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 <tzimmerm...@suse.de>
Reviewed-by: Sam Ravnborg <s...@ravnborg.org>
Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
---
 drivers/gpu/drm/drm_format_helper.c | 108 ++++++++++++++++++++++++++++
 drivers/gpu/drm/tiny/simpledrm.c    |  47 ++----------
 include/drm/drm_format_helper.h     |  11 ++-
 3 files changed, 123 insertions(+), 43 deletions(-)

diff --git a/drivers/gpu/drm/drm_format_helper.c 
b/drivers/gpu/drm/drm_format_helper.c
index 56642816fdff..4afc4ac27342 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/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);
diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
index 404290760c60..777ccd250871 100644
--- a/drivers/gpu/drm/tiny/simpledrm.c
+++ b/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)
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index caa181194335..eb5c98cf82b8 100644
--- a/include/drm/drm_format_helper.h
+++ b/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 */
-- 
2.37.2

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