Update FB initialization to use mbox instead of structs

The framebuffer initialization was breaking randomly, I suspect because
the memory access of the static fb_request was not 16 bit aligned. For
simplicity, I went back to the volatile mbox array implementation.

Additionally, now on fb_init the rgb order is requested to properly
adjust the palette on docolors.

3 files changed, 72 insertions, 93 deletions

diff --git a/src/common.h b/src/common.h
index ad3aad8..0057950 100644
--- a/src/common.h
+++ b/src/common.h
@@ -171,40 +171,6 @@ uart_hex(unsigned int d) {
 // VideoCore Mailboxes.
 //
 
-typedef struct MboxTagHeader {
-    u32 id;
-    u32 buf_size;
-    u32 code;
-} MboxTagHeader;
-
-typedef struct MboxScreenTag {
-    MboxTagHeader header;
-    u32 width;
-    u32 height;
-} MboxScreenTag;
-
-typedef struct MboxDepthTag {
-    MboxTagHeader header;
-    u32 depth;
-} MboxDepthTag;
-
-typedef struct MboxFramebufferTag {
-    MboxTagHeader header;
-    u32 fb_addr;
-    u32 fb_size;
-} MboxFramebufferTag;
-
-typedef struct MboxFramebufferRequest {
-    u32 buf_size;
-    u32 code;
-    MboxScreenTag screen_tag;
-    MboxScreenTag virtual_screen_tag;
-    MboxDepthTag depth_tag;
-    MboxFramebufferTag framebuffer_tag;
-    u32 end_tag;
-    u8 padding[8];
-} MboxFramebufferRequest;
-
 typedef struct MailboxRegs {
     vu32 read;
     vu32 reserved[5];
@@ -236,10 +202,21 @@ typedef enum MboxChannels {
 #define MBOX_FULL  0x80000000
 #define MBOX_EMPTY 0x40000000
 
+// Mailbox tags.
+#define  MBOX_TAG_SET_SCREEN  0x48003
+#define  MBOX_TAG_SET_VSCREEN 0x48004
+#define  MBOX_TAG_SET_DEPTH   0x48005
+#define  MBOX_TAG_SET_RGB     0x48006
+#define  MBOX_TAG_GET_FB      0x40001
+#define  MBOX_TAG_END         0
+
+// Mailbox request buffer. Needs to be 16 bit aligned to avoid issues.
+volatile u32 __attribute__((aligned(16))) mbox[64];
+
 static inline void
-mb_write(u8 channel, void *data) {
+mb_write(u8 channel) {
     while (MBOX->status & MBOX_FULL);
-    MBOX->write = ((uintptr_t)data & ~0xF) | (channel & 0xF);
+    MBOX->write = ((uintptr_t)mbox & ~0xF) | (channel & 0xF);
 }
 
 static inline u32
@@ -254,8 +231,8 @@ mb_read(u8 channel) {
 }
 
 static inline int
-mb_call(unsigned char ch, void *msg) {
-    mb_write(ch, msg);
+mb_call(unsigned char ch) {
+    mb_write(ch);
     return mb_read(ch);
 }
 
diff --git a/src/main.c b/src/main.c
index c379ace..1853192 100644
--- a/src/main.c
+++ b/src/main.c
@@ -40,15 +40,11 @@ docolors(Device *d) {
         u8 g = ((d->dat[0xa + i / 2] >> (!(i % 2) << 2)) & 0x0f) * 0x11;
         u8 b = ((d->dat[0xc + i / 2] >> (!(i % 2) << 2)) & 0x0f) * 0x11;
 
-        // NOTE: This is a bit of a hack. We probably want to check the RGB byte
-        // order on the mailbox request.
-#if RPI_VERSION == 3
-        palette[i] = (b << 16) | (g << 8) | r;
-#endif
-
-#if RPI_VERSION == 4
-        palette[i] = (r << 16) | (g << 8) | b;
-#endif
+        if (rgb_order) {
+            palette[i] = (b << 16) | (g << 8) | r;
+        } else {
+            palette[i] = (r << 16) | (g << 8) | b;
+        }
     }
     for(size_t i = 4; i < 16; ++i) {
         palette[i] = palette[i / 4];
diff --git a/src/ppu.c b/src/ppu.c
index e153c4d..ac0feeb 100644
--- a/src/ppu.c
+++ b/src/ppu.c
@@ -24,6 +24,7 @@ static u32 palette[16];
 static u8 pixels_buf[SCREEN_WIDTH * SCREEN_HEIGHT];
 static u8 dirty_lines[SCREEN_HEIGHT];
 static u8 reqdraw = 0;
+static u32 rgb_order;
 
 static Uint8 blending[5][16] = {
     {0, 0, 0, 0, 1, 0, 1, 1, 2, 2, 0, 2, 3, 3, 3, 0},
@@ -84,57 +85,62 @@ redraw_screen(void) {
     }
 }
 
+void
+fb_init(void) {
+    mbox[0] = 25 * 4;
+    mbox[1] = MBOX_REQUEST;
+
+    // Screen request.
+    mbox[2] = MBOX_TAG_SET_SCREEN;
+    mbox[3] = 8;
+    mbox[4] = 0;
+    mbox[5] = SCREEN_WIDTH;
+    mbox[6] = SCREEN_HEIGHT;
+
+    // Virtual screen.
+    mbox[7] = MBOX_TAG_SET_VSCREEN;
+    mbox[8] = 8;
+    mbox[9] = 0;
+    mbox[10] = SCREEN_WIDTH;
+    mbox[11] = SCREEN_HEIGHT;
+
+    // Bit depth.
+    mbox[12] = MBOX_TAG_SET_DEPTH;
+    mbox[13] = 4;
+    mbox[14] = 0;
+    mbox[15] = 32;
+
+    // RGB order.
+    mbox[16] = MBOX_TAG_SET_RGB;
+    mbox[17] = 4;
+    mbox[18] = 0;
+    mbox[19] = 1;
+
+    // Framebuffer request.
+    mbox[20] = MBOX_TAG_GET_FB;
+    mbox[21] = 8;
+    mbox[22] = 0;
+    mbox[23] = 0;
+    mbox[24] = 0;
+
+    // End tag.
+    mbox[25] = MBOX_TAG_END;
+
+    if (mb_call(MBOX_CH_PROP) && mbox[15] == 32 && mbox[23] != 0) {
+        framebuffer = (u32*)((uintptr_t)(mbox[23]) & 0x3FFFFFFF);
+        rgb_order = mbox[19];
+        uart_puts("Framebuffer initialized\n");
+    } else {
+        uart_puts("Unable to initialize framebuffer\n");
+    }
+}
+
 int
 ppu_init(Ppu *p, Uint8 hor, Uint8 ver) {
     p->width = 8 * hor;
     p->height = 8 * ver;
 
-    // Initialize the framebuffer.
-    static MboxFramebufferRequest fb_request = {
-        .buf_size = 96,
-        .code = MBOX_REQUEST,
-        .screen_tag = {
-            .header = {
-                .id = 0x48003,
-                .buf_size = 8,
-            },
-            .width = SCREEN_WIDTH,
-            .height = SCREEN_HEIGHT,
-        },
-        .virtual_screen_tag = {
-            .header = {
-                .id = 0x48004,
-                .buf_size = 8,
-            },
-            .width = SCREEN_WIDTH,
-            .height = SCREEN_HEIGHT,
-        },
-        .depth_tag = {
-            .header = {
-                .id = 0x48005,
-                .buf_size = 4,
-            },
-            .depth = 32,
-        },
-        .framebuffer_tag = {
-            .header = {
-                .id = 0x40001,
-                .buf_size = 8,
-            },
-            .fb_addr = 0,
-            .fb_size = 0,
-        }
-    };
-
-    if (mb_call(MBOX_CH_PROP, &fb_request)
-            && fb_request.depth_tag.depth == 32
-            && fb_request.framebuffer_tag.fb_addr != 0) {
-        fb_request.framebuffer_tag.fb_addr &= 0x3FFFFFFF;
-        framebuffer = (u32*)((uintptr_t)fb_request.framebuffer_tag.fb_addr);
-    } else {
-        uart_puts("Unable initialize framebuffer\n");
-        return 0;
-    }
+    fb_init();
 
     p->pixels = pixels_buf;