Re: [PATCH 1/9] drm/i915/dsb: Replace HAS_DSB check with dsb->cmd_buf check

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On 31-01-2020 17:12, Ville Syrjälä wrote:
On Fri, Jan 31, 2020 at 03:04:17PM +0530, Manna, Animesh wrote:
On 30-01-2020 23:43, Souza, Jose wrote:
On Wed, 2020-01-29 at 20:20 +0200, Ville Syrjala wrote:
From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>

We may want to not use the DSB even if the platform has one.
So replace the HAS_DSB check in the _put() with a cmd_buf check
that will work in either case.
Reviewed-by: José Roberto de Souza <jose.souza@xxxxxxxxx>

Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
   drivers/gpu/drm/i915/display/intel_dsb.c | 3 +--
   1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
b/drivers/gpu/drm/i915/display/intel_dsb.c
index 9dd18144a664..12776f09f227 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -160,9 +160,8 @@ intel_dsb_get(struct intel_crtc *crtc)
   void intel_dsb_put(struct intel_dsb *dsb)
   {
   	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc),
dsb);
-	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
- if (!HAS_DSB(i915))
+	if (!dsb->cmd_buf)
Ville and Jose,

Have a concern here. In intel_dsb_get() if get failure during i915_gem_object_create_internal, i915_gem_object_ggtt_pin, i915_gem_object_pin_map then we may not have dsb->cmd_buf.
Then ref-count mechanism will break.
Hmm. Yeah. The refcount WARN could easily be fixed by either
decrementung refcount on get() fail or doing the "let's never use
DSB" patch after the refcount inc.

Hmm, from design point get/put/ref-count mechanism introduced to check dsp-api are used properly or not.
For erroneous case managing ref-count in get() itself void the purpose of put() call.
For example,

intel_dsb_get()
got error from i915_gem_object_create_internal, i915_gem_object_ggtt_pin, i915_gem_object_pin_map
intel_dsb_put
intel_dsb_put
...

Should throw warning but can not if we manage in get() itself.

Regards,
Animesh


I feel HAS_DSB(i915) check is better than dsb->cmd_buf otherwise need to do some cleanup is intel_dsb_get() as well.

Regards,
Animesh

   		return;
if (WARN_ON(dsb->refcount == 0))
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