linux-kernel - Re: [Intel-gfx] [PATCH v11 3/4] drm/i915: Use new CRC debugfs API

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Date:   Tue, 15 Nov 2016 10:27:33 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     David Weinehall <tao@...nel.org>
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Thierry Reding <thierry.reding@...il.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [Intel-gfx] [PATCH v11 3/4] drm/i915: Use new CRC debugfs API

On Tue, 15 Nov 2016, David Weinehall <tao@...nel.org> wrote:
> On Mon, Nov 14, 2016 at 12:44:25PM +0200, Jani Nikula wrote:
>> On Thu, 06 Oct 2016, Tomeu Vizoso <tomeu.vizoso@...labora.com> wrote:
>> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> > index 23a6c7213eca..7412a05fa5d9 100644
>> > --- a/drivers/gpu/drm/i915/intel_display.c
>> > +++ b/drivers/gpu/drm/i915/intel_display.c
>> > @@ -14636,6 +14636,7 @@ static const struct drm_crtc_funcs intel_crtc_funcs = {
>> >  	.page_flip = intel_crtc_page_flip,
>> >  	.atomic_duplicate_state = intel_crtc_duplicate_state,
>> >  	.atomic_destroy_state = intel_crtc_destroy_state,
>> > +	.set_crc_source = intel_crtc_set_crc_source,
>> >  };
>> >  
>> >  /**
>> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
>> > index 737261b09110..31894b7c6517 100644
>> > --- a/drivers/gpu/drm/i915/intel_drv.h
>> > +++ b/drivers/gpu/drm/i915/intel_drv.h
>> > @@ -1844,6 +1844,14 @@ void intel_color_load_luts(struct drm_crtc_state *crtc_state);
>> >  /* intel_pipe_crc.c */
>> >  int intel_pipe_crc_create(struct drm_minor *minor);
>> >  void intel_pipe_crc_cleanup(struct drm_minor *minor);
>> > +#ifdef CONFIG_DEBUG_FS
>> > +int intel_crtc_set_crc_source(struct drm_crtc *crtc, const char *source_name,
>> > +			      size_t *values_cnt);
>> > +#else
>> > +static inline int intel_crtc_set_crc_source(struct drm_crtc *crtc,
>> > +					    const char *source_name,
>> > +					    size_t *values_cnt) { return 0; }
>> > +#endif
>> 
>> "inline" here doesn't work because it's used as a function pointer.
>> 
>> Is it better to have a function that returns 0 for .set_crc_source, or
>> to set .set_crc_source to NULL when CONFIG_DEBUG_FS=n?
>
> I'd say that whenever we have a function pointer we should have a dummy
> function without side-effects for this kind of things.

Whoever calls .set_crc_source could do smarter things depending on the
hook not being there vs. just silently plunging on.

BR,
Jani.


>
>
> Kind regards, David

-- 
Jani Nikula, Intel Open Source Technology Center