>> A better idea is to split user/priviledge command into register bank
>> in different 4k page boundary. That's cost nothing in hardware.
>
> Furthermore, there may not be anything to split.  I propose the
> following:
>
>   - An unprivileged task can only submit commands via indirect DMA.
>     Each indirect DMA buffer is submitted by ioctling the kernel
>

You can't do that. It could means : software filtering that is slow,
and/or kernel system call that is also slow.

Why do you need that ? If you provided hardware access to a safe interface
of the card, there is no problem. (this interface context should be saved
and restored by the kernel when a task switch occur, the card could also
manage "few" context (3/4, the opengl programme and the windows manager at
least))

>   - PIO is only available to privileged tasks, normally only the kernel
>     driver.

Ok, that could be used for windows clipping, if avalable, managing
contexte, managing the mouse cursor.

> Clean and simple.
>
> Regards,
>
> Daniel
>


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