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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jun 19, 2024 at 04:11:08PM +0300, Jani Nikula wrote:
> 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?

You can change it via the debugfs i915_params/* thing.

-- 
Ville Syrjälä
Intel