Re: [Linux-fbdev-devel] Some questions

[Thomas W. <th...@wi...>]

Antonino Daplas wrote:
>>Can anybody confirm that this (ie both low level driver and fbcon in
>>kernel) is supposed to work in 2.5.63 (making it a bug in my sisfb
>>implementation)? Did I perhaps miss anything, like a kernel parameter to
>>activate fbcon or similar?
> 
> Yes, it it does work.

OK, now it works here, too. Seems my debug-printks during initialisation 
made the kernel go bananas. As soon as I removed them, it walks along...

But I noticed another issue here:

When switching to gfx mode during boot (ie as soon as the penguin 
appears), the text console is aligned correctly at all edges, with all 
lines visible.

But when "initial console" starts, the mode is again changed, and now 
the last line of text is nearly invisible, its upper half appears at the 
lower screen edge, the lower half is below the screen's edge. The space 
between the penguin and the text is notably thicker.

This can be recovered by switching to another VT and back. This makes 
the penguin disappear, and restores the console dimensions/edges to normal.

Interestingly, this only happens with 800x600; this mode is chosen upon 
requesting 800x592 (because of the font size). At 1024x768, everything 
is as it should.

>>However, I could not manage to gain a graphical console if sisfb is a
>>module, but fbcon is in the kernel. Is this combination supposed to
>>work? If so, how?
> 
> No, fbcon will not load unless there's at least one registered fbdev.
> So, you must compile sisfb statically too.

Then this should definitely go into the kernel config rules, I guess :)

>>a) Calculating the desired mode resolution my simply multiplying the
>>rows/cols by the font size very often results in odd modes like 800x592.
>>This even when using a standard 8x16 font, not thinking of situations
>>where for instance 12x22 fonts are used. How is the low level driver
>>supposed to handle this?
> 
> Ideally, the driver should round up to the nearest mode it's capable
> of.  The "fraction of a character dimensions" will be automatically
> cleared by the "clear_margins" hook.

OK, that's exactly what I do now. I currently tend to the assumption 
that this mode should be larger than the requested one...?

>>To temporarily overcome this, I implemented a somewhat fuzzy mode
>>identification routine, searching for modes with resolutions within a
>>range of [desired res] - [desired res + 16]. But I can't imagine this
>>being the Real Thing.
> 
> Yes, that's the Real Thing :-)  fbcon_resize has a "fuzzy mode" too --
> it won't do an fb_set_var() if the change in dimensions is only a
> fraction of a character's dimension.

Ack. Is 16 fuzzy enough, what do you think?

> Right, using stty to change the window size assumes that the fbdev
> driver has an algorithm to calculate modelines based on xres and yres
> independently.  This is probably a bit of work for most driver authors.

Well, not as much work as more a lack of definition. If the user 
specified a default of 800x600-75 I can't simply assume he also wants 
1024x768-75.

> There's new code in fbmon.c (fb_find_mode and fb_validate_mode) that
> should ease code writing if you have a VESA GTF compliant monitor.  You
> can use that if you want as long as the display's operating limits are
> known (info->monspecs).

Well, this assumes that the user always want the best refresh rate, 
which is not desired in all cases.

> Another solution is to reimplement resizing by fbset.  The code is not
> very difficult and can be added if most people want it.

Awaiting public demand :)

> Yes, this is a limitation of stty.  It calls con_resize twice (one for
> row and another for cols, depending on the order of the options) so it
> will not work if the driver only supports a fixed set of modes.  Another
> reason to bring back fbset resizing.

Think so, too. That's a really stupid behavior otherwise, since it 
involves two mode changes, with one really undesired mode on the way.

> Scrolling mode is now determined by fbcon.  If var->accel_flag is
> nonzero, scrolling is ypan, otherwise, it's yredraw.  It's because ypan
> requres a lot of block copy which is slow when done by software.
> 
> I still believe though that scrolling should be determined by the
> driver, not fbcon.

Well, what should I do now?

The rivafb only forces y panning (ie sets yres_virtual to maximum) if 
yres_virtual is -1. This is never the case, as default var is constantly 
reused and I nowhere saw that any of the res_virtuals was set to -1.

Thomas

-- 
Thomas Winischhofer
Vienna/Austria
mailto:th...@wi...            http://www.winischhofer.net/