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    SubjectRe: Proposal for a low-level Linux display framework
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    On Sat, Sep 17, 2011 at 3:06 PM, Florian Tobias Schandinat
    <FlorianSchandinat@gmx.de> wrote:
    > On 09/17/2011 06:23 PM, Dave Airlie wrote:
    >>>
    >>> Is it? Well, okay, I don't want to use any acceleration that can crash my
    >>> machine, where can I select it, preferably as compile time option? I didn't find
    >>> such a thing for Intel or Radeon. Don't say, I should rely on userspace here or
    >>> use fbdev for this.
    >>
    >> Just tell the X driver to not use acceleration, and it you won't get
    >> any acceleration used, then you get complete stability. If a driver
    >> writer wants to turn off all accel in the kernel driver, it can, its
    >> not an option we've bothered with for intel or radeon since it really
    >> makes no sense. To put it simply you don't really seem to understand
    >> the driver model around KMS. If no userspace app uses acceleration
    >> then no acceleration features will magically happen. If you want to
    >> write a simple app against the KMS API like plymouth you can now use
    >> the dumb ioctls to create and map a buffer that can be made into a
    >> framebuffer. Also you get hw cursors + modesetting.
    >
    > Again, you seem to not understand my reasoning. The "if" is the problem, it's
    > the kernels job to ensure stability. Allowing the userspace to decide whether it
    > crashes my machine is not acceptable to me.
    > I do not claim that it is impossible to write a KMS driver in a way that it does
    > not crash, but it seems more difficult than writing an fbdev driver.
    >

    It's perfectly valid to write a KMS DRM driver that doesn't support
    acceleration in which case it will be just as "stable" as a fbdev
    driver. In fact on modern hardware it's probably easier to write a
    KMS DRM driver than a fbdev driver because the API and internal
    abstractions match the hardware better. If you have hardware with 4
    display controllers, 2 DACs, a TMDS encoder, and a DP encoder how do
    you decide which combination of components and modes to light up at
    boot using fbdev?

    Alternatively, if you wanted to support acceleration as well, you can
    add a module option to force acceleration off at the kernel level
    rather than from userspace. It's trivial.

    Alex


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