"Antonino A. Daplas" <[email protected]> writes:
> David Eger is the author, the last I heard from him was 2 years ago.
> But I haven't received that many problem reports on cirrusfb.
Doesn't matter, what is important is that you know the stuff.
> The only register touched by the i2c code is EEPROM control (CL_SEQR8).
> This is never touched by the rest of the cirrusfb code. So I don't
> think concurrent access is a problem (unless the hardware has restrictions
> such as no other register accesses are allowed while this register is being
> accessed).
I mean I'm using (simplified):
unsigned char vga_rseq (void *regbase, unsigned char reg)
{
vga_w (regbase, VGA_SEQ_I, reg);
return vga_r (regbase, VGA_SEQ_D);
}
and
void vga_wseq (void *regbase, unsigned char reg, unsigned char val)
{
#ifdef VGA_OUTW_WRITE
vga_w_fast (regbase, VGA_SEQ_I, reg, val);
#else
vga_w (regbase, VGA_SEQ_I, reg);
vga_w (regbase, VGA_SEQ_D, val);
#endif /* VGA_OUTW_WRITE */
}
How do I know the following will not happen:
taskA) alpine_getsda() called from I2C subsystem
taskB) cirrusfb_blank() called from elsewhere
taskA) vga_rseq() calls vga_w()
taskB) vga_rseq() or _wseq() calls vga_w()
taskA) vga_r() performed with wrong index (set by taskB).
I see most of vga_[rw]seq() calls are at init/set_mode time but still
this could be a problem.
This question isn't limited to cirrusfb only, of course.
> The framebuffer layer is serialized by
> acquire_console_sem()/release_console_sem(). If you think concurrent access
> is a problem, you can always use that.
It's quite big... While I haven't investigated that, I rather thought
about some small lock for vga_rseq() and vga_wseq(). Not sure.
Another thing... How is access to VGA registers shared between
X11 and the framebuffer?
--
Krzysztof Halasa
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