Hi Mike/Paul,
(sorry for top-posting)
any comments here, what do we do ? Do we split this patch ? Use v1 ? Use
v2 ?
cheers
On Wed, Mar 05, 2014 at 03:50:33PM +0200, Tomi Valkeinen wrote:
> On 20/02/14 21:30, Paul Walmsley wrote:
> > On Wed, 19 Feb 2014, Paul Walmsley wrote:
> >
> >> On Fri, 17 Jan 2014, Tomi Valkeinen wrote:
> >>
> >>> This patch adds a simple method of rounding: during the iteration, the
> >>> code keeps track of the closest rate match. If no exact match is found,
> >>> the closest is returned.
> >>
> >> So that's one possible rounding policy; maybe it works fine for a display
> >> interface PLL, at least for some values of "closest rate". But another
> >> might be "only allow a selection from a set of pre-determined rates
> >> characterized by the silicon validation team". Or another rounding
> >> function might need to select a more distant rate that minimizes jitter,
> >> EMI, or power consumption.
> >
> > Thought about this some more. Do you only need this for the DSS PLL, or
> > do you need it for one of the core OMAP PLLs?
> >
> > If the former, then how about modifying your patch to create a separate
> > round_rate function that's only used for the DSS PLL that implements the
> > behavior that you want?
> >
> > That would eliminate any risk of impacting other users on the system. And
> > would also allow this change to get into the codebase much faster, since
> > there's no need for clk API changes, etc.
>
> How about this one:
>
> From f5a78303411e9192899a6a681acac37f09f4cc3b Mon Sep 17 00:00:00 2001
> From: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> Date: Wed, 15 Jan 2014 11:45:07 +0200
> Subject: [PATCH] ARM: OMAP2+: fix dpll round_rate() to actually round
>
> omap2_dpll_round_rate() doesn't actually round the given rate, even if
> the name and the description so hints. Instead it only tries to find an
> exact rate match, or if that fails, return ~0 as an error.
>
> What this basically means is that the user of the clock needs to know
> what rates the dpll can support, which obviously isn't right.
>
> This patch adds a simple method of rounding: during the iteration, the
> code keeps track of the closest rate match. If no exact match is found,
> the closest is returned.
>
> However, as it is unclear whether current drivers rely on the current
> behavior, the rounding functionality not enabled by default, but by
> setting DPLL_USE_ROUNDED_RATE for the DPLL.
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> ---
> arch/arm/mach-omap2/clkt_dpll.c | 23 ++++++++++++++++++-----
> drivers/clk/ti/dpll.c | 3 +++
> include/linux/clk/ti.h | 1 +
> 3 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/clkt_dpll.c b/arch/arm/mach-omap2/clkt_dpll.c
> index 2649ce445845..fed7538e1eed 100644
> --- a/arch/arm/mach-omap2/clkt_dpll.c
> +++ b/arch/arm/mach-omap2/clkt_dpll.c
> @@ -298,6 +298,8 @@ long omap2_dpll_round_rate(struct clk_hw *hw, unsigned long target_rate,
> struct dpll_data *dd;
> unsigned long ref_rate;
> const char *clk_name;
> + unsigned long diff, closest_diff = ~0;
> + bool use_rounding = clk->flags & DPLL_USE_ROUNDED_RATE;
>
> if (!clk || !clk->dpll_data)
> return ~0;
> @@ -345,20 +347,31 @@ long omap2_dpll_round_rate(struct clk_hw *hw, unsigned long target_rate,
> pr_debug("clock: %s: m = %d: n = %d: new_rate = %lu\n",
> clk_name, m, n, new_rate);
>
> - if (target_rate == new_rate) {
> + diff = max(target_rate, new_rate) - min(target_rate, new_rate);
> +
> + if ((use_rounding && diff < closest_diff) ||
> + (!use_rounding && diff == 0)) {
> + closest_diff = diff;
> +
> dd->last_rounded_m = m;
> dd->last_rounded_n = n;
> - dd->last_rounded_rate = target_rate;
> - break;
> + dd->last_rounded_rate = new_rate;
> +
> + if (diff == 0)
> + break;
> }
> }
>
> - if (target_rate != new_rate) {
> + if (closest_diff == ~0) {
> pr_debug("clock: %s: cannot round to rate %lu\n",
> clk_name, target_rate);
> return ~0;
> }
>
> - return target_rate;
> + if (closest_diff > 0)
> + pr_debug("clock: %s: rounded rate %lu to %lu\n",
> + clk_name, target_rate, dd->last_rounded_rate);
> +
> + return dd->last_rounded_rate;
> }
>
> diff --git a/drivers/clk/ti/dpll.c b/drivers/clk/ti/dpll.c
> index 7e498a44f97d..c5858c46b58c 100644
> --- a/drivers/clk/ti/dpll.c
> +++ b/drivers/clk/ti/dpll.c
> @@ -265,6 +265,9 @@ static void __init of_ti_dpll_setup(struct device_node *node,
> if (dpll_mode)
> dd->modes = dpll_mode;
>
> + if (of_property_read_bool(node, "ti,round-rate"))
> + clk_hw->flags |= DPLL_USE_ROUNDED_RATE;
> +
> ti_clk_register_dpll(&clk_hw->hw, node);
> return;
>
> diff --git a/include/linux/clk/ti.h b/include/linux/clk/ti.h
> index 092b64168d7f..c9ed8b6b8513 100644
> --- a/include/linux/clk/ti.h
> +++ b/include/linux/clk/ti.h
> @@ -155,6 +155,7 @@ struct clk_hw_omap {
> #define INVERT_ENABLE (1 << 4) /* 0 enables, 1 disables */
> #define CLOCK_CLKOUTX2 (1 << 5)
> #define MEMMAP_ADDRESSING (1 << 6)
> +#define DPLL_USE_ROUNDED_RATE (1 << 7) /* dpll's round_rate() returns rounded rate */
>
> /* CM_CLKEN_PLL*.EN* bit values - not all are available for every DPLL */
> #define DPLL_LOW_POWER_STOP 0x1
> --
> 1.8.3.2
>
>
>
--
balbi
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