Re: [Intel-gfx] [PATCH] drm/i915/cnl: Simplify dco_fraction calculation.

[Ville Syrjälä]

On Wed, Nov 15, 2017 at 10:42:57AM -0800, Rodrigo Vivi wrote:
> I confess I never fully understood that previous calculation,
> so this is not a "fix". But let's simplify this math
> so poor brains like mine can read and make some sense of
> it in the future.
> 
> v2: Don't follow the spec since that gives invalid
> values and it is also confusing. This Ville's
> version is much simpler.
> v3: Use u64 cast instead of declaring a u64 dco. (Ville).
> 
> Cc: Ville Syrjälä 
> Cc: Mika Kahola 
> Cc: Manasi Navare 
> Cc: James Ausmus 
> Signed-off-by: Rodrigo Vivi 

Reviewed-by: Ville Syrjälä 

> ---
>  drivers/gpu/drm/i915/intel_dpll_mgr.c | 9 ++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c 
> b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> index 361b7102b602..51c5ae4e9116 100644
> --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> @@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(struct 
> skl_wrpll_params *params,
> u32 dco_freq, u32 ref_freq,
> int pdiv, int qdiv, int kdiv)
>  {
> + u32 dco;
> +
>   switch (kdiv) {
>   case 1:
>   params->kdiv = 1;
> @@ -2189,9 +2191,10 @@ static void cnl_wrpll_params_populate(struct 
> skl_wrpll_params *params,
>   params->qdiv_ratio = qdiv;
>   params->qdiv_mode = (qdiv == 1) ? 0 : 1;
>  
> - params->dco_integer = div_u64(dco_freq, ref_freq);
> - params->dco_fraction = div_u64((div_u64((uint64_t)dco_freq<<15, 
> (uint64_t)ref_freq) -
> - ((uint64_t)params->dco_integer<<15)) * 
> 0x8000, 0x8000);
> + dco = div_u64((u64)dco_freq << 15, ref_freq);
> +
> + params->dco_integer = dco >> 15;
> + params->dco_fraction = dco & 0x7fff;
>  }
>  
>  static bool
> -- 
> 2.13.6

-- 
Ville Syrjälä
Intel OTC
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[Intel-gfx] [PATCH] drm/i915/cnl: Simplify dco_fraction calculation.

[Rodrigo Vivi]

I confess I never fully understood that previous calculation,
so this is not a "fix". But let's simplify this math
so poor brains like mine can read and make some sense of
it in the future.

v2: Don't follow the spec since that gives invalid
values and it is also confusing. This Ville's
version is much simpler.
v3: Use u64 cast instead of declaring a u64 dco. (Ville).

Cc: Ville Syrjälä 
Cc: Mika Kahola 
Cc: Manasi Navare 
Cc: James Ausmus 
Signed-off-by: Rodrigo Vivi 
---
 drivers/gpu/drm/i915/intel_dpll_mgr.c | 9 ++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c 
b/drivers/gpu/drm/i915/intel_dpll_mgr.c
index 361b7102b602..51c5ae4e9116 100644
--- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
@@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(struct 
skl_wrpll_params *params,
  u32 dco_freq, u32 ref_freq,
  int pdiv, int qdiv, int kdiv)
 {
+   u32 dco;
+
switch (kdiv) {
case 1:
params->kdiv = 1;
@@ -2189,9 +2191,10 @@ static void cnl_wrpll_params_populate(struct 
skl_wrpll_params *params,
params->qdiv_ratio = qdiv;
params->qdiv_mode = (qdiv == 1) ? 0 : 1;
 
-   params->dco_integer = div_u64(dco_freq, ref_freq);
-   params->dco_fraction = div_u64((div_u64((uint64_t)dco_freq<<15, 
(uint64_t)ref_freq) -
-   ((uint64_t)params->dco_integer<<15)) * 
0x8000, 0x8000);
+   dco = div_u64((u64)dco_freq << 15, ref_freq);
+
+   params->dco_integer = dco >> 15;
+   params->dco_fraction = dco & 0x7fff;
 }
 
 static bool
-- 
2.13.6

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Re: [Intel-gfx] [PATCH] drm/i915/cnl: Simplify dco_fraction calculation.

[Ville Syrjälä]

On Tue, Nov 14, 2017 at 03:51:26PM -0800, Rodrigo Vivi wrote:
> I confess I never fully understood that previous calculation,
> so this is not a "fix". But let's simplify this math
> so poor brains like mine can read and make some sense of
> it in the future.
> 
> v2: Don't follow the spec since that gives invalid
> values and it is also confusing. This Ville's
> version is much simpler.
> 
> Cc: Ville Syrjälä 
> Cc: Mika Kahola 
> Cc: Manasi Navare 
> Cc: James Ausmus 
> Signed-off-by: Rodrigo Vivi 
> ---
>  drivers/gpu/drm/i915/intel_dpll_mgr.c | 9 ++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c 
> b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> index 361b7102b602..f9651accecc9 100644
> --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> @@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(struct 
> skl_wrpll_params *params,
> u32 dco_freq, u32 ref_freq,
> int pdiv, int qdiv, int kdiv)
>  {
> + u64 dco;
> +
>   switch (kdiv) {
>   case 1:
>   params->kdiv = 1;
> @@ -2189,9 +2191,10 @@ static void cnl_wrpll_params_populate(struct 
> skl_wrpll_params *params,
>   params->qdiv_ratio = qdiv;
>   params->qdiv_mode = (qdiv == 1) ? 0 : 1;
>  
> - params->dco_integer = div_u64(dco_freq, ref_freq);
> - params->dco_fraction = div_u64((div_u64((uint64_t)dco_freq<<15, 
> (uint64_t)ref_freq) -
> - ((uint64_t)params->dco_integer<<15)) * 
> 0x8000, 0x8000);
> + dco = dco_freq;
> + dco = div_u64(dco << 15, ref_freq);

A bit wasteful putting the result into a u64. The cast I had in my
earlier proposal should do.

> + params->dco_integer = dco >> 15;
> + params->dco_fraction = dco & 0x7fff;
>  }
>  
>  static bool
> -- 
> 2.13.6

-- 
Ville Syrjälä
Intel OTC
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[Intel-gfx] [PATCH] drm/i915/cnl: Simplify dco_fraction calculation.

[Rodrigo Vivi]

I confess I never fully understood that previous calculation,
so this is not a "fix". But let's simplify this math
so poor brains like mine can read and make some sense of
it in the future.

v2: Don't follow the spec since that gives invalid
values and it is also confusing. This Ville's
version is much simpler.

Cc: Ville Syrjälä 
Cc: Mika Kahola 
Cc: Manasi Navare 
Cc: James Ausmus 
Signed-off-by: Rodrigo Vivi 
---
 drivers/gpu/drm/i915/intel_dpll_mgr.c | 9 ++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c 
b/drivers/gpu/drm/i915/intel_dpll_mgr.c
index 361b7102b602..f9651accecc9 100644
--- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
@@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(struct 
skl_wrpll_params *params,
  u32 dco_freq, u32 ref_freq,
  int pdiv, int qdiv, int kdiv)
 {
+   u64 dco;
+
switch (kdiv) {
case 1:
params->kdiv = 1;
@@ -2189,9 +2191,10 @@ static void cnl_wrpll_params_populate(struct 
skl_wrpll_params *params,
params->qdiv_ratio = qdiv;
params->qdiv_mode = (qdiv == 1) ? 0 : 1;
 
-   params->dco_integer = div_u64(dco_freq, ref_freq);
-   params->dco_fraction = div_u64((div_u64((uint64_t)dco_freq<<15, 
(uint64_t)ref_freq) -
-   ((uint64_t)params->dco_integer<<15)) * 
0x8000, 0x8000);
+   dco = dco_freq;
+   dco = div_u64(dco << 15, ref_freq);
+   params->dco_integer = dco >> 15;
+   params->dco_fraction = dco & 0x7fff;
 }
 
 static bool
-- 
2.13.6

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