Re: [Intel-gfx] [PATCH v2] drm/i915/hwmon: Fix a build error used with clang compiler

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Sun, 30 Oct 2022 23:37:59 -0700, Gwan-gyeong Mun wrote:
>

Hi GG,

> On 10/31/22 7:19 AM, Dixit, Ashutosh wrote:
> > On Fri, 28 Oct 2022 21:42:30 -0700, Gwan-gyeong Mun wrote:
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
> >> index 9e9781493025..c588a17f97e9 100644
> >> --- a/drivers/gpu/drm/i915/i915_hwmon.c
> >> +++ b/drivers/gpu/drm/i915/i915_hwmon.c
> >> @@ -101,21 +101,16 @@ hwm_field_read_and_scale(struct hwm_drvdata *ddat, i915_reg_t rgadr,
> >>
> >>   static void
> >>   hwm_field_scale_and_write(struct hwm_drvdata *ddat, i915_reg_t rgadr,
> >> -			  u32 field_msk, int nshift,
> >> -			  unsigned int scale_factor, long lval)
> >> +			  int nshift, unsigned int scale_factor, long lval)
> >>   {
> >>	u32 nval;
> >> -	u32 bits_to_clear;
> >> -	u32 bits_to_set;
> >>
> >>	/* Computation in 64-bits to avoid overflow. Round to nearest. */
> >>	nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor);
> >>
> >> -	bits_to_clear = field_msk;
> >> -	bits_to_set = FIELD_PREP(field_msk, nval);
> >> -
> >>	hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr,
> >> -					    bits_to_clear, bits_to_set);
> >> +					    PKG_PWR_LIM_1,
> >> +					    REG_FIELD_PREP(PKG_PWR_LIM_1, nval));
> >
> > I registered my objection to this patch already here:
> >
> > https://lore.kernel.org/intel-gfx/87ilk7pwrw.wl-ashutosh.dixit@intel.com/
> >
> > the crux of which is "hwm_field_scale_and_write() pairs with
> > hwm_field_read_and_scale() (they are basically a set/get pair) so it is
> > desirable they have identical arguments. This patch breaks that symmetry".
> >
> > We can merge this patch now but the moment a second caller of
> > hwm_field_scale_and_write arrives this patch will need to be reverted.
> >
> > I have also posted my preferred way (as I previously indiecated) of fixing
> > this issue here (if this needs to be fixed in i915):
> >
> > https://patchwork.freedesktop.org/series/110301/
> >
> The given link (https://patchwork.freedesktop.org/series/110301/) is an
> inline function that reduces the checks of REG_FIELD_PREP() and pursues the
> same functionality.
> It's not a good idea to add and use duplicate new inline functions with
> reduced functionality under different names.

See if you like v2 better :-)

> +/* FIELD_PREP and REG_FIELD_PREP require a compile time constant mask */
> +static u32 hwm_field_prep(u32 mask, u32 val)
> +{
> +	return (val << __bf_shf(mask)) & mask;
> +}
> +
>  static void
>  hwm_locked_with_pm_intel_uncore_rmw(struct hwm_drvdata *ddat,
>				    i915_reg_t reg, u32 clear, u32 set)
> @@ -112,7 +118,7 @@  hwm_field_scale_and_write(struct hwm_drvdata *ddat,
> i915_reg_t rgadr,
>	nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor);
>
>	bits_to_clear = field_msk;
> -	bits_to_set = FIELD_PREP(field_msk, nval);
> +	bits_to_set = hwm_field_prep(field_msk, nval);
>
>	hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr,
>					    bits_to_clear, bits_to_set);
>
>
> The patch
> (https://patchwork.freedesktop.org/patch/509248/?series=110094&rev=5) that
> fixed the build error in a simplified form was added as there is only one
> place that calls the hwm_field_scale_and_write() function at this time.
>
> If more places that use the hwm_field_scale_and_write() function are added
> in the future, how about changing the interface that calls this function as
> Jani previously suggested?

Sorry, which interface change which Jani suggested are you referring to? I
don't recall seeing anything but maybe I am mistaken.

Thanks.
--
Ashutosh

> > IMO it would be a mistake to use REG_FIELD_PREP or FIELD_PREP here since
> > here the mask comes in as a function argument whereas REG_FIELD_PREP and
> > FIELD_PREP require that mask to be a compile time constant.