drm/ast: astdp: Look up mode index from table

Replace the large switch statement with a look-up table when selecting
the mode index. Makes the code easier to read. The table is sorted by
resolutions; if run-time overhead from traversal becomes significant,
binary search would be a possible optimization.

The mode index requires a refresh-rate index to be added or subtracted,
which still requires a minimal switch. In the original code, some of
the indices did not contain this computation. Those cases would have been
equivalent to adding 0, so they are now all subsumed in the switch's
default branch.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Suggested-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
v3:
- explain the semantics of the new switch statement (Jocelyn)
Link: https://patchwork.freedesktop.org/patch/msgid/20250131092257.115596-15-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c
index 3f5e586325a982366d6970c933188d1bc2405c4c..54b5a350a988d5a512971305b4fb2511d682e7ef 100644 (file)
--- a/drivers/gpu/drm/ast/ast_dp.c
+++ b/drivers/gpu/drm/ast/ast_dp.c
@@ -14,80 +14,74 @@
 #include "ast_drv.h"
 #include "ast_vbios.h"
 
+struct ast_astdp_mode_index_table_entry {
+       unsigned int hdisplay;
+       unsigned int vdisplay;
+       unsigned int mode_index;
+};
+
+/* FIXME: Do refresh rate and flags actually matter? */
+static const struct ast_astdp_mode_index_table_entry ast_astdp_mode_index_table[] = {
+       {  320,  240, ASTDP_320x240_60 },
+       {  400,  300, ASTDP_400x300_60 },
+       {  512,  384, ASTDP_512x384_60 },
+       {  640,  480, ASTDP_640x480_60 },
+       {  800,  600, ASTDP_800x600_56 },
+       { 1024,  768, ASTDP_1024x768_60 },
+       { 1152,  864, ASTDP_1152x864_75 },
+       { 1280,  800, ASTDP_1280x800_60_RB },
+       { 1280, 1024, ASTDP_1280x1024_60 },
+       { 1360,  768, ASTDP_1366x768_60 }, // same as 1366x786
+       { 1366,  768, ASTDP_1366x768_60 },
+       { 1440,  900, ASTDP_1440x900_60_RB },
+       { 1600,  900, ASTDP_1600x900_60_RB },
+       { 1600, 1200, ASTDP_1600x1200_60 },
+       { 1680, 1050, ASTDP_1680x1050_60_RB },
+       { 1920, 1080, ASTDP_1920x1080_60 },
+       { 1920, 1200, ASTDP_1920x1200_60 },
+       { 0 }
+};
+
+static int __ast_astdp_get_mode_index(unsigned int hdisplay, unsigned int vdisplay)
+{
+       const struct ast_astdp_mode_index_table_entry *entry = ast_astdp_mode_index_table;
+
+       while (entry->hdisplay && entry->vdisplay) {
+               if (entry->hdisplay == hdisplay && entry->vdisplay == vdisplay)
+                       return entry->mode_index;
+               ++entry;
+       }
+
+       return -EINVAL;
+}
+
 static int ast_astdp_get_mode_index(const struct ast_vbios_enhtable *vmode)
 {
+       int mode_index;
        u8 refresh_rate_index;
 
+       mode_index = __ast_astdp_get_mode_index(vmode->hde, vmode->vde);
+       if (mode_index < 0)
+               return mode_index;
+
        if (vmode->refresh_rate_index < 1 || vmode->refresh_rate_index > 255)
                return -EINVAL;
-
        refresh_rate_index = vmode->refresh_rate_index - 1;
 
-       switch (vmode->hde) {
-       case 320:
-               if (vmode->vde == 240)
-                       return ASTDP_320x240_60;
-               break;
-       case 400:
-               if (vmode->vde == 300)
-                       return ASTDP_400x300_60;
-               break;
-       case 512:
-               if (vmode->vde == 384)
-                       return ASTDP_512x384_60;
-               break;
-       case 640:
-               if (vmode->vde == 480)
-                       return (u8)(ASTDP_640x480_60 + (u8)refresh_rate_index);
-               break;
-       case 800:
-               if (vmode->vde == 600)
-                       return (u8)(ASTDP_800x600_56 + (u8)refresh_rate_index);
-               break;
-       case 1024:
-               if (vmode->vde == 768)
-                       return (u8)(ASTDP_1024x768_60 + (u8)refresh_rate_index);
-               break;
-       case 1152:
-               if (vmode->vde == 864)
-                       return ASTDP_1152x864_75;
-               break;
-       case 1280:
-               if (vmode->vde == 800)
-                       return (u8)(ASTDP_1280x800_60_RB - (u8)refresh_rate_index);
-               if (vmode->vde == 1024)
-                       return (u8)(ASTDP_1280x1024_60 + (u8)refresh_rate_index);
-               break;
-       case 1360:
-       case 1366:
-               if (vmode->vde == 768)
-                       return ASTDP_1366x768_60;
-               break;
-       case 1440:
-               if (vmode->vde == 900)
-                       return (u8)(ASTDP_1440x900_60_RB - (u8)refresh_rate_index);
-               break;
-       case 1600:
-               if (vmode->vde == 900)
-                       return (u8)(ASTDP_1600x900_60_RB - (u8)refresh_rate_index);
-               if (vmode->vde == 1200)
-                       return ASTDP_1600x1200_60;
-               break;
-       case 1680:
-               if (vmode->vde == 1050)
-                       return (u8)(ASTDP_1680x1050_60_RB - (u8)refresh_rate_index);
-               break;
-       case 1920:
-               if (vmode->vde == 1080)
-                       return ASTDP_1920x1080_60;
-               if (vmode->vde == 1200)
-                       return ASTDP_1920x1200_60;
+       /* FIXME: Why are we doing this? */
+       switch (mode_index) {
+       case ASTDP_1280x800_60_RB:
+       case ASTDP_1440x900_60_RB:
+       case ASTDP_1600x900_60_RB:
+       case ASTDP_1680x1050_60_RB:
+               mode_index = (u8)(mode_index - (u8)refresh_rate_index);
                break;
        default:
+               mode_index = (u8)(mode_index + (u8)refresh_rate_index);
                break;
        }
 
-       return -EINVAL;
+       return mode_index;
 }
 
 static bool ast_astdp_is_connected(struct ast_device *ast)