Re: [Intel-gfx] [PATCH 04/13] drm/i915: Don't warn about zero N/P in *_calc_dpll_params()

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

On Wed, 05 Jul 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Allow *_calc_dpll_params() to be called even if the N/P dividers
> are zero without warning. We'll want to call these to make sure the
> derived values are fully computed, but not all users (VLV DSI in
> particular) don't even enable the DPLL and thus the dividers will
> be left at zero.
>
> It could also be possible that the BIOS has misprogrammed the DPLL
> (IIRC happened with some SNB machines with 4k+ displays) and thus
> we'll currently generate a lot of dmesg spew. Better be silent and
> just let the normal state checker/etc. deal with any driver bugs.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_dpll.c | 37 ++++++++++++-----------
>  1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dpll.c b/drivers/gpu/drm/i915/display/intel_dpll.c
> index 999badfe2906..71bfeea4cef2 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll.c
> @@ -314,10 +314,11 @@ int pnv_calc_dpll_params(int refclk, struct dpll *clock)
>  {
>  	clock->m = clock->m2 + 2;
>  	clock->p = clock->p1 * clock->p2;
> -	if (WARN_ON(clock->n == 0 || clock->p == 0))
> -		return 0;
> -	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> -	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> +
> +	clock->vco = clock->n == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> +	clock->dot = clock->p == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  
>  	return clock->dot;
>  }
> @@ -331,10 +332,11 @@ int i9xx_calc_dpll_params(int refclk, struct dpll *clock)
>  {
>  	clock->m = i9xx_dpll_compute_m(clock);
>  	clock->p = clock->p1 * clock->p2;
> -	if (WARN_ON(clock->n + 2 == 0 || clock->p == 0))
> -		return 0;
> -	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
> -	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> +
> +	clock->vco = clock->n + 2 == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
> +	clock->dot = clock->p == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  
>  	return clock->dot;
>  }
> @@ -343,10 +345,11 @@ int vlv_calc_dpll_params(int refclk, struct dpll *clock)
>  {
>  	clock->m = clock->m1 * clock->m2;
>  	clock->p = clock->p1 * clock->p2 * 5;
> -	if (WARN_ON(clock->n == 0 || clock->p == 0))
> -		return 0;
> -	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> -	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> +
> +	clock->vco = clock->n == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> +	clock->dot = clock->p == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  
>  	return clock->dot;
>  }
> @@ -355,11 +358,11 @@ int chv_calc_dpll_params(int refclk, struct dpll *clock)
>  {
>  	clock->m = clock->m1 * clock->m2;
>  	clock->p = clock->p1 * clock->p2 * 5;
> -	if (WARN_ON(clock->n == 0 || clock->p == 0))
> -		return 0;
> -	clock->vco = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(refclk, clock->m),
> -					   clock->n << 22);
> -	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> +
> +	clock->vco = clock->n == 0 ? 0 :
> +		DIV_ROUND_CLOSEST_ULL(mul_u32_u32(refclk, clock->m), clock->n << 22);
> +	clock->dot = clock->p == 0 ? 0 :
> +		DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  
>  	return clock->dot;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center