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SubjectRe: [PATCH 1/5] Backlight: Add backlight type
On Fri, Nov 19, 2010 at 12:05:23PM -0800, Andrew Morton wrote:
> On Fri, 19 Nov 2010 10:53:52 -0500
> Matthew Garrett <mjg@redhat.com> wrote:
>
> > There may be multiple ways of controlling the backlight on a given machine.
> > Allow drivers to expose the type of interface they are providing, making
> > it possible for userspace to make appropriate policy decisions.
> >
> > ...
> >
> > 60 files changed, 102 insertions(+), 0 deletions(-)
>
> This patch has a pretty short half-life.

Well, ideally it would have landed in the backlight tree when I sent it
months ago. Then we'd have the opportunity to ensure that everything was
fixed up before it went in in the merge window.

> > @@ -62,6 +68,8 @@ struct backlight_properties {
> > /* FB Blanking active? (values as for power) */
> > /* Due to be removed, please use (state & BL_CORE_FBBLANK) */
> > int fb_blank;
> > + /* Backlight type */
> > + enum backlight_type type;
> > /* Flags used to signal drivers of state changes */
> > /* Upper 4 bits are reserved for driver internal use */
> > unsigned int state;
>
> And if/when the half-life expires, we'll have drivers in-tree which
> forget to set backlight_properties.type. I haven't checked, but if
> we're lucky they will default to "0".

Depends entirely on whether they kzalloc the structure or not before
calling backlight_device_register().

> What will be the runtime effects upon such unconverted drivers?
> Ideally we'd like them to continue to work OK, and to emit a runtime
> warning. In which case you'll need BACKLIGHT_RAW=1 so the unconverted
> driver can be detected, warned about and fixed up by the core code.

The worst case I can think of is that we walk off the array - I guess
there's an argument for sanity checking that in backlight_show_type().

--
Matthew Garrett | mjg59@srcf.ucam.org


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