Re: [PATCH v3] clk: sunxi-ng: sun50i: h6: Modify GPU clock configuration to support DFS

["Jernej Škrabec" <jernej.skrabec@gmail.com>]

Hi Roman,

Dne sreda, 06. julij 2022 ob 11:46:13 CEST je Roman Stratiienko napisal(a):
> вт, 5 июл. 2022 г. в 21:07, Jernej Škrabec <jernej.skrabec@gmail.com>:
> > Dne torek, 05. julij 2022 ob 18:29:39 CEST je Roman Stratiienko 
napisal(a):
> > > Hi Jernej,
> > > 
> > > вт, 5 июл. 2022 г. в 19:07, Jernej Škrabec <jernej.skrabec@gmail.com>:
> > > > Hi Roman,
> > > > 
> > > > Dne torek, 05. julij 2022 ob 09:52:26 CEST je Roman Stratiienko
> > 
> > napisal(a):
> > > > > Using simple bash script it was discovered that not all CCU
> > > > > registers
> > > > > 
> > > > > can be safely used for DFS, e.g.:
> > > > >     while true
> > > > >     do
> > > > >     
> > > > >         devmem 0x3001030 4 0xb0003e02
> > > > >         devmem 0x3001030 4 0xb0001e02
> > > > >     
> > > > >     done
> > > > > 
> > > > > Script above changes the GPU_PLL multiplier register value. While
> > > > > the
> > > > > script is running, the user should interact with the user interface.
> > > > > 
> > > > > Using this method the following results were obtained:
> > > > > | Register  | Name           | Bits  | Values | Result |
> > > > > | --        | --             | --    | --     | --     |
> > > > > | 0x3001030 | GPU_PLL.MULT   | 15..8 | 20-62  | OK     |
> > > > > | 0x3001030 | GPU_PLL.INDIV  |     1 | 0-1    | OK     |
> > > > > | 0x3001030 | GPU_PLL.OUTDIV |     0 | 0-1    | FAIL   |
> > > > > | 0x3001670 | GPU_CLK.DIV    |  3..0 | ANY    | FAIL   |
> > > > > 
> > > > > DVFS started to work seamlessly once dividers which caused the
> > > > > glitches were set to fixed values.
> > > > > 
> > > > > Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
> > > > > 
> > > > > ---
> > > > > 
> > > > > Changelog:
> > > > > 
> > > > > V2:
> > > > > - Drop changes related to mux
> > > > > - Drop frequency limiting
> > > > > - Add unused dividers initialization
> > > > > 
> > > > > V3:
> > > > > - Adjust comments
> > > > 
> > > > I don't see any comment fixed, at least not to "1", as we discussed.
> > > > Did I
> > > > miss anything?
> > > 
> > > I've added the "bits" word, so now it should sound correct.
> > 
> > Technically it's correct, but this would be third form of comments for
> > fixed bits. Let's stick to the form which is most informative ("Force
> > PLL_GPU output divider to 1"). Ideally, comment would also point to
> > gpu_clk comment for reason why, like it's done for video PLL block
> > already.
> > 
> > > > Also, please add min and max.
> > > 
> > > What is the rationale for additional limits?
> > 
> > If limits are specified in whatever form, they should be added. As I said
> > several times already, vendor code limits PLL frequency to 288 MHz minimum
> > and lists maximum. As experienced a few times before with video PLLs,
> > these are important, otherwise PLL is unstable. For example, OPP table in
> > vendor DT has two operating points lower than 288 MHz, which means it
> > would either lock up or be unstable. In such cases, vendor code actually
> > sets GPU_CLK divider to 2, but we can skip them, because GPU_CLK divider
> > will be hardcoded to 1 with this patch.
> 
> What is the rationale behind vendor's freq limitation?

You have to ask Allwinner. But usually it's a good reason, otherwise they 
wouldn't bother to write such code.

> 
> There's no min_rate field in ccu_nkmp. After I changed it to ccu_nm
> and set limits, the system started to behave unstable with a lot of
> messages in dmesg:
> 
> [   40.089091] panfrost 1800000.gpu: _generic_set_opp_clk_only: failed
> to set clock rate: -22
> [   40.097698] devfreq 1800000.gpu: dvfs failed with (-22) error

Did you remove points below 288 MHz?

> 
> From the other end I have no issues so far with the current version
> and I have a lot of other work to do.
> I think it's a good point to stop any further improvements until
> testing results show any issues with the current version.
> 
> > > CPU_PLL doesn't have these limits. I don't want to make them different.
> > 
> > Why CPU_PLL?
> 
> According to the H6 usermanual only CPU and GPU PLLs support smooth
> clock transition during DFS.

This doesn't mean they have exactly the same limitations. Anyway, I'll merge 
this one. So:

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>

Best regards,
Jernej

> 
> Regards,
> Roman.
> 
> > Why not video PLL? In any case, it doesn't matter if struct looks
> > similar to some other or is unique. Only important thing is that struct
> > describes PLL as best as possible.
> > 
> > > > I also consent to R-B, which you
> > > > didn't include.
> > > 
> > > I was expecting an explicit 'review-by' line. Anyway I can add it and
> > > resend v4 if it's necessary.
> > 
> > If you at least add min and max limits, you can add following tag:
> > Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
> > 
> > If you send it before Friday, it will be in 5.20.
> > 
> > Best regards,
> > Jernej
> > 
> > > Regards,
> > > Roman
> > > 
> > > > Did you resend v2 instead of v3?
> > > > 
> > > > Best regards,
> > > > Jernej
> > > > 
> > > > > ---
> > > > > 
> > > > >  drivers/clk/sunxi-ng/ccu-sun50i-h6.c | 16 +++++++++++++---
> > > > >  1 file changed, 13 insertions(+), 3 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > > b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c index
> > > > > 2ddf0a0da526f..068d1a6b2ebf3
> > > > > 100644
> > > > > --- a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > > +++ b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > > @@ -95,13 +95,13 @@ static struct ccu_nkmp pll_periph1_clk = {
> > > > > 
> > > > >       },
> > > > >  
> > > > >  };
> > > > > 
> > > > > +/* For GPU PLL, using an output divider for DFS causes system to
> > > > > fail
> > > > > */
> > > > > 
> > > > >  #define SUN50I_H6_PLL_GPU_REG                0x030
> > > > >  static struct ccu_nkmp pll_gpu_clk = {
> > > > >  
> > > > >       .enable         = BIT(31),
> > > > >       .lock           = BIT(28),
> > > > >       .n              = _SUNXI_CCU_MULT_MIN(8, 8, 12),
> > > > >       .m              = _SUNXI_CCU_DIV(1, 1), /* input divider */
> > > > > 
> > > > > -     .p              = _SUNXI_CCU_DIV(0, 1), /* output divider
> > > > 
> > > > */
> > > > 
> > > > >       .common         = {
> > > > >       
> > > > >               .reg            = 0x030,
> > > > >               .hw.init        = CLK_HW_INIT("pll-gpu", "osc24M",
> > > > > 
> > > > > @@ -294,9 +294,9 @@ static
> > > > > SUNXI_CCU_M_WITH_MUX_GATE(deinterlace_clk,
> > > > > "deinterlace", static SUNXI_CCU_GATE(bus_deinterlace_clk,
> > > > > "bus-deinterlace", "psi-ahb1-ahb2", 0x62c, BIT(0), 0);
> > > > > 
> > > > > +/* Keep GPU_CLK divider const to avoid DFS instability. */
> > > > > 
> > > > >  static const char * const gpu_parents[] = { "pll-gpu" };
> > > > > 
> > > > > -static SUNXI_CCU_M_WITH_MUX_GATE(gpu_clk, "gpu", gpu_parents,
> > > > > 0x670,
> > > > > -                                    0, 3,    /* M */
> > > > > +static SUNXI_CCU_MUX_WITH_GATE(gpu_clk, "gpu", gpu_parents, 0x670,
> > > > > 
> > > > >                                      24, 1,   /* mux */
> > > > >                                      BIT(31), /* gate */
> > > > >                                      CLK_SET_RATE_PARENT);
> > > > > 
> > > > > @@ -1193,6 +1193,16 @@ static int sun50i_h6_ccu_probe(struct
> > > > > platform_device *pdev) if (IS_ERR(reg))
> > > > > 
> > > > >               return PTR_ERR(reg);
> > > > > 
> > > > > +     /* Force PLL_GPU output divider bits to 0 */
> > > > > +     val = readl(reg + SUN50I_H6_PLL_GPU_REG);
> > > > > +     val &= ~BIT(0);
> > > > > +     writel(val, reg + SUN50I_H6_PLL_GPU_REG);
> > > > > +
> > > > > +     /* Force GPU_CLK divider bits to 0 */
> > > > > +     val = readl(reg + gpu_clk.common.reg);
> > > > > +     val &= ~GENMASK(3, 0);
> > > > > +     writel(val, reg + gpu_clk.common.reg);
> > > > > +
> > > > > 
> > > > >       /* Enable the lock bits on all PLLs */
> > > > >       for (i = 0; i < ARRAY_SIZE(pll_regs); i++) {
> > > > >       
> > > > >               val = readl(reg + pll_regs[i]);
> > > > > 
> > > > > --
> > > > > 2.34.1