[PATCH v3] clk: sunxi-ng: sun50i: h6: Modify GPU clock configuration to support DFS
Roman Stratiienko
r.stratiienko at gmail.com
Wed Jul 6 02:46:13 PDT 2022
вт, 5 июл. 2022 г. в 21:07, Jernej Škrabec <jernej.skrabec at 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 at 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 at 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?
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
>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.
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 at 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
>
>
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