Re: [PATCH 2/7] clk: thead: th1520-ap: Poll for PLL lock and wait for stability

Drew Fustini
2025-11-26T14:52:08Z

On Thu, Nov 20, 2025 at 01:14:11PM +0000, Yao Zi wrote:
> All PLLs found on TH1520 SoC take 21250ns at maximum to lock, and their
> lock status is indicated by register PLL_STS (offset 0x80 inside AP
> clock controller). We should poll the register to ensure the PLL
> actually locks after enabling it.
>
> Furthermore, a 30us delay is added after enabling the PLL, after which
> the PLL could be considered stable as stated by vendor clock code.
>
> Fixes: 56a48c1833aa ("clk: thead: add support for enabling/disabling PLLs")
> Signed-off-by: Yao Zi <ziyao@disroot.org>
> ---
> drivers/clk/thead/clk-th1520-ap.c | 34 +++++++++++++++++++++++++++++--
> 1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/thead/clk-th1520-ap.c b/drivers/clk/thead/clk-th1520-ap.c
[...]
> +/*
> + * All PLLs in TH1520 take 21250ns at maximum to lock, let's take its double
> + * for safety.
> + */
> +#define TH1520_PLL_LOCK_TIMEOUT_US 44
> +#define TH1520_PLL_STABLE_DELAY_US 30

I'm taking a second look at this and I think it might be best to add a
define for the polling loop delay of 5. It could be helpful when other
people read the code later.

[...]
> + ret = regmap_read_poll_timeout_atomic(pll->common.map, TH1520_PLL_STS,
> + reg, reg & pll->lock_sts_mask,
> + 5, TH1520_PLL_LOCK_TIMEOUT_US);

The loop delay is only used here but I think using a #define would make
it more readable.

Other than that:
Reviewed-by: Drew Fustini <fustini@kernel.org>

If no other changes are needed I could fix this up on apply. Let's see
what other comments there may be. It's too late for me to send a 6.19
clk pull request so this will have to target the next merge window. I
can put it into linux-next once 6.19-rc1 is released.

Thanks,
Drew