[Intel-gfx] [PATCH 8/9] drm/i915/gtt: Make swapping the pd entry generic

[Chris Wilson]

Quoting Mika Kuoppala (2019-06-11 18:27:30)
> Swapping a pd entry is same across the page directories, if
> we succeed we need to increment the count and write the phys page
> entry. Make a common function for it.
> 
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 41 +++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index f1d7874834e2..9b0d0a077e31 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -752,6 +752,27 @@ static void __set_pd_entry(struct i915_page_directory * const pd,
>                        gen8_pde_encode(px_dma(to), I915_CACHE_LLC));    \
>  })
>  
> +static void *__swap_pd_entry(struct i915_page_directory * const pd,
> +                            const unsigned short pde,
> +                            void * const old_val,
> +                            void * const new_val,
> +                            const u64 encoded_entry)

Mark this as inline and pass in the encode function, the compiler should
do the rest.

> +{
> +       void * const old = cmpxchg(&pd->entry[pde], old_val, new_val);
> +
> +       if (likely(old == old_val)) {
> +               atomic_inc(&pd->used);

Hmm, looking at this again, this would be safer if atomic_inc was before
the cmpxchg, with an atomic_dec on the fail path.

> +               if (likely(pd_has_phys_page(pd)))
> +                       __set_pd_entry(pd, pde, encoded_entry);
> +       }
> +
> +       return old;
> +}
-Chris