On Mon, Feb 24, 2014 at 01:27:09PM +0200, Ville Syrjälä wrote: > On Fri, Feb 21, 2014 at 11:38:48AM -0800, Ben Widawsky wrote: > > On Fri, Feb 21, 2014 at 05:31:59PM +0200, mika.kuoppala@xxxxxxxxx wrote: > > > From: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > > > > > > Sometimes generic driver code gets forcewake explicitly by > > > gen6_gt_force_wake_get(), which check forcewake_count before accessing > > > hardware. However the register access with gen8_write function access > > > low level hw accessors directly, ignoring the forcewake_count. This > > > leads to nested forcewake get from hardware, in ring init and possibly > > > elsewhere, causing forcewake ack clear errors and/or hangs. > > > > > > Fix this by checking the forcewake count also in gen8_write > > > > > > v2: Read side doesn't care about shadowed registers, > > > Remove __needs_put funkiness from gen8_write. (Ville) > > > Improved commit message. > > > > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=74007 > > > Cc: Ben Widawsky <benjamin.widawsky@xxxxxxxxx> > > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > > > Reviewed-by: Ben Widawsky <ben@xxxxxxxxxxxx> > > > > For those concerned with the performance implication of the extra if > > (if anyone at all cares, it's Chris) - I suppose we could also just add > > the lock to gen6_gt_force_wake_get/put. > > Two things: > a) I don't understand what you mean here. uncore.lock already protects > the forcewake count in gen6_gt_force_wake_get/put. Also there's no way > to avoid the branch here since doing a .force_wake_put() w/o checking > the forcewake count is never ok. > I meant acquire the lock in get() release the lock in put() > b) The cost of branch should be a drop in the ocean compared to the > cost of the register reads/writes in .forcewake_get/put. > > -- > Ville Syrjälä > Intel OTC -- Ben Widawsky, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
