Re: [PATCH] drm/amd/display: add parameter backlight_min

[Filip Moc <dev@moc6.cz>]

Hello Harry,

thank you for your response.

> amdgpu.backlight_min=2:-1

almost :-)

Array elements in module parameters are separated by commas not colons.
So for cmdline it should look like this:
amdgpu.backlight_min=2,-1

Though you can just drop the ,-1 relying on kernel leaving the rest of array
untouched. Which I would recommend as there is no point for user to
follow AMDGPU_DM_MAX_NUM_EDP.
Only when you need to override some other display than display 0 then you may
need to use -1. E.g. backlight_min=-1,2 overrides display 1 to min backlight=2
while keeping display 0 with no override.

When amdgpu is loaded as a kernel module, backlight_min can also be passed as a
parameter to modprobe, e.g.:
modprobe backlight_min=2
So in that case you probably want to add something like
options amdgpu backlight_min=2 to /etc/modprobe.d/amdgpu.conf
(and also run update-initramfs if amdgpu is loaded by initramfs).

I'll add some examples to commit message in v2.

Filip


V Mon, Oct 31, 2022 at 10:24:25AM -0400, Harry Wentland napsal(a):
> On 2022-10-29 15:13, Filip Moc wrote:
> > There are some devices on which amdgpu won't allow user to set brightness
> > to sufficiently low values even though the hardware would support it just
> > fine.
> > 
> > This usually happens in two cases when either configuration of brightness
> > levels via ACPI/ATIF is not available and amdgpu falls back to defaults
> > (currently 12 for minimum level) which may be too high for some devices or
> > even the configuration via ATIF is available but the minimum brightness
> > level provided by the manufacturer is set to unreasonably high value.
> > 
> > In either case user can use this new module parameter to adjust the
> > minimum allowed backlight brightness level.
> > 
> 
> Thanks for this patch and covering all the bases.
> 
> It might be useful to have an example in the commit description on
> how to set the array property. I assume it looks like this if I
> wanted to set the first device to a minimum of 2 and leave the default
> for the 2nd one:
> 
> amdgpu.backlight_min=2:-1
> 
> Either way, this patch is
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> 
> Harry
> 
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=203439>> 
> > Signed-off-by: Filip Moc <dev@moc6.cz>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu.h               |  3 +++
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c           | 15 +++++++++++++++
> >  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 15 +++++++++++++++
> >  3 files changed, 33 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > index 0e6ddf05c23c..c5445402c49d 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > @@ -200,6 +200,9 @@ extern uint amdgpu_dc_debug_mask;
> >  extern uint amdgpu_dc_visual_confirm;
> >  extern uint amdgpu_dm_abm_level;
> >  extern int amdgpu_backlight;
> > +#ifdef CONFIG_DRM_AMD_DC
> > +extern int amdgpu_backlight_override_min[];
> > +#endif
> >  extern struct amdgpu_mgpu_info mgpu_info;
> >  extern int amdgpu_ras_enable;
> >  extern uint amdgpu_ras_mask;
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > index 16f6a313335e..f2fb549ac52f 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > @@ -43,6 +43,7 @@
> >  #include "amdgpu_irq.h"
> >  #include "amdgpu_dma_buf.h"
> >  #include "amdgpu_sched.h"
> > +#include "amdgpu_dm.h"
> >  #include "amdgpu_fdinfo.h"
> >  #include "amdgpu_amdkfd.h"
> >  
> > @@ -853,6 +854,20 @@ int amdgpu_backlight = -1;
> >  MODULE_PARM_DESC(backlight, "Backlight control (0 = pwm, 1 = aux, -1 auto (default))");
> >  module_param_named(backlight, amdgpu_backlight, bint, 0444);
> >  
> > +/**
> > + * DOC: backlight_min (array of int)
> > + * Override minimum allowed backlight brightness signal (per display).
> > + * Must be less than the maximum brightness signal.
> > + * Negative value means no override.
> > + *
> > + * Defaults to all -1 (no override on any display).
> > + */
> > +#ifdef CONFIG_DRM_AMD_DC
> > +int amdgpu_backlight_override_min[AMDGPU_DM_MAX_NUM_EDP] = {[0 ... (AMDGPU_DM_MAX_NUM_EDP-1)] = -1};
> > +MODULE_PARM_DESC(backlight_min, "Override minimum backlight brightness signal (0..max-1, -1 = no override (default))");
> > +module_param_array_named(backlight_min, amdgpu_backlight_override_min, int, NULL, 0444);
> > +#endif
> > +
> >  /**
> >   * DOC: tmz (int)
> >   * Trusted Memory Zone (TMZ) is a method to protect data being written
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > index eb4ce7216104..e2c36ba93d05 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -3911,6 +3911,21 @@ static void amdgpu_dm_update_backlight_caps(struct amdgpu_display_manager *dm,
> >  	dm->backlight_caps[bl_idx].min_input_signal = AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
> >  	dm->backlight_caps[bl_idx].max_input_signal = AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
> >  #endif
> > +
> > +	if (amdgpu_backlight_override_min[bl_idx] >= 0) {
> > +		if (amdgpu_backlight_override_min[bl_idx] < dm->backlight_caps[bl_idx].max_input_signal) {
> > +			DRM_INFO("amdgpu: backlight[%i]: overriding minimum brightness from %i to %i\n",
> > +				  bl_idx,
> > +				  dm->backlight_caps[bl_idx].min_input_signal,
> > +				  amdgpu_backlight_override_min[bl_idx]);
> > +			dm->backlight_caps[bl_idx].min_input_signal = amdgpu_backlight_override_min[bl_idx];
> > +		} else {
> > +			DRM_ERROR("amdgpu: backlight[%i]: minimum brightness override (%i) is not below maximum (%i)\n",
> > +				  bl_idx,
> > +				  amdgpu_backlight_override_min[bl_idx],
> > +				  dm->backlight_caps[bl_idx].max_input_signal);
> > +		}
> > +	}
> >  }
> >  
> >  static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
> > 
> > base-commit: d8c03bfe146fd5e081a252cd34f3f12ca0255357
>