Hello Bjorn,
Few nit-picks.
Thanks & Regards,
Taniya Das.
-----Original Message-----
From: Stephen Boyd <sboyd@xxxxxxxxxx>
Sent: Friday, April 22, 2022 8:13 AM
To: Amit Nischal <anischal@xxxxxxxxxxxxxx>; bjorn.andersson@xxxxxxxxxx; Michael Turquette <mturquette@xxxxxxxxxxxx>; Taniya Das (QUIC) <quic_tdas@xxxxxxxxxxx>
Cc: linux-arm-msm@xxxxxxxxxxxxxxx; linux-clk@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v3] clk: qcom: rcg2: Cache CFG register updates for parked RCGs
Quoting Bjorn Andersson (2022-04-20 20:18:49)
> As GDSCs are turned on and off some associated clocks are momentarily
> enabled for house keeping purposes. For this, and similar, purposes
> the "shared RCGs" will park the RCG on a source clock which is known
> to be available.
> When the RCG is parked, a safe clock source will be selected and
> committed, then the original source would be written back and upon
> enable the change back to the unparked source would be committed.
>
> But starting with SM8350 this fails, as the value in CFG is committed
> by the GDSC handshake and without a ticking parent the GDSC enablement
> will time out.
>
> This becomes a concrete problem if the runtime supended state of a
> device includes disabling such rcg's parent clock. As the device
> attempts to power up the domain again the rcg will fail to enable and
> hence the GDSC enablement will fail, preventing the device from
> returning from the suspended state.
>
> This can be seen in e.g. the display stack during probe on SM8350.
>
> To avoid this problem, the software needs to ensure that the RCG is
> configured to a active parent clock while it is disabled. This is done
> by caching the CFG register content while the shared RCG is parked on
> this safe source.
>
> Writes to M, N and D registers are committed as they are requested.
> New helpers for get_parent() and recalc_rate() are extracted from
> their previous implementations and __clk_rcg2_configure() is modified
> to allow it to operate on the cached value.
>
> Fixes: 7ef6f11887bd ("clk: qcom: Configure the RCGs to a safe source
> as needed")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> ---
Taniya, can you please review?
>
> Changes since v2:
> - Explained the symptoms in commit message
> - Reduced error in clk_rcg2_get_parent() to pr_debug()
> - Reduced the size of the change in __clk_rcg2_configure()
> - Polished comment in clk_rcg2_shared_set_rate()
> - Use clk_hw_is_enabled() in clk_rcg2_shared_set_parent()
>
> drivers/clk/qcom/clk-rcg.h | 2 +
> drivers/clk/qcom/clk-rcg2.c | 124
> ++++++++++++++++++++++++++++--------
> 2 files changed, 100 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
> index 00cea508d49e..012e745794fd 100644
> --- a/drivers/clk/qcom/clk-rcg.h
> +++ b/drivers/clk/qcom/clk-rcg.h
> @@ -140,6 +140,7 @@ extern const struct clk_ops clk_dyn_rcg_ops;
> * @freq_tbl: frequency table
> * @clkr: regmap clock handle
> * @cfg_off: defines the cfg register offset from the CMD_RCGR +
> CFG_REG
> + * @parked_cfg: cached value of the CFG register for parked RCGs
> */
> struct clk_rcg2 {
> u32 cmd_rcgr;
> @@ -150,6 +151,7 @@ struct clk_rcg2 {
> const struct freq_tbl *freq_tbl;
> struct clk_regmap clkr;
> u8 cfg_off;
> + u32 parked_cfg;
> };
>
> #define to_clk_rcg2(_hw) container_of(to_clk_regmap(_hw), struct
> clk_rcg2, clkr) diff --git a/drivers/clk/qcom/clk-rcg2.c
> b/drivers/clk/qcom/clk-rcg2.c index f675fd969c4d..9d218b04aa49 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -73,16 +73,11 @@ static int clk_rcg2_is_enabled(struct clk_hw *hw)
> return (cmd & CMD_ROOT_OFF) == 0; }
>
> -static u8 clk_rcg2_get_parent(struct clk_hw *hw)
> +static u8 __clk_rcg2_get_parent(struct clk_hw *hw, u32 cfg)
> {
> struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> int num_parents = clk_hw_get_num_parents(hw);
> - u32 cfg;
> - int i, ret;
> -
> - ret = regmap_read(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg), &cfg);
> - if (ret)
> - goto err;
> + int i;
>
> cfg &= CFG_SRC_SEL_MASK;
> cfg >>= CFG_SRC_SEL_SHIFT;
> @@ -91,12 +86,27 @@ static u8 clk_rcg2_get_parent(struct clk_hw *hw)
> if (cfg == rcg->parent_map[i].cfg)
> return i;
>
> -err:
> pr_debug("%s: Clock %s has invalid parent, using default.\n",
> __func__, clk_hw_get_name(hw));
> return 0;
> }
>
> +static u8 clk_rcg2_get_parent(struct clk_hw *hw) {
> + struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> + u32 cfg;
> + int ret;
> +
> + ret = regmap_read(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg), &cfg);
> + if (ret) {
> + pr_debug("%s: Unable to read CFG register for %s\n",
> + __func__, clk_hw_get_name(hw));
> + return 0;
> + }
> +
> + return __clk_rcg2_get_parent(hw, cfg); }
> +
> static int update_config(struct clk_rcg2 *rcg) {
> int count, ret;
> @@ -163,12 +173,10 @@ calc_rate(unsigned long rate, u32 m, u32 n, u32
> mode, u32 hid_div) }
>
> static unsigned long
> -clk_rcg2_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
> +__clk_rcg2_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,
> +u32 cfg)
> {
> struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> - u32 cfg, hid_div, m = 0, n = 0, mode = 0, mask;
> -
> - regmap_read(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg), &cfg);
> + u32 hid_div, m = 0, n = 0, mode = 0, mask;
>
> if (rcg->mnd_width) {
> mask = BIT(rcg->mnd_width) - 1; @@ -189,6 +197,17 @@
> clk_rcg2_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
> return calc_rate(parent_rate, m, n, mode, hid_div); }
>
> +static unsigned long
> +clk_rcg2_recalc_rate(struct clk_hw *hw, unsigned long parent_rate) {
> + struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> + u32 cfg;
> +
> + regmap_read(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg), &cfg);
> +
> + return __clk_rcg2_recalc_rate(hw, parent_rate, cfg); }
> +
> static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,
> struct clk_rate_request *req,
> enum freq_policy policy) @@ -262,7
> +281,8 @@ static int clk_rcg2_determine_floor_rate(struct clk_hw *hw,
> return _freq_tbl_determine_rate(hw, rcg->freq_tbl, req,
> FLOOR); }
>
> -static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct
> freq_tbl *f)
> +static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f,
> + u32 *_cfg)
> {
> u32 cfg, mask, d_val, not2d_val, n_minus_m;
> struct clk_hw *hw = &rcg->clkr.hw; @@ -304,15 +324,27 @@
> static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
> cfg |= rcg->parent_map[index].cfg << CFG_SRC_SEL_SHIFT;
> if (rcg->mnd_width && f->n && (f->m != f->n))
> cfg |= CFG_MODE_DUAL_EDGE;
> - return regmap_update_bits(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg),
> - mask, cfg);
> +
> + *_cfg &= ~mask;
> + *_cfg |= cfg;
> +
> + return 0;
> }
>
> static int clk_rcg2_configure(struct clk_rcg2 *rcg, const struct
> freq_tbl *f) {
> + u32 cfg;
> int ret;
>
> - ret = __clk_rcg2_configure(rcg, f);
> + ret = regmap_read(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg), &cfg);
> + if (ret)
> + return ret;
> +
> + ret = __clk_rcg2_configure(rcg, f, &cfg);
> + if (ret)
> + return ret;
> +
> + ret = regmap_write(rcg->clkr.regmap, RCG_CFG_OFFSET(rcg),
> + cfg);
> if (ret)
> return ret;
>
> @@ -979,11 +1011,12 @@ static int clk_rcg2_shared_set_rate(struct clk_hw *hw, unsigned long rate,
> return -EINVAL;
>
> /*
> - * In case clock is disabled, update the CFG, M, N and D registers
> - * and don't hit the update bit of CMD register.
> + * In case clock is disabled, update the M, N and D registers, cache
> + * the CFG value in parked_cfg and don't hit the update bit of CMD
> + * register.
> */
> if (!__clk_is_enabled(hw->clk))
Can we use clk_hw_is_enabled(hw) instead?
> - return __clk_rcg2_configure(rcg, f);
> + return __clk_rcg2_configure(rcg, f, &rcg->parked_cfg);
>
> return clk_rcg2_shared_force_enable_clear(hw, f); } @@
> -1007,6 +1040,11 @@ static int clk_rcg2_shared_enable(struct clk_hw *hw)
> if (ret)
> return ret;
>
> + /* Write back the stored configuration corresponding to current rate */
> + ret = regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, rcg->parked_cfg);
> + if (ret)
> + return ret;
> +
> ret = update_config(rcg);
> if (ret)
> return ret;
> @@ -1017,13 +1055,12 @@ static int clk_rcg2_shared_enable(struct
> clk_hw *hw) static void clk_rcg2_shared_disable(struct clk_hw *hw) {
> struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> - u32 cfg;
>
> /*
> * Store current configuration as switching to safe source would clear
> * the SRC and DIV of CFG register
> */
> - regmap_read(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, &cfg);
> + regmap_read(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG,
> + &rcg->parked_cfg);
>
> /*
> * Park the RCG at a safe configuration - sourced off of safe source.
> @@ -1041,17 +1078,52 @@ static void clk_rcg2_shared_disable(struct clk_hw *hw)
> update_config(rcg);
>
> clk_rcg2_clear_force_enable(hw);
> +}
>
> - /* Write back the stored configuration corresponding to current rate */
> - regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, cfg);
> +static u8 clk_rcg2_shared_get_parent(struct clk_hw *hw) {
> + struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +
> + /* If the shared rcg is parked used the cached cfg instead */
s/used/use
> + if (!__clk_is_enabled(hw->clk))
Can we use clk_hw_is_enabled(hw)?
> + return __clk_rcg2_get_parent(hw, rcg->parked_cfg);
> +
> + return clk_rcg2_get_parent(hw); }
> +
> +static int clk_rcg2_shared_set_parent(struct clk_hw *hw, u8 index) {
> + struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +
> + /* If the shared rcg is parked only update the cached cfg */
> + if (!clk_hw_is_enabled(hw)) {
> + rcg->parked_cfg &= ~CFG_SRC_SEL_MASK;
> + rcg->parked_cfg |= rcg->parent_map[index].cfg <<
> + CFG_SRC_SEL_SHIFT;
> +
> + return 0;
> + }
> +
> + return clk_rcg2_set_parent(hw, index); }
> +
> +static unsigned long
> +clk_rcg2_shared_recalc_rate(struct clk_hw *hw, unsigned long
> +parent_rate) {
> + struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +
> + /* If the shared rcg is parked used the cached cfg instead */
s/used/use
> + if (!__clk_is_enabled(hw->clk))
Can we use clk_hw_is_enabled(hw)?
> + return __clk_rcg2_recalc_rate(hw, parent_rate,
> + rcg->parked_cfg);
> +
> + return clk_rcg2_recalc_rate(hw, parent_rate);
> }
>
> const struct clk_ops clk_rcg2_shared_ops = {
> .enable = clk_rcg2_shared_enable,
> .disable = clk_rcg2_shared_disable,
> - .get_parent = clk_rcg2_get_parent,
> - .set_parent = clk_rcg2_set_parent,
> - .recalc_rate = clk_rcg2_recalc_rate,
> + .get_parent = clk_rcg2_shared_get_parent,
> + .set_parent = clk_rcg2_shared_set_parent,
> + .recalc_rate = clk_rcg2_shared_recalc_rate,
> .determine_rate = clk_rcg2_determine_rate,
> .set_rate = clk_rcg2_shared_set_rate,
> .set_rate_and_parent = clk_rcg2_shared_set_rate_and_parent,
> --
> 2.35.1
>
