Re: [PATCH 4/5] clk: sunxi-ng: a64: Add constraints on PLL-VIDEO0's n/m ratio

Jernej Škrabec
2024-01-09T20:30:16Z

Dne nedelja, 31. december 2023 ob 10:10:40 CET je Frank Oltmanns napisal(a):
>
> On 2023-12-19 at 17:54:19 +0100, Jernej Škrabec <jernej.skrabec@gmail.com> wrote:
> > Dne ponedeljek, 18. december 2023 ob 14:35:22 CET je Frank Oltmanns napisal(a):
> >> The Allwinner A64 manual lists the following constraint for the
> >> PLL-VIDEO0 clock: 8 <= N/M <= 25
> >>
> >> Use this constraint.
> >>
> >> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
> >> ---
> >> drivers/clk/sunxi-ng/ccu-sun50i-a64.c | 8 ++++++--
> >> 1 file changed, 6 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> index c034ac027d1c..75d839da446c 100644
> >> --- a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> +++ b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> @@ -68,7 +68,8 @@ static SUNXI_CCU_NM_WITH_SDM_GATE_LOCK(pll_audio_base_clk, "pll-audio-base",
> >> BIT(28), /* lock */
> >> CLK_SET_RATE_UNGATE);
> >>
> >> -static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_CLOSEST(pll_video0_clk, "pll-video0",
> >> +static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_FEAT_NM_RATIO(pll_video0_clk,
> >> + "pll-video0",
> >> "osc24M", 0x010,
> >> 192000000, /* Minimum rate */
> >> 1008000000, /* Maximum rate */
>
> I just realized that adding the whole ratio limits for ccu_nm is
> superfluous as you could just as well express them in for of a minimum
> and maximum range:
> Since 8 <= N/M <= 25 and parent_rate = 24 MHz, therefore
> 192 MHz <= rate <= 600 MHz.

Good point!

>
> These absolute limits are also listed in Allwinner's A64 manual.
>
> BUT, here the upper limit was raised to 1008 MHz:
> 5de39acaf34604bd04834f092479cf4dcc946dd "clk: sunxi-ng: a64: Add max.
> rate constraint to video PLL"
>
> With this upper limit the ratio limitation is effectively:
> 8 <= N/M <= 42
>
> Icenowy Zheng (added to CC) had the reasonable explanation that this was
> used in the BSP kernel, so we should probably stick to that and ditch
> the two PLL-VIDEO0 related patches. What are your thoughts on that?

Ok, it seems that these patches are really superfluous. Remove them for v2.

Best regards,
Jernej

>
> >> @@ -80,7 +81,10 @@ static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_CLOSEST(pll_video0_clk, "pll-vid
> >> 297000000, /* frac rate 1 */
> >> BIT(31), /* gate */
> >> BIT(28), /* lock */
> >> - CLK_SET_RATE_UNGATE);
> >> + CLK_SET_RATE_UNGATE,
> >> + CCU_FEATURE_FRACTIONAL |
> >> + CCU_FEATURE_CLOSEST_RATE,
> >
> > Above flags are unrelated change, put them in new patch if needed.
> >
> > Best regards,
> > Jernej
> >
> >> + 8, 25); /* min/max nm ratio */
> >>
> >> static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK(pll_ve_clk, "pll-ve",
> >> "osc24M", 0x018,
> >>
> >>