Re: (unofficial) Debian packages for Toshiba AC100 (Tegra; armel and armhf)
Wookey <wookey@wookware.org> writes:
> +++ Luke Kenneth Casson Leighton [2011-07-25 10:13 +0100]:
>> question:
>>
>> what is the best way to actually take into account, *without*
>> requiring a total recompile of the linux kernel, *without* requiring a
>> rebuild of any debian gnu/linux packages, variations in LCD screen
>> size when the "norm" is that both the LCD and the data structures in
>> the linux kernel are typically static and non-changeable?
>
> That's a question that has bugged me for a long time too.
>
>> in some ways this is a rhetorical / leading question (but isn't
>> really) - i'm aware that there's usually an I2C ROM or other mechanism
>> for reading EDID data off of the LCD panel, to obtain its size... it's
>> just that this simply isn't done in the linux kernel source code
>> itself.
>
> And sometimes there isn't even that (SFAIK). With a direct LCD connection
> sometimes it's just a matter of what's plugged in. Ballon could have 4
> different displays 3 LCD lanels or a VGA monitor-hack (to get monitor
> signals out of the LCD connector). And I never worked out how to
> switch between displays without making a new kernel, because
> everything was clearly designed on the assumption that if the display
> was LCD then it was of a fixed type.
afaik, it's driver dependant. Some drivers (like the some kms ones) are
able to read&parse the edid to get the screen size/configuration.
You have also the possibility of having broken edid informations or no
edid informations at all, forcing to have some configuration infos in
the kernel. There are also some cases where the screen is connected
throught a controller, which is connected to the SoC, making the edid
informations wrong.
When no information available, you may use some kernel command line
argument to specify the screen type to use and rely on some list of
known configurations either stored on the driver side or in the machine
file.
These are only examples coming out of my mind, so take this with a little
grain of salt. It may be somewhat not complete/accurate.
Arnaud
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