Re: [PATCH v3 18/23] interconnect: qcom: icc-rpm: Control bus rpmcc from icc

[Stephan Gerhold]

On Mon, Jun 12, 2023 at 08:24:35PM +0200, Konrad Dybcio wrote:
> The sole purpose of bus clocks that were previously registered with
> rpmcc was to convey the aggregated bandwidth to RPM. There's no good
> reason to keep them outside the interconnect framework, as it only
> adds to the plentiful complexity.
> 
> Add the required code to handle these clocks from within SMD RPM ICC.
> 
> RPM-owned bus clocks are no longer considered a thing, but sadly we
> have to allow for the existence of HLOS-owned bus clocks, as some
> (mostly older) SoCs (ab)use these for bus scaling (e.g. MSM8998 and
> &mmcc AHB_CLK_SRC).
> 
> This in turn is trivially solved with a single *clk, which is filled
> and used iff qp.bus_clk_desc is absent and we have a "bus" clock-names
> entry in the DT node.
> 
> This change should(tm) be fully compatible with all sorts of old
> Device Trees as far as the interconnect functionality goes (modulo
> abusing bus clock handles, but that's a mistake in and of itself).
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>

Would be nice to add a comment here already that you're breaking
compatbility with the qcom,icc.h. It's a bit hidden otherwise.

> ---
>  drivers/interconnect/qcom/icc-rpm.c | 114 ++++++++++++++++++++----------------
>  drivers/interconnect/qcom/icc-rpm.h |  13 ++--
>  drivers/interconnect/qcom/msm8996.c |   1 -
>  drivers/interconnect/qcom/sdm660.c  |   1 -
>  4 files changed, 66 insertions(+), 63 deletions(-)
> 
> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
> index b8ecf9538ab9..5ffcf5ca8914 100644
> --- a/drivers/interconnect/qcom/icc-rpm.c
> +++ b/drivers/interconnect/qcom/icc-rpm.c
> @@ -49,7 +49,7 @@
>  #define NOC_QOS_MODE_FIXED_VAL		0x0
>  #define NOC_QOS_MODE_BYPASS_VAL		0x2
>  
> -#define ICC_BUS_CLK_MIN_RATE		19200000ULL
> +#define ICC_BUS_CLK_MIN_RATE		19200ULL /* kHz */
>  
>  static int qcom_icc_set_qnoc_qos(struct icc_node *src)
>  {
> @@ -338,11 +338,10 @@ static int qcom_icc_set(struct icc_node *src, struct icc_node *dst)
>  	struct qcom_icc_node *src_qn = NULL, *dst_qn = NULL;
>  	struct icc_provider *provider;
>  	u64 sum_bw;
> -	u64 rate;
> +	u64 active_rate, sleep_rate;
>  	u64 agg_avg[QCOM_ICC_NUM_BUCKETS], agg_peak[QCOM_ICC_NUM_BUCKETS];
>  	u64 max_agg_avg;
> -	int ret, i;
> -	int bucket;
> +	int ret;
>  
>  	src_qn = src->data;
>  	if (dst)
> @@ -364,49 +363,54 @@ static int qcom_icc_set(struct icc_node *src, struct icc_node *dst)
>  			return ret;
>  	}
>  
> -	for (i = 0; i < qp->num_bus_clks; i++) {
> -		/*
> -		 * Use WAKE bucket for active clock, otherwise, use SLEEP bucket
> -		 * for other clocks.  If a platform doesn't set interconnect
> -		 * path tags, by default use sleep bucket for all clocks.
> -		 *
> -		 * Note, AMC bucket is not supported yet.
> -		 */
> -		if (!strcmp(qp->bus_clks[i].id, "bus_a"))
> -			bucket = QCOM_ICC_BUCKET_WAKE;
> -		else
> -			bucket = QCOM_ICC_BUCKET_SLEEP;
> -
> -		rate = icc_units_to_bps(max(agg_avg[bucket], agg_peak[bucket]));
> -		do_div(rate, src_qn->buswidth);
> -		rate = min_t(u64, rate, LONG_MAX);
> -
> -		/*
> -		 * Downstream checks whether the requested rate is zero, but it makes little sense
> -		 * to vote for a value that's below the lower threshold, so let's not do so.
> -		 */
> -		if (bucket == QCOM_ICC_BUCKET_WAKE && qp->keep_alive)
> -			rate = max(ICC_BUS_CLK_MIN_RATE, rate);
> -
> -		if (qp->bus_clk_rate[i] == rate)
> -			continue;
> -
> -		ret = clk_set_rate(qp->bus_clks[i].clk, rate);
> -		if (ret) {
> -			pr_err("%s clk_set_rate error: %d\n",
> -			       qp->bus_clks[i].id, ret);
> +	/* Some providers don't have a bus clock to scale */
> +	if (!qp->bus_clk_desc && !qp->bus_clk)
> +		return 0;
> +
> +	/* Intentionally keep the rates in kHz as that's what RPM accepts */
> +	active_rate = max(agg_avg[QCOM_SMD_RPM_ACTIVE_STATE],
> +			  agg_peak[QCOM_SMD_RPM_ACTIVE_STATE]);
> +	do_div(active_rate, src_qn->buswidth);
> +
> +	sleep_rate = max(agg_avg[QCOM_SMD_RPM_SLEEP_STATE],
> +			 agg_peak[QCOM_SMD_RPM_SLEEP_STATE]);
> +	do_div(sleep_rate, src_qn->buswidth);
> +
> +	/*
> +	 * Downstream checks whether the requested rate is zero, but it makes little sense
> +	 * to vote for a value that's below the lower threshold, so let's not do so.
> +	 */
> +	if (qp->keep_alive)
> +		active_rate = max(ICC_BUS_CLK_MIN_RATE, active_rate);
> +
> +	/* Some providers have a non-RPM-owned bus clock - convert kHz->Hz for the CCF */
> +	if (qp->bus_clk) {
> +		active_rate = max_t(u64, active_rate, sleep_rate);
> +		/* ARM32 caps clk_set_rate arg to u32.. Nothing we can do about that! */
> +		active_rate = min_t(u64, 1000ULL * active_rate, ULONG_MAX);
> +		return clk_set_rate(qp->bus_clk, active_rate);
> +	}
> +
> +	/* RPM only accepts <=INT_MAX rates */
> +	active_rate = min_t(u32, active_rate, INT_MAX);
> +	sleep_rate = min_t(u32, sleep_rate, INT_MAX);
> +
> +	if ((active_rate != qp->bus_clk_rate[QCOM_SMD_RPM_ACTIVE_STATE]) ||
> +	    (sleep_rate != qp->bus_clk_rate[QCOM_SMD_RPM_SLEEP_STATE])) {
> +		ret = qcom_icc_rpm_set_bus_rate(qp->bus_clk_desc,
> +						active_rate,
> +						sleep_rate);
> +		if (ret)
>  			return ret;

Hm, do we have to set both rates together in all cases? If cpufreq is
quickly changing frequencies (and therefore active-only ICC bandwidths)
it should be sufficient to make one call into RPM and leave the sleep
rate as-is. Especially because you already cache the two rates
separately.

AFAICT downstream updates the contexts completely separately, so I don't
think it updates both rates at once either. And actually even the old
code before this patch didn't do that :D

Thanks,
Stephan