Re: Some thoughts on Rage128/Radeon EDID

On Sun, 2003-08-17 at 08:32, Jon Smirl wrote:

I looked through the 2.4 radeon driver and I see all
of the code for parsing the EDID blocks. This is a lot
of code and it is seldom used (compared to something
like an interrupt handler).

Yup. Which is a reason, btw, why a think the radeon driver
should be split into multiple files (and possibly share
some code with aty128), but I haven't had time to play with
that much.

Somewhat complete I2C driver code exists in the KATOS
project.
http://www.core.binghamton.edu/~insomnia/gatos/katos/src/katos-0.5.tar.gz

These next thoughts just apply to 2.6, not 2.4.

There are a lot of things on the I2C bus on the these
cards: EDID,  video capture, teletext, tv out and mpeg
decoding control, etc..

1) How about making the fb driver register itself as
an I2C bus so that it appears in /proc/bus/I2C? I've
never touched I2C code so I don't know what this
involves.

I don't much like the Linux i2c layer because I think it's bloated
and not very convenient to use, but if you want to go that way, then
it's ok ;) Whatever i2c API we expose, be it custom or via the linux
i2c layer...

2) Making the card appear in /proc/bus/I2C makes it
easy to get to from user space.  A user level app can
read the EDID info, diff it off against card
capabilities and IOCTL the new mode in. Maybe modify
fbset.

Well... I'd rather have an in-kernel monitor "driver" module that
would access the EDID to provide a default mode, validate modes
etc... It could expose the raw EDID data via sysfs. We want proper
mode detection & probing at boot time. Note that the linux i2c
layer also allows for in-kernel clients, not only userland interface.
 

3) Doesn't the video hardware always power on to a
visible state? So setting an alternate mode can wait
until we can run user space apps. I'm not sure it is
worth all of the kernel code  just to get a 50 line
display with valid EDID during the first few seconds
of boot.

Unfortunately, not all cards power on with a visible state... Well,
in most cases they do, and we have offb on powermac to use as a basic
text console (since we don't have VGA text mode), so we could eventually
have this transition done later on.

4) Once we have access to the other devices maybe
people will write apps that use them.

Maybe... I see your point in wanting to expose those i2c busses
to userland. I think it makes sense for things like teletext or tv out
control. But I still prefer having monitor & edid management be an
in-kernel driver (same for capture btw).

Ben.



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