Bug#342053: Boot-time script to disable DFB's HW acceleration

[Sven Luther <sven.luther@wanadoo.fr>]

On Tue, Dec 13, 2005 at 01:02:04PM +0100, Attilio Fiandrotti wrote:
> Sven Luther wrote:
> >>	echo "no-hardware" >>/etc/directfbrc
> >>else
> >>	for driver in $BAD_LIST; do
> >>		if [ $(dmesg|grep $driver |wc -w) -gt 0 ];then
> >
> >
> >I am not sure if dmesg + grep + wc is the best way to do this, but i also
> >don't know how to best map the /proc/fb entries to module names, but we 
> >have
> >this one, as well as : 
> >
> >  /sys/bus/pci/drivers/adeonfb/0000\:00\:10.0/graphics\:fb0
> >
> >Which needs a 2.6 kernel though, but i don't think we are building 2.4
> >graphical d-i anyway.
> 
> ok, so i suppose checking if /sys/bus/pci/drivers/<broken fbdev device> 

Yep, in the general case, it should be possible to have multiple graphic
cards, and the broken one not being the one used for booting d-i.

Also, of interest is : 

/sys/class/graphics/fb0, which has a device/driver symlink to the above path
you suggest, but i don't know how to find the radeonfb driver name information
from this one, which sucks.

> exist is enough to tell if HW acceleration has to be disabled.
> Below is the same script reworked after your and Geert Stappers's 
> corrections.
> The user, to manually disable DFB HW acceleration, should boot with 
> something like "install NO_DFB_ACCELERATION=TRUE" and this should be 
> documented in the d-i manual and/or in the help screen that you see when 
> you press F2 at boot time.

Yeah, altough i prefer the lower-case new option format thingy, but maybe they
are reserved for debconf variables ? dfb/no_accel=true ? Do we have access to
debconf already at this early stage ?

> Where this piece of code should be collocated? inside a new "Sxx.sh" 
> script or should be better appended to 
> /lib/debian-installer.d/S35framebuffer-linux or some other already 
> existing script?

Not sure, it has to run early enough (before gtkdi is launched) and late
enough (after the framebuffer drivers have been loaded.

Maybe adding ti to S35framebuffer-linux is a good thing.

> Note that the list of bad fbdev deviced is hardcoded inside this script: 
> is this a good idea? but i have no idea of where else those could be 
> listed..

It should be a preseedable debconf value maybe, not sure, see my above
comment, dfb/bad_fbdevs="nvidiafb atyfb" would be a good idea. Maybe we could
reverse the script and whitelist the known good graphic cards though, with :
dfb/good_fbdevs="radeonfb vesafb" ?

Friendly,

Sven Luther