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

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

On Thu, 20 Jun 2024, "Golani, Mitulkumar Ajitkumar" <mitulkumar.ajitkumar.golani@intel.com> wrote:
> Hi @Nathan Chancellor,
>
> Yes, with do_div, we are expecting the remainder value. Regarding the
> warning related to the adjusted_pixel_rate type cast, I haven't been
> able to reproduce this locally, possibly due to differences in the
> cross-compiler. We should consider typecasting adjusted_pixel_rate or
> treating it as unsigned ?

Please avoid top-posting on the mailing lists.

I'm guessing this will be enough.

diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index 6430da25957d..5a0da64c7db3 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -137,7 +137,7 @@ 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;
+	u64 adjusted_pixel_rate;
 	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
 
 	desired_refresh_rate = drm_mode_vrefresh(adjusted_mode);


BR,
Jani.

>
> Adding @Nikula, Jani to suggest.
>
> Regards,
> Mitul
>> -----Original Message-----
>> From: Nathan Chancellor <nathan@kernel.org>
>> Sent: Wednesday, June 19, 2024 11:56 PM
>> To: Golani, Mitulkumar Ajitkumar <mitulkumar.ajitkumar.golani@intel.com>
>> Cc: intel-gfx@lists.freedesktop.org; Nautiyal, Ankit K
>> <ankit.k.nautiyal@intel.com>; intel-xe@lists.freedesktop.org
>> Subject: Re: [PATCH v16 9/9] drm/i915: Compute CMRR and calculate vtotal
>>
>> 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@kernel.org>
>> > > Sent: Wednesday, June 19, 2024 9:12 PM
>> > > To: Golani, Mitulkumar Ajitkumar
>> > > <mitulkumar.ajitkumar.golani@intel.com>
>> > > Cc: intel-gfx@lists.freedesktop.org; Nautiyal, Ankit K
>> > > <ankit.k.nautiyal@intel.com>; intel-xe@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

-- 
Jani Nikula, Intel