[Intel-gfx] [PATCH 1/5] drm/i915: Fix forcewake counts for gen8

[Ben Widawsky]

On Fri, Feb 21, 2014 at 05:31:59PM +0200, mika.kuoppala at intel.com wrote:
> From: Mika Kuoppala <mika.kuoppala at intel.com>
> 
> 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 at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> Reviewed-by: Ben Widawsky <ben at bwidawsk.net>

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.

[snip]


-- 
Ben Widawsky, Intel Open Source Technology Center