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    SubjectRe: hung bootup with "drm/radeon/kms: move radeon KMS on/off switch out of staging."

    * Alex Deucher <alexdeucher@gmail.com> wrote:

    > On Thu, Feb 4, 2010 at 1:12 PM, Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > > * Matthew Garrett <mjg59@srcf.ucam.org> wrote:
    > >
    > >> On Thu, Feb 04, 2010 at 06:54:45PM +0100, Ingo Molnar wrote:
    > >>
    > >> > But you could claim that it's not a regression because 1) technically the
    > >> > code got introduced in drivers/staging/, and staging drivers are not on
    > >> > the regression list 2) the Kconfig value is default-off so it can only
    > >> > harm those who got lured by a new Kconfig value popping up in -rc7 in a
    > >> > well working driver they already have enabled.
    > >> >
    > >> > So the moving of driver functionality from drivers/staging/ to drivers/
    > >> > is a grey area it appears. Wouldnt it have been better to do this in the
    > >> > next merge window, as all other drivers do? It's not new hardware
    > >> > enablement either, it's feature enablement for an existing driver.
    > >>
    > >> The reason the option was in staging (as has been mentioned before) was
    > >> because the ABI wasn't felt to be stable enough. Upstream is now willing to
    > >> commit to that stability, so now seems as good a time to move it as any.
    > >> There's no code change and there's no default configuration change, so I
    > >> really can't see any way that it can be classed as a regression.
    > >
    > > But that argument in essence renders the regression policy meaningless for
    > > such code: just about any new driver feature under the sun could be shaped as
    > > a Kconfig option, introduced via a drivers/staging Kconfig entry, and then
    > > activated via a twoliner commit in a later -rc.
    > >
    > > IMHO the point of tracking regressions is to reduce the bugginess of the
    > > kernel and thus to help users, not to give ground for legalistic arguments.
    > >
    > > There _are_ common-sense exceptions from the regression rules, such as the
    > > introduction of a new piece of hardware that was previously unsupported
    > > (hence there's no expectation of stability) - but the tweaking of an
    > > existing, widely used driver (even if the new opion is default-off) hardly
    > > seems to qualify for that.
    > >
    >
    > This is a completely new driver. It's only part of the existing drm for
    > compatibility reasons. It requires an entirely different graphics stack
    > above it and works very differently from the old drm stack.

    Will the user know? IMHO what matters in the end is user expectation.

    Lets walk through what a current kernel tester of the drm/radeon driver sees
    when he types 'make oldconfig' after installing the (to-be-released) .33-rc7
    kernel. Firstly, the user with a brand-new distro already has this enabled:

    CONFIG_DRM_RADEON=y

    and knows the driver, and it performs adequately. Then in -rc7 he gets a new
    option:

    ATI Radeon (DRM_RADEON) [Y/n/?] y
    Enable modesetting on radeon by default (DRM_RADEON_KMS) [N/y/?] (NEW)

    The user might easily go: "Hey this is a driver i already have, and there's a
    new sub-option for this well-working driver. Sure, enable it, these kernel
    folks know what they are doing and i rarely see any crashes past -rc2
    kernels."

    Does this new option tell him what you just told me, that:

    > This is a completely new driver. It's only part of the existing drm for
    > compatibility reasons. It requires an entirely different graphics stack
    > above it and works very differently from the old drm stack.

    ?

    it doesnt. Even if he types '?', it tells:

    CONFIG_DRM_RADEON_KMS:

    Choose this option if you want kernel modesetting enabled by default,
    and you have a new enough userspace to support this. Running old
    userspaces with this enabled will cause pain.

    The user will likely go "cool I have a fresh distro with recent Xorg, lets
    try it".

    If this is really a brand new driver essentially fresh out of
    drivers/staging/ in -rc7 you should be abundantly clear about that in the
    Kconfig help text - that it's a brand new driver and that it might crash on
    bootup, etc.

    Thanks,

    Ingo



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