RE: [PATCH v2 2/2] OMAP3630 SDRC: Change in DVFS Latency Formula for OMAP3630

Sripathy, Vishwanath
2010-03-19T13:17:43Z

> -----Original Message-----
> From: K, Ambresh
> Sent: Thursday, March 18, 2010 12:48 PM
> To: Gurav , Pramod
> Cc: linux-omap@vger.kernel.org; Sripathy, Vishwanath
> Subject: Re: [PATCH v2 2/2] OMAP3630 SDRC: Change in DVFS Latency Formula for
> OMAP3630
>
> Gurav , Pramod wrote:
> > This patch uses new formula to derive the dpll3 clock Stabilization
> > delay during DVFS for OMAP3630. The formula used is :
> > Latency = 2 * SYS_CLK + 10 * CLKOUTX2
> >
> > 1usec buffer time is added for safety.
> >
> > Signed-off-by: Vishwanath Sripathy <vishwanath.bs@ti.com>
> > Signed-off-by: Pramod Gurav <pramod.gurav@ti.com>
> >
> > ---
> > arch/arm/mach-omap2/clkt34xx_dpll3m2.c | 60
> ++++++++++++++++++++++----------
> > 1 files changed, 41 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/arm/mach-omap2/clkt34xx_dpll3m2.c b/arch/arm/mach-
> omap2/clkt34xx_dpll3m2.c
> > index 29421b1..58979ec 100644
> > --- a/arch/arm/mach-omap2/clkt34xx_dpll3m2.c
> > +++ b/arch/arm/mach-omap2/clkt34xx_dpll3m2.c
> > @@ -40,6 +40,9 @@
> > #define SHIFT_DPLL_N 8
> > #define SHIFT_DPLL_M2 27
> >
> > +#define AVOID_TRUNC_1000 1000
> > +#define AVOID_TRUNC_100 100
> > +
> > /*
> > * CORE DPLL (DPLL3) M2 divider rate programming functions
> > *
> > @@ -67,7 +70,7 @@ int omap3_core_dpll_m2_set_rate(struct clk *clk, unsigned
> long rate)
> > u32 clk_sel_regval;
> > u32 core_dpll_mul_m, core_dpll_div_n, core_dpll_clkoutdiv_m2;
> > u32 sys_clk_rate, sdrc_clk_stab;
> > - u32 refclk, clkoutx2, switch_latency;
> > + u32 refclk, clkoutx2, switch_latency, dpll_lock_freq;
> > unsigned int delay_sram;
> >
> > if (!clk || !rate)
> > @@ -100,28 +103,47 @@ int omap3_core_dpll_m2_set_rate(struct clk *clk,
> unsigned long rate)
> > core_dpll_clkoutdiv_m2 = (clk_sel_regval >> SHIFT_DPLL_M2) &
> > DPLL_M2_MASK;
> > sys_clk_rate = clk_get_rate(sys_ck_p);
> > -
> > sys_clk_rate = sys_clk_rate / CYCLES_PER_MHZ;
> >
> > - /* wait time for L3 clk stabilization = 4*REFCLK + 8*CLKOUTX2 */
> > - refclk = (4 * (core_dpll_div_n + 1)) / sys_clk_rate;
> > - clkoutx2 = ((core_dpll_div_n + 1) * core_dpll_clkoutdiv_m2) /
> > - (sys_clk_rate * core_dpll_mul_m * 2);
> > - switch_latency = refclk + 8 * clkoutx2;
> > -
> > - /* Adding 2us to sdrc clk stab */
> > - sdrc_clk_stab = switch_latency + 2;
> > -
> > - delay_sram = delay_sram_val();
> > -
> > - /*
> > - * Calculate the number of MPU cycles
> > - * to wait for SDRC to stabilize
> > - */
> > -
> > _mpurate = arm_fck_p->rate / CYCLES_PER_MHZ;
> > + delay_sram = delay_sram_val();
> >
> > - c = ((sdrc_clk_stab * _mpurate) / (delay_sram * 2));
> > + if (cpu_is_omap3630()) {
> > + /*
> > + * wait time for L3 clk stabilization =
> > + * 2*SYS_CLK + 10*CLKOUTX2
> > + */
> > + /*
> > + * To avoid truncation of floating values, AVOID_TRUNC_1000 &
> > + * AVOID_TRUNC_100 are multiplied and divided appropriately
> > + */
> > + refclk = 2 * (AVOID_TRUNC_1000 / sys_clk_rate);
> > + dpll_lock_freq = (AVOID_TRUNC_1000 * AVOID_TRUNC_100 *
> > + (core_dpll_div_n + 1))/
> > + (2 * sys_clk_rate * core_dpll_mul_m);
> > + clkoutx2 = 10 * (dpll_lock_freq * core_dpll_clkoutdiv_m2) /
> > + AVOID_TRUNC_100;
> > + switch_latency = refclk + clkoutx2;
> > +
> > + /* Adding 1000 nano seconds to sdrc clk stab */
> > + sdrc_clk_stab = switch_latency + 1000;
> > + c = ((sdrc_clk_stab * _mpurate) /
> > + (delay_sram * 2 * AVOID_TRUNC_1000));
> > + } else {
> > + /* wait time for L3 clk stabilization = 4*REFCLK + 8*CLKOUTX2 */
> > + refclk = (4 * (core_dpll_div_n + 1)) / sys_clk_rate;
> > + clkoutx2 = ((core_dpll_div_n + 1) * core_dpll_clkoutdiv_m2) /
> > + (sys_clk_rate * core_dpll_mul_m * 2);
> > + switch_latency = refclk + 8 * clkoutx2;
> > +
> > + /* Adding 2us to sdrc clk stab */
> > + sdrc_clk_stab = switch_latency + 2;
> > + /*
> > + * Calculate the number of MPU cycles to wait for
> > + * SDRC to stabilize
> > + */
> > + c = ((sdrc_clk_stab * _mpurate) / (delay_sram * 2));
> > + }
> >
> -PFA,
>
> - Attached patch provides further optimized 3630 & 3430 path for
> calculating M2 stablization delay.
>
> - The formula used to compute clkoutx2, is actually calculating for
> clkoutm2x2 according to trm clkoutx2 = (Fref * 2 * M)/ (N + 1).
> (Thanks to Eduardo for pointing this).
>
No, CLKOUTX2 is dependent on M2. Pls refer to table 3-45 (DPLL Operating Mode and Latency) in 3630 TRM Version D.

Regards
Vishwa
> Thanks,
> Ambresh
>
> > pr_debug("m = %d, n = %d, m2 =%d\n", core_dpll_mul_m, core_dpll_div_n,
> > core_dpll_clkoutdiv_m2);