linux-kernel - Re: [PATCH 03/11] clk: sunxi-ng: a83t: Support new timing mode for mmc2 clock

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Date:   Tue, 18 Jul 2017 16:47:58 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 03/11] clk: sunxi-ng: a83t: Support new timing mode for
 mmc2 clock

On Mon, Jul 17, 2017 at 06:12:35PM +0800, Chen-Yu Tsai wrote:
> On Mon, Jul 17, 2017 at 5:14 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > Hi,
> >
> > On Fri, Jul 14, 2017 at 02:42:54PM +0800, Chen-Yu Tsai wrote:
> >> The MMC2 clock supports a new timing mode. When the new mode is active,
> >> the output clock rate is halved.
> >>
> >> This patch sets the feature flag for the new timing mode, and adds
> >> a pre-divider based on the mode bit.
> >>
> >> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> >> ---
> >>  drivers/clk/sunxi-ng/ccu-sun8i-a83t.c | 38 +++++++++++++++++++++++++++--------
> >>  1 file changed, 30 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/clk/sunxi-ng/ccu-sun8i-a83t.c b/drivers/clk/sunxi-ng/ccu-sun8i-a83t.c
> >> index 947f9f6e05d2..ee6688e9b361 100644
> >> --- a/drivers/clk/sunxi-ng/ccu-sun8i-a83t.c
> >> +++ b/drivers/clk/sunxi-ng/ccu-sun8i-a83t.c
> >> @@ -418,14 +418,36 @@ static SUNXI_CCU_PHASE(mmc1_sample_clk, "mmc1-sample", "mmc1",
> >>  static SUNXI_CCU_PHASE(mmc1_output_clk, "mmc1-output", "mmc1",
> >>                      0x08c, 8, 3, 0);
> >>
> >> -/* TODO Support MMC2 clock's new timing mode. */
> >> -static SUNXI_CCU_MP_WITH_MUX_GATE(mmc2_clk, "mmc2", mod0_default_parents,
> >> -                               0x090,
> >> -                               0, 4,         /* M */
> >> -                               16, 2,        /* P */
> >> -                               24, 2,        /* mux */
> >> -                               BIT(31),      /* gate */
> >> -                               0);
> >> +/*
> >> + * MMC2 supports both old and new timing modes. When the new timing
> >> + * mode is active, the output clock rate is halved by two. Here we
> >> + * treat it as a variable pre-divider. Note that the pre-divider is
> >> + * _not_ included in the possible factors during a set clock rate
> >> + * operation. It is only read out.
> >> + */
> >> +static const struct ccu_mux_var_prediv mmc2_new_timing_predivs[] = {
> >> +     { .index = 0, .shift = 30, .width = 1 },
> >> +     { .index = 1, .shift = 30, .width = 1 },
> >> +};
> >> +static struct ccu_mp mmc2_clk = {
> >> +     .enable = BIT(31),
> >> +     .m      = _SUNXI_CCU_DIV(0, 4),
> >> +     .p      = _SUNXI_CCU_DIV(16, 2),
> >> +     .mux    = {
> >> +             .shift  = 24,
> >> +             .width  = 2,
> >> +             .var_predivs    = mmc2_new_timing_predivs,
> >> +             .n_var_predivs  = ARRAY_SIZE(mmc2_new_timing_predivs),
> >> +     },
> >> +     .common         = {
> >> +             .reg            = 0x090,
> >> +             .features       = CCU_FEATURE_MMC_TIMING_SWITCH,
> >> +             .hw.init        = CLK_HW_INIT_PARENTS("mmc2",
> >> +                                                   mod0_default_parents,
> >> +                                                   &ccu_mp_ops,
> >> +                                                   CLK_GET_RATE_NOCACHE),
> >> +     },
> >> +};
> >
> > Treating the new bit seems a bit of a hack to me. It only works
> > because we're not evaluating the various pre-dividers during a
> > determine_rate (and set_rate), but it might change in the future, and
> > we will break all our eMMC controllers then.
> >
> > Since they're quite special, I was thinking about creating a new MMC
> > clock type? We're going to use it on a number of SoCs, and we'll be
> > able to model it properly, without crippling the regular and generic
> > MP clocks.
> 
> Yes that should be doable. I could put them in the same file and
> reuse all the existing MP clocks stuff by wrapping them in new
> functions that check the timing mode bit.
> 
> Would that work for you?

Yep, it does.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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