[PATCH v16 9/9] drm/i915: Compute CMRR and calculate vtotal

[Nathan Chancellor]

On Wed, Jun 19, 2024 at 06:10:34PM +0000, Golani, Mitulkumar Ajitkumar wrote:
> Hi @Nathan Chancellor
> 
> Probably fix is merged in drm-intel-next
> related patch:  https://patchwork.freedesktop.org/series/134860/
> 
> Can you please check and suggest if this patch is merged ?

This is still reproducible at commit 851de367dede ("drm/i915: Enable
plane/pipeDMC ATS fault interrupts on mtl") in drm-intel-next, which
includes that change as commit e2dc7cb72b25 ("drm/i915/display: Update
calculation to avoid overflow"). The issue is the dividend in do_div()
is required to be an unsigned 64-bit type but you used a signed type.
Updating adjusted_pixel_rate to be a u64 should resolve the issue and
match the return type of mul_u32_u32(). I just wasn't sure if that was
the only fix this code would need, as do_div() is not typically used
with an assignment.

Cheers,
Nathan

> > -----Original Message-----
> > From: Nathan Chancellor <nathan at kernel.org>
> > Sent: Wednesday, June 19, 2024 9:12 PM
> > To: Golani, Mitulkumar Ajitkumar <mitulkumar.ajitkumar.golani at intel.com>
> > Cc: intel-gfx at lists.freedesktop.org; Nautiyal, Ankit K
> > <ankit.k.nautiyal at intel.com>; intel-xe at lists.freedesktop.org
> > Subject: Re: [PATCH v16 9/9] drm/i915: Compute CMRR and calculate vtotal
> > 
> > Hi Mitul,
> > 
> > On Mon, Jun 10, 2024 at 12:52:02PM +0530, Mitul Golani wrote:
> > ...
> > > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c
> > > b/drivers/gpu/drm/i915/display/intel_vrr.c
> > > index 4ad99a54aa83..05f67dc9d98d 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> > > @@ -12,6 +12,9 @@
> > >  #include "intel_vrr_regs.h"
> > >  #include "intel_dp.h"
> > >
> > > +#define FIXED_POINT_PRECISION		100
> > > +#define CMRR_PRECISION_TOLERANCE	10
> > > +
> > >  bool intel_vrr_is_capable(struct intel_connector *connector)  {
> > >  	const struct drm_display_info *info = &connector->base.display_info;
> > > @@ -107,6 +110,52 @@ int intel_vrr_vmax_vblank_start(const struct
> > intel_crtc_state *crtc_state)
> > >  	return crtc_state->vrr.vmax -
> > > intel_vrr_vblank_exit_length(crtc_state);
> > >  }
> > >
> > > +static bool
> > > +is_cmrr_frac_required(struct intel_crtc_state *crtc_state) {
> > > +	int calculated_refresh_k, actual_refresh_k, pixel_clock_per_line;
> > > +	struct drm_display_mode *adjusted_mode = &crtc_state-
> > >hw.adjusted_mode;
> > > +	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
> > > +
> > > +	if (!HAS_CMRR(i915))
> > > +		return false;
> > > +
> > > +	actual_refresh_k =
> > > +		drm_mode_vrefresh(adjusted_mode) *
> > FIXED_POINT_PRECISION;
> > > +	pixel_clock_per_line =
> > > +		adjusted_mode->crtc_clock * 1000 / adjusted_mode-
> > >crtc_htotal;
> > > +	calculated_refresh_k =
> > > +		pixel_clock_per_line * FIXED_POINT_PRECISION /
> > > +adjusted_mode->crtc_vtotal;
> > > +
> > > +	if ((actual_refresh_k - calculated_refresh_k) <
> > CMRR_PRECISION_TOLERANCE)
> > > +		return false;
> > > +
> > > +	return true;
> > > +}
> > > +
> > > +static unsigned int
> > > +cmrr_get_vtotal(struct intel_crtc_state *crtc_state, bool
> > > +video_mode_required) {
> > > +	int multiplier_m = 1, multiplier_n = 1, vtotal, desired_refresh_rate;
> > > +	long long adjusted_pixel_rate;
> > > +	struct drm_display_mode *adjusted_mode =
> > > +&crtc_state->hw.adjusted_mode;
> > > +
> > > +	desired_refresh_rate = drm_mode_vrefresh(adjusted_mode);
> > > +
> > > +	if (video_mode_required) {
> > > +		multiplier_m = 1001;
> > > +		multiplier_n = 1000;
> > > +	}
> > > +
> > > +	crtc_state->cmrr.cmrr_n =
> > > +		desired_refresh_rate * adjusted_mode->crtc_htotal *
> > multiplier_n;
> > > +	vtotal = (adjusted_mode->crtc_clock * 1000 * multiplier_n) /
> > crtc_state->cmrr.cmrr_n;
> > > +	adjusted_pixel_rate = adjusted_mode->crtc_clock * 1000 *
> > multiplier_m;
> > > +	crtc_state->cmrr.cmrr_m = do_div(adjusted_pixel_rate,
> > > +crtc_state->cmrr.cmrr_n);
> > > +
> > > +	return vtotal;
> > > +}
> > 
> > This change is now in -next as commit 1676ecd303ac ("drm/i915: Compute
> > CMRR and calculate vtotal"), where it breaks the xe build for 32-bit platforms
> > with:
> > 
> >   $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
> > allmodconfig drivers/gpu/drm/xe/i915-display/intel_vrr.o
> >   In file included from arch/arm/include/asm/div64.h:107,
> >                    from include/linux/math.h:6,
> >                    from include/linux/kernel.h:27,
> >                    from include/linux/cpumask.h:11,
> >                    from include/linux/smp.h:13,
> >                    from include/linux/lockdep.h:14,
> >                    from include/linux/spinlock.h:63,
> >                    from include/linux/kref.h:16,
> >                    from include/drm/drm_device.h:5,
> >                    from include/drm/drm_drv.h:35,
> >                    from drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h:13,
> >                    from drivers/gpu/drm/i915/display/intel_vrr.c:7:
> >   drivers/gpu/drm/i915/display/intel_vrr.c: In function 'cmrr_get_vtotal':
> >   include/asm-generic/div64.h:222:35: error: comparison of distinct pointer
> > types lacks a cast [-Werror]
> >     222 |         (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
> >         |                                   ^~
> >   drivers/gpu/drm/i915/display/intel_vrr.c:155:35: note: in expansion of macro
> > 'do_div'
> >     155 |         crtc_state->cmrr.cmrr_m = do_div(adjusted_pixel_rate, crtc_state-
> > >cmrr.cmrr_n);
> >         |                                   ^~~~~~
> >   cc1: all warnings being treated as errors
> > 
> > Also, is do_div() correct here? It is different from the other div_() macros in that
> > the "return value" is the remainder, not the result of the division.
> > 
> > Cheers,
> > Nathan