V4L/DVB (10567): bttv: shrink muxsel data in card database
Over half of the card database was used to store muxsel data. 64 bytes
were used to store one 32 bit word for each of up to 16 inputs.
The Bt8x8 only has two bits to control its mux, so muxsel data for 16
inputs will fit into a single 32 bit word. There were a couple cards that
had special muxsel data that didn't fit in two bits, but I cleaned them up
in earlier patches.
Unfortunately, C doesn't allow us to have an array of bit fields. This
makes initializing the structure more of a pain. But with some cpp magic,
we can do it by changing:
.muxsel = { 2, 3, 0, 1 },
.muxsel = { 2, 2, 2, 2, 3, 3, 3, 3, 1, 1 },
Into:
.muxsel = MUXSEL(2, 3, 0, 1),
.muxsel = MUXSEL(2, 2, 2, 2, 3, 3, 3, 3, 1, 1),
That's not so bad. MUXSEL is a fancy macro that packs the arguments (of
which there can be one to sixteen!) into a single word two bits at a time.
It's a compile time constant (a variadic function wouldn't be) so we can
use it to initialize the structure. It's important the the arguments to
the macro only be plain decimal integers. Stuff like "0x01", "(2)", or
"MUX3" won't work properly.
I also created an accessor function, bttv_muxsel(btv, input), that gets the
mux bits for the selected input. It makes it cleaner to change the way the
muxsel data is stored.
This patch doesn't change the code size and decreases the datasegment by
9440 bytes.
Signed-off-by: 
Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: 
Mauro Carvalho Chehab <mchehab@redhat.com>
Showing
Please register or sign in to comment