Re: [PATCH 2/2] clk: sunxi-ng: sun50i: a64: Add 2x fixed post-divider to MMC module clocks

[Chen-Yu Tsai <wens@csie.org>]

On Wed, Dec 6, 2017 at 11:56 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> Hi,
>
> On Wed, Dec 06, 2017 at 10:30:26AM +0800, Chen-Yu Tsai wrote:
>> On Wed, Dec 6, 2017 at 3:59 AM, Maxime Ripard
>> <maxime.ripard@free-electrons.com> wrote:
>> > Hi,
>> >
>> > On Mon, Dec 04, 2017 at 01:19:12PM +0800, Chen-Yu Tsai wrote:
>> >> On the A64, the MMC module clocks are fixed in the new timing mode,
>> >> i.e. they do not have a bit to select the mode. These clocks have
>> >> a 2x divider somewhere between the clock and the MMC module.
>> >>
>> >> To be consistent with other SoCs supporting the new timing mode,
>> >> we model the 2x divider as a fixed post-divider on the MMC module
>> >> clocks.
>> >>
>> >> This patch adds the post-dividers to the MMC clocks.
>> >>
>> >> Signed-off-by: Chen-Yu Tsai <wens@csie.org>
>> >
>> > I had a doubt applying that one... sorry.
>> >
>> >> ---
>> >>  drivers/clk/sunxi-ng/ccu-sun50i-a64.c | 57 +++++++++++++++++++++++------------
>> >>  1 file changed, 37 insertions(+), 20 deletions(-)
>> >>
>> >> diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
>> >> index 2bb4cabf802f..ee9c12cf3f08 100644
>> >> --- a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
>> >> +++ b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
>> >> @@ -400,28 +400,45 @@ static SUNXI_CCU_MP_WITH_MUX_GATE(nand_clk, "nand", mod0_default_parents, 0x080,
>> >>                                 BIT(31),      /* gate */
>> >>                                 0);
>> >>
>> >> +/*
>> >> + * MMC clocks are the new timing mode (see A83T & H3) variety, but without
>> >> + * the mode switch. This means they have a 2x post divider between the clock
>> >> + * and the MMC module. This is not documented in the manual, but is taken
>> >> + * into consideration when setting the mmc module clocks in the BSP kernel.
>> >> + * Without it, MMC performance is degraded.
>> >> + *
>> >> + * We model it here to be consistent with other SoCs supporting this mode.
>> >> + * The alternative would be to add the 2x multiplier when setting the MMC
>> >> + * module clock in the MMC driver, just for the A64.
>> >> + */
>> >>  static const char * const mmc_default_parents[] = { "osc24M", "pll-periph0-2x",
>> >>                                                   "pll-periph1-2x" };
>> >> -static SUNXI_CCU_MP_WITH_MUX_GATE(mmc0_clk, "mmc0", mmc_default_parents, 0x088,
>> >> -                               0, 4,         /* M */
>> >> -                               16, 2,        /* P */
>> >> -                               24, 2,        /* mux */
>> >> -                               BIT(31),      /* gate */
>> >> -                               0);
>> >> -
>> >> -static SUNXI_CCU_MP_WITH_MUX_GATE(mmc1_clk, "mmc1", mmc_default_parents, 0x08c,
>> >> -                               0, 4,         /* M */
>> >> -                               16, 2,        /* P */
>> >> -                               24, 2,        /* mux */
>> >> -                               BIT(31),      /* gate */
>> >> -                               0);
>> >> -
>> >> -static SUNXI_CCU_MP_WITH_MUX_GATE(mmc2_clk, "mmc2", mmc_default_parents, 0x090,
>> >> -                               0, 4,         /* M */
>> >> -                               16, 2,        /* P */
>> >> -                               24, 2,        /* mux */
>> >> -                               BIT(31),      /* gate */
>> >> -                               0);
>> >> +static SUNXI_CCU_MP_WITH_MUX_GATE_POSTDIV(mmc0_clk, "mmc0",
>> >> +                                       mmc_default_parents, 0x088,
>> >> +                                       0, 4,         /* M */
>> >> +                                       16, 2,        /* P */
>> >> +                                       24, 2,        /* mux */
>> >> +                                       BIT(31),      /* gate */
>> >> +                                       2,            /* post-div */
>> >> +                                       0);
>> >> +
>> >> +static SUNXI_CCU_MP_WITH_MUX_GATE_POSTDIV(mmc1_clk, "mmc1",
>> >> +                                       mmc_default_parents, 0x08c,
>> >> +                                       0, 4,         /* M */
>> >> +                                       16, 2,        /* P */
>> >> +                                       24, 2,        /* mux */
>> >> +                                       BIT(31),      /* gate */
>> >> +                                       2,            /* post-div */
>> >> +                                       0);
>> >> +
>> >
>> > Are you sure that the divider there for the non-eMMC clocks? Usually,
>> > the new mode is only here for the eMMC, so we would divide the rate by
>> > two in the non-eMMC case.
>>
>> The new mode is there for all MMC controllers. The other two MMC
>> controllers even have the old/new timing mode switch. In case you
>> forgot we have ".need_new_timings" set for the A64 compatible.
>
> But then, shouldn't we model them as such, using the work you did on
> the A83t clocks?

On the A64, the clocks don't have the switch. Only the MMC controller
does. On the A83T, both do.

ChenYu

>> But to eliminate any doubts or concerns, I've rerun tests for the
>> micro SD card, instead of the eMMC. And yes the results are the same,
>> 2x improvement (12 MB/s vs 23.7 MB/s).
>
> Ok, good.
>
> Thanks!
> Maxime
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com