/* fbpantest2.c — does fb0 actually PAN? Print ioctl return + errno.
 * Key question: is the display pannable via FBIOPAN_DISPLAY/FBIOPUT_VSCREENINFO,
 * or is the double buffer flipped by direct LCDC register writes (desar) that
 * the fb var yoffset never reflects?
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <stdint.h>

#define GETV 0x4600

static int get_info(int fd, uint32_t *yoff, uint32_t *yres) {
    unsigned char v[160]; memset(v,0,sizeof v);
    if (ioctl(fd, GETV, v) < 0) return -1;
    *yres = *(uint32_t*)(v + 4);
    *yoff = *(uint32_t*)(v + 20);
    return 0;
}

int main(void) {
    int fd = open("/dev/fb0", O_RDWR);
    if (fd < 0) { perror("open"); return 1; }
    uint32_t orig=0,yres=0; get_info(fd,&orig,&yres);
    uint32_t target=(orig<yres)?yres:0;
    printf("orig yoffset=%u yres=%u target=%u\n", orig,yres,target);

    unsigned char v[160];
    memset(v,0,sizeof v);
    ioctl(fd, GETV, v);
    *(uint32_t*)(v+16)=0; *(uint32_t*)(v+20)=target;
    v[84]=0; /* activate = 0 (implies activate-on-next?) */

    errno=0;
    int r6=ioctl(fd, 0x4606, v);
    int e6=errno; errno=0;
    uint32_t now=0; get_info(fd,&now,&yres);
    printf("PAN_DISPLAY(0x4606) r=%d errno=%d(%s) -> yoffset now %u\n", r6,e6,strerror(e6),now);
    if (now==target) { errno=0; ioctl(fd,0x4606,v); /* restore */ }

    /* now try PUT_VSCREENINFO with activate=FB_ACTIVATE_NOW */
    memset(v,0,sizeof v); ioctl(fd, GETV, v);
    *(uint32_t*)(v+16)=0; *(uint32_t*)(v+20)=target;
    errno=0;
    int r1=ioctl(fd, 0x4601, v);
    int e1=errno; errno=0;
    get_info(fd,&now,&yres);
    printf("PUT_VSCREENINFO(0x4601) r=%d errno=%d(%s) -> yoffset now %u\n", r1,e1,strerror(e1),now);
    if (now==target) { memset(v,0,sizeof v); ioctl(fd,GETV,v); *(uint32_t*)(v+16)=0; *(uint32_t*)(v+20)=orig; ioctl(fd,0x4601,v); }

    /* getid; also read FBIOGET_DISPINFO(0x4618) */
    unsigned char d[256]; memset(d,0,sizeof d);
    errno=0;
    int rd=ioctl(fd, 0x4618, d);
    int ed=errno;
    printf("GET_DISPINFO(0x4618) r=%d errno=%d(%s)\n", rd, ed, strerror(ed));
    for (unsigned i=0;i<64;i+=4){ if (*(uint32_t*)(d+i)) printf("   d[%u]=%08x\n", i, *(uint32_t*)(d+i)); }
    close(fd);
    return 0;
}