[Intel-gfx] [PATCH 3/9] drm/i915: fixup i8xx pll limits

[Damien Lespiau]

On Tue, May 21, 2013 at 09:54:53PM +0200, Daniel Vetter wrote:
> So apparently the pll limits in the docs are the real values, but the
> formula actually seems to consistenly use register values. See
> 
> commit 4f7dfb6788dd022446847fbbfbe45e13bedb5be2
> Author: Patrik Jakobsson <patrik.r.jakobsson at gmail.com>
> Date:   Wed Feb 13 22:20:22 2013 +0100
> 
>     drm/i915: Set i9xx sdvo clock limits according to specifications
> 
> On gen2 the situation is a bit more messy: We reuse the code for
> m1/m2/n computation and register frobbing from gen3, so those limits
> need to be in register values (and so need to substract 2 from the doc
> limits).
> 
> But gen2 also stores p1/p2 with 2/1 substracted in the register! For
> those though i8xx_update_pll does the adjustments, but the clock
> computation code assumes it works like on gen3. So for divisor limits
> we must _not_ adjust them to the register values.

I think this deserves a comment for the next one looking at that code.

Also the documented computations for p are:
  gen2: p = (p1 + 2) * 2^(p2 + 1)
  gen3: p = p1 * p2

which lead me to believe we weren't computing the dot clock correctly on
gen2 (but in fact it's fine as p1/p2 are never expressed as register
values, which are not a direct deduction (say on gen 3, p2 = 10 is coded
with 0, p2 = 5 is coded by 1))

So IIUC, we have n, m1, m2 that we express in the "register domain"
while m, p1, p2, p are in the "clock formula domain", for lack of a
better wording. And so the limits follow that.

Otherwise, the patch looks good:

Reviewed-by: Damien Lespiau <damien.lespiau at intel.com>

-- 
Damien

> 
> v2: Extract the common i8xx m/n limits into a single define. This was
> motivated by the mess for the g4x limits where they've all been off in
> different directions, apparently to fix specific bugs ...
> 
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 959c2ae..ea8eb0c 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -84,13 +84,16 @@ intel_fdi_link_freq(struct drm_device *dev)
>  		return 27;
>  }
>  
> +#define I8XX_DPLL_M_N_LIMITS \
> +	.n = { .min = 1, .max = 14 }, \
> +	.m = { .min = 96, .max = 140 }, \
> +	.m1 = { .min = 16, .max = 24 }, \
> +	.m2 = { .min = 4, .max = 14 },
> +
>  static const intel_limit_t intel_limits_i8xx_dvo = {
>  	.dot = { .min = 25000, .max = 350000 },
>  	.vco = { .min = 930000, .max = 1400000 },
> -	.n = { .min = 3, .max = 16 },
> -	.m = { .min = 96, .max = 140 },
> -	.m1 = { .min = 18, .max = 26 },
> -	.m2 = { .min = 6, .max = 16 },
> +	I8XX_DPLL_M_N_LIMITS
>  	.p = { .min = 4, .max = 128 },
>  	.p1 = { .min = 2, .max = 33 },
>  	.p2 = { .dot_limit = 165000,
> @@ -100,10 +103,7 @@ static const intel_limit_t intel_limits_i8xx_dvo = {
>  static const intel_limit_t intel_limits_i8xx_lvds = {
>  	.dot = { .min = 25000, .max = 350000 },
>  	.vco = { .min = 930000, .max = 1400000 },
> -	.n = { .min = 3, .max = 16 },
> -	.m = { .min = 96, .max = 140 },
> -	.m1 = { .min = 18, .max = 26 },
> -	.m2 = { .min = 6, .max = 16 },
> +	I8XX_DPLL_M_N_LIMITS
>  	.p = { .min = 4, .max = 128 },
>  	.p1 = { .min = 1, .max = 6 },
>  	.p2 = { .dot_limit = 165000,
> -- 
> 1.7.11.7
> 
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