Subject: Re: RFC: framebuffer device support in NetBSD
To: None <,>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-kern
Date: 09/13/2002 22:17:03
>> Does wscons allow user space processes to access video memory?
> Sure.

Really?  I thought much of the ugliness was because on some peecee
video hardware, you _can't_ access all of video memory at once - you
have to do something akin to bank-switching.  Unless I'm completely
wrong about this, it means either exposing that ugliness to userland or
paying the penalty of a trap to the kernel whenever you access
something not currently switched in (so that the kernel can switch
things around to provide the illusion of ordinary video RAM).

Which would in turn mean that, while yes, wscons does allow user
processes to access video memory, it doesn't (can't) present any sort
of uniform hardware-independent view.  You'd have to provide an
interface that exposes the bank-switching nastiness, and to properly
encapsulate all the ugliness in the driver where it belongs, you'd have
to _at least_ cross into the kernel to switch banks.

/~\ The ASCII				der Mouse
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