I said I'd never blog

For the record, and because it gave me a hard time, here is how I could finally calibrate the touchscreen of an HTC TouchPro running hackable:1:

# rm -f /etc/pointercal
# export TSLIB_FBDEVICE=/dev/fb0
# export TSLIB_TSDEVICE=/dev/input/event3
# export TSLIB_CALIBFILE=/etc/pointercal
# export TSLIB_CONFFILE=/etc/ts.conf
# ts_calibrate

And the winner is:

# cat /etc/pointercal
-626 -42507 37731912 53487 254 -5420672 65536

I had to do this while running X, otherwise I only got trash on the framebuffer at best, and then nothing seemed to really happen.

Initially, I tried to find a way to understand and convert Android's data to the values expected by tslib. I started with the latter, and eventually gave up as these values seemed poorly documented at best: it essentially consisted in a couple mailing-list posts basically saying that "no, you should not generate calibration values yourself". But what if I have known, valid data?

Anyway, I could finally find some hints there:
http://doc.trolltech.com/4.3/qwscalibratedmousehandler.html#transform

And then in the source code for tslib:

plugins/linear.c, struct tslib_linear:
25 struct tslib_linear {
26         struct tslib_module_info module;
27         int     swap_xy;
28 
29 // Linear scaling and offset parameters for pressure
30         int     p_offset;
31         int     p_mult;
32         int     p_div;
34 // Linear scaling and offset parameters for x,y (can include rotation)
35         int     a[7];
36 };

plugins/linear.c, mod_init():
132         /*
133          * Check calibration file
134          */
135         if( (calfile = getenv("TSLIB_CALIBFILE")) == NULL) calfile = defaultcalfile;
136         if(stat(calfile,&sbuf)==0) {
137                 pcal_fd = open(calfile,O_RDONLY);
138                 read(pcal_fd,pcalbuf,200);
139                 lin->a[0] = atoi(strtok(pcalbuf," "));
140                 index=1;
141                 while(index<7) {
142                         tokptr = strtok(NULL," ");
143                         if(*tokptr!='\0') {
144                                 lin->a[index] = atoi(tokptr);
145                                 index++;
146                         }
147                 }

plugins/linear.c, linear_read():
53                         xtemp = samp->x; ytemp = samp->y;
54                         samp->x =       ( lin->a[2] +
55                                         lin->a[0]*xtemp +
56                                         lin->a[1]*ytemp ) / lin->a[6];
57                         samp->y =       ( lin->a[5] +
58                                         lin->a[3]*xtemp +
59                                         lin->a[4]*ytemp ) / lin->a[6];

Credits go there:
http://automon.donaloconnor.net/installing-tslib-and-calibrating-it/83/