Invalid Argument under xilinx zcu102 platform

[wcy123]

I am new to DRM programming, this is an excellent example. Unfortunately, I could not get it work under zcu102 platform.

ret = drmModeSetCrtc(fd, iter->crtc, iter->fb, 0, 0,
                     &iter->conn, 1, &iter->mode);
if (ret)
            fprintf(stderr, "cannot set CRTC for connector %u (%d): %m\n",
                iter->conn, errno);

here ret is -22, it means "invalid argument".

I spent some time to investigate, by comparing it with modetest.c in libdrm, I modify the following lines, it works. But I don't know exactly why.

diff --git a/drm-howto/modeset.c b/drm-howto/modeset.c
index d2e56aa..58b2db5 100644
--- a/drm-howto/modeset.c
+++ b/drm-howto/modeset.c
@@ -447,7 +447,7 @@ static int modeset_create_fb(int fd, struct modeset_dev *dev)
        memset(&creq, 0, sizeof(creq));
        creq.width = dev->width;
        creq.height = dev->height;
-       creq.bpp = 32;
+       creq.bpp = 24;
        ret = drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &creq);
        if (ret < 0) {
                fprintf(stderr, "cannot create dumb buffer (%d): %m\n",
@@ -459,7 +459,7 @@ static int modeset_create_fb(int fd, struct modeset_dev *dev)
        dev->handle = creq.handle;

        /* create framebuffer object for the dumb-buffer */
-       ret = drmModeAddFB(fd, dev->width, dev->height, 24, 32, dev->stride,
+       ret = drmModeAddFB(fd, dev->width, dev->height, 24, 24, dev->stride,
                           dev->handle, &dev->fb);
        if (ret) {
                fprintf(stderr, "cannot create framebuffer (%d): %m\n",
@@ -630,6 +630,10 @@ static uint8_t next_color(bool *up, uint8_t cur, unsigned int mod)
  * beyond the scope of this document.
  */

+struct color_rgb24 {
+       unsigned int value:24;
+} __attribute__((__packed__));
+
 static void modeset_draw(void)
 {
        uint8_t r, g, b;
@@ -651,9 +655,9 @@ static void modeset_draw(void)
                for (iter = modeset_list; iter; iter = iter->next) {
                        for (j = 0; j < iter->height; ++j) {
                                for (k = 0; k < iter->width; ++k) {
-                                       off = iter->stride * j + k * 4;
-                                       *(uint32_t*)&iter->map[off] =
-                                                    (r << 16) | (g << 8) | b;
+                                       off = iter->stride * j + k * 3;
+                                        ((struct color_rgb24 *)&iter->map[off])
+                                            ->value = (r << 16) | (g << 8) | b;
                                 }
                         }
                }

[hai-yuan]

Thanks. this patch also worked for my case.

[ryecomp]

creq.bpp = 16

and

drmModeAddFB(fd, dev->width, dev->height, 16, 16, dev->stride

also works for me (in rk3399pro system)

[gaoweijun2017]

谢谢。该补丁也适用于我的情况。