats = drm_fb_build_fourcc_list(dev, &format->format, 1,
+					    simpledrm_primary_plane_formats,
+					    ARRAY_SIZE(simpledrm_primary_plane_formats),
+					    sdev->formats, ARRAY_SIZE(sdev->formats));
 
 	primary_plane = &sdev->primary_plane;
 	ret = drm_universal_plane_init(dev, primary_plane, 0, &simpledrm_primary_plane_funcs,
-				       formats, nformats,
+				       sdev->formats, nformats,
 				       simpledrm_primary_plane_format_modifiers,
 				       DRM_PLANE_TYPE_PRIMARY, NULL);
 	if (ret)

include/drm/drm_format_helper.h

@@ -6,11 +6,15 @@
 #ifndef __LINUX_DRM_FORMAT_HELPER_H
 #define __LINUX_DRM_FORMAT_HELPER_H
 
-struct iosys_map;
+#include <linux/types.h>
+
+struct drm_device;
 struct drm_format_info;
 struct drm_framebuffer;
 struct drm_rect;
 
+struct iosys_map;
+
 unsigned int drm_fb_clip_offset(unsigned int pitch, const struct drm_format_info *format,
 				const struct drm_rect *clip);
 
@@ -44,4 +48,9 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
 			     const struct iosys_map *src, const struct drm_framebuffer *fb,
 			     const struct drm_rect *clip);
 
+size_t drm_fb_build_fourcc_list(struct drm_device *dev,
+				const u32 *native_fourccs, size_t native_nfourccs,
+				const u32 *extra_fourccs, size_t extra_nfourccs,
+				u32 *fourccs_out, size_t nfourccs_out);
+
 #endif /* __LINUX_DRM_FORMAT_HELPER_H */