Re: [PATCH 08/11] drm/i915/dsb: Add i915.enable_dsb module parameter

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 19 Jun 2024, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Tue, Jun 18, 2024 at 02:07:56PM +0300, Jani Nikula wrote:
>> On Tue, 11 Jun 2024, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
>> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> >
>> > As we extend the use of DSB for critical pipe/plane register
>> > programming, it'll be nice to have an escape valve at hand,
>> > in case things go very poorly. To that end, add a i915.enable_dsb
>> > modparam by which we can force the driver to take the pure mmio
>> > path instead.
>> >
>> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/display/intel_display_params.c | 3 +++
>> >  drivers/gpu/drm/i915/display/intel_display_params.h | 1 +
>> >  drivers/gpu/drm/i915/display/intel_dsb.c            | 3 +++
>> >  3 files changed, 7 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c b/drivers/gpu/drm/i915/display/intel_display_params.c
>> > index aebdb7b59dbf..449a31767791 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_display_params.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_display_params.c
>> > @@ -54,6 +54,9 @@ intel_display_param_named_unsafe(enable_dc, int, 0400,
>> >  intel_display_param_named_unsafe(enable_dpt, bool, 0400,
>> >  	"Enable display page table (DPT) (default: true)");
>> >  
>> > +intel_display_param_named_unsafe(enable_dsb, bool, 0600,
>> > +	"Enable display state buffer (DSB) (default: true)");
>> 
>> Not much point in leaving the module param 0600, is there?
>
> It'll let you try both dsb and mmio paths at runtime without
> having to do a full reboot/reload.

I mean does any code actually look at the *module* parameter runtime?
It's only the initial value for the device param?

BR,
Jani.

>
>> 
>> BR,
>> Jani.
>> 
>> > +
>> >  intel_display_param_named_unsafe(enable_sagv, bool, 0400,
>> >  	"Enable system agent voltage/frequency scaling (SAGV) (default: true)");
>> >  
>> > diff --git a/drivers/gpu/drm/i915/display/intel_display_params.h b/drivers/gpu/drm/i915/display/intel_display_params.h
>> > index 1208a62c16d2..48c29c55c939 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_display_params.h
>> > +++ b/drivers/gpu/drm/i915/display/intel_display_params.h
>> > @@ -31,6 +31,7 @@ struct drm_i915_private;
>> >  	param(int, vbt_sdvo_panel_type, -1, 0400) \
>> >  	param(int, enable_dc, -1, 0400) \
>> >  	param(bool, enable_dpt, true, 0400) \
>> > +	param(bool, enable_dsb, true, 0600) \
>> >  	param(bool, enable_sagv, true, 0600) \
>> >  	param(int, disable_power_well, -1, 0400) \
>> >  	param(bool, enable_ips, true, 0600) \
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
>> > index bee48ac419ce..2ab3765f6c06 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dsb.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
>> > @@ -460,6 +460,9 @@ struct intel_dsb *intel_dsb_prepare(struct intel_atomic_state *state,
>> >  	if (!HAS_DSB(i915))
>> >  		return NULL;
>> >  
>> > +	if (!i915->display.params.enable_dsb)
>> > +		return NULL;
>> > +
>> >  	/* TODO: DSB is broken in Xe KMD, so disabling it until fixed */
>> >  	if (!IS_ENABLED(I915))
>> >  		return NULL;
>> 
>> -- 
>> Jani Nikula, Intel

-- 
Jani Nikula, Intel