[Ksummit-2010-discuss] [v2] Remaining BKL users, what to do
hidave.darkstar at gmail.com
Tue Oct 19 21:43:21 PDT 2010
On Wed, Oct 20, 2010 at 4:44 AM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Tuesday 19 October 2010 22:29:12 Greg KH wrote:
>> On Tue, Oct 19, 2010 at 09:40:47PM +0200, Oliver Neukum wrote:
>> > Am Dienstag, 19. Oktober 2010, 21:37:35 schrieb Greg KH:
>> > > > So no need to clean it up for multiprocessor support.
>> > > >
>> > > > http://download.intel.com/design/chipsets/datashts/29067602.pdf
>> > > > http://www.intel.com/design/chipsets/specupdt/29069403.pdf
>> > >
>> > > Great, we can just drop all calls to lock_kernel() and the like in the
>> > > driver and be done with it, right?
>> > No,
>> > you still need to switch off preemption.
>> Hm, how would you do that from within a driver?
> I think this would do:
> drm/i810: remove SMP support and BKL
> The i810 and i815 chipsets supported by the i810 drm driver were not
> officially designed for SMP operation, so the big kernel lock is
> only required for kernel preemption. This disables the driver if
> preemption is enabled and removes all calls to lock_kernel in it.
> If you own an Acorp 6A815EPD mainboard with a i815 chipset and
> two Pentium-III sockets, and want to run recent kernels on it,
> tell me about it.
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index b755301..e071bc8 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -73,8 +73,8 @@ source "drivers/gpu/drm/radeon/Kconfig"
> config DRM_I810
> tristate "Intel I810"
> - # BKL usage in order to avoid AB-BA deadlocks, may become BROKEN_ON_SMP
> - depends on DRM && AGP && AGP_INTEL && BKL
> + # PREEMPT requires BKL support here, which was removed
> + depends on DRM && AGP && AGP_INTEL && !PREEMPT
be curious, why can't just fix the lock_kernel logic of i810? Fixing
is too hard?
Find a i810 hardware should be possible, even if the hardware does not
support SMP, can't we test the fix with preemption?
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