Re: [PATCH] DDC2/I2C Support

["Antonino A. Daplas" <adaplas@softhome.net>]

On Tuesday 06 January 2004 05:59, Benjamin Herrenschmidt wrote:

>
> So you choose to get away from the linux i2c infrastructure ?

I already looked at your tree.  After some thought, I agree with both of you 
(Kronos) that i2c/ddc2 should be driver specific.  I'll remove the generic 
fbi2c interface.

>
> > 2. [fbmon.c]: Consolidated different ways of getting EDID with the
> > following function:
> >
> > 	unsigned char *fb_get_edid(struct fb_info *info, struct pci_dev *pdev,
> > int what)
> >
> > 		the parameter "what" can be:
> > 			EDID_DDC2 - get EDID via DDC2/I2C fb_get_edid_from_ddc2()
> >			EDID_ARCH - get	EDID via BIOS or OF get_EDID_from_{OF|BIOS}()
>
> The later is very card-specific... I don't think it can be abstracted.
> Also, if you look at the new radeonfb, you'll notice that the BIOS
> search has actually more than one way of getting to the EDID and
> may gather more than just the EDID (panel power delay, panel fixed
> dividers, etc...) Also, the OF parsing code cannot easily be abstracted
> as the OF driver for different type of cards do things differently.
>
> Hrm... reading your actual patch, I see that you are actually doing
> this BIOS call to get it, not parsing the BIOS image. Ok, that may
> be interesting...
>

There was the patch I submitted some 8 months ago and has been in the kernel 
since linux-2.5.x.  For X86, it will get the EDID block via VBE calls before 
the kernel goes to protected mode.  This is used by get_EDID_from_BIOS() in 
fbmon.c. Actual code is in boot/arch/i386/boot/video.S[store_edid]

Currently, it's always compiled in and some people reported problems with it 
(like taking 5 minutes to boot - probably BIOS using DDC1). I just added a 
kernel config for it so people can choose to compile it out.  However, with 
most drivers still not having DDC/I2C support, it's an easy way of getting 
the EDID block.

> Also, the former need a way to tell on which port we want the EDID,
> and the EDID code may need a bit more than juts that "get EDID" (look
> the other bit banging done to the i2c registers in radeonfb).
>
> I'd actually keep all that in the driver...
>
> > 	2.a getting EDID from the BIOS is now configurable (CONFIG_EDID_BIOS)
> > since some people reported problems during booting or it takes a long
> > time for the process to finish.
>
> This is about using the VESA BIOS at boot or scanning the ROM image ?

This is about getting the EDID using VBE calls while in real mode. 

>
> > 4. [fbmon.c]: Extended struct fb_monspecs to include display information
> > specified in EDID.
> >
> > 	Use function
> > 		void fb_get_monspecs(unsigned char *edid, struct fb_monspecs *specs)
>
>  .../...
>
> Can we define a "parsed_EDID" structure or whatever we call it that
> contains the list of modes, the monspecs, and other informations
> obtained from the EDID all at once ? I also need the display model
> name and vendor for example (to deal with some "fixups"). it would
> be convenient to have one single parsing pass extracting all the
> informations to one structure...
>

Ok, this should not be hard.

> > --------------------------------------------------------
> >
> > 5. [fbcon.c]: Minor fixes on the cursor and scrolling.
>
> That pops up something else in my mind... Shouldn't we take the console
> sempahore when doing cursor ops in the workqueue ?

I believe so.  I'm not sure where to start though. info->fb_cursor is called 
by at least two functons (fbcon_cursor, fb_flash_cursor), and I don't see any 
form of locking, especially for the data in info->cursor which is constantly 
being modified by one and read by another.

>
> In my tree, I have moved the VT blanking code out of the timer to a
> workqueue as well and fixed other VT stuffs to make sure we always
> have the console semaphore when getting to fbdev's. The current
> "lock-less" state of the whole thing is scary...
>

Yes :-(.

> > 6. [RIVAFB]:
> >
> > 	a. Implemented I2C/DDC2 support.  Changing video modes should be more
> > robust even when using stty.
>
> I strongly suggest that you look at what I've done for radeonfb and stty
> in my tree with FB_ACTIVATE_FIND and my mode search algorithm....

Ok. 

>
> > 	b. fixed various hardware cursor corruption
> > 	c. fixed maximum yres_virtual.  Hardware accel engine will crash if blit
> > rectangle dimensions/origin exceeds 0x7fff.
> > 	d. added new boot parameter, "strictmode", to force driver to use only
> > modes specified in the EDID block.
>
> Boot parameters are evil... we should default to the "right" way whenever
> possible. Let's make sure we properly deal with either complete modes

Evil, yes, but for now, necessary. Until the stty fix (and the 
FB_ACTIVATE_FIND) is accepted by James, I will need this new boot parameter. 
 
I'll submit a new patch (without the fbi2c code) by next week.  Still too busy 
to work full time with fbdev.

Tony


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