Date:   Sat, 10 Jun 2023 14:14:18 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Leo Yan <leo.yan@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 17/22] interconnect: qcom: icc-rpm: Control bus rpmcc
 from icc



On 10.06.2023 13:58, Stephan Gerhold wrote:
> On Fri, Jun 09, 2023 at 10:19:22PM +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@...aro.org>
>> ---
>>  drivers/interconnect/qcom/icc-rpm.c | 116 +++++++++++++++++++-----------------
>>  drivers/interconnect/qcom/icc-rpm.h |  13 ++--
>>  drivers/interconnect/qcom/msm8996.c |   1 -
>>  drivers/interconnect/qcom/sdm660.c  |   1 -
>>  4 files changed, 66 insertions(+), 65 deletions(-)
>>
>> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
>> index b8ecf9538ab9..6d40815c5401 100644
>> --- a/drivers/interconnect/qcom/icc-rpm.c
>> +++ b/drivers/interconnect/qcom/icc-rpm.c
>> [...]
>> @@ -364,49 +363,50 @@ 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)
>> +		return clk_set_rate(qp->bus_clk, 1000ULL * max(active_rate, sleep_rate));
> 
> Something like the min_t(u64, rate, LONG_MAX)* that was there in the old
> code is still needed for the clk_set_rate(). The reason is that the rate
> parameter in clk_set_rate() is unsigned long (32-bit on ARM32) while you
> do the calculation in fixed u64. This can easily overflow and then the
> higher bits will just be cut off.
> 
> Consider the following on ARM32:
> 
> 	u64 rate = 1ULL << 32 = 4294967296ULL;
> 	clk_set_rate(clk, rate);
> 
> This actually does clk_set_rate(clk, 0) because the upper 32-bit will
> just be truncated. So the min() is needed to ensure that we really set
> the highest possible.
> 
> Also see commit a7d9436a6c85 ("interconnect: qcom: rpm: Prevent integer
> overflow in rate") [1].
> 
> * I'm not sure why I used LONG_MAX instead of ULONG_MAX back then.
Ughh can we kill arm32 already? It only causes problems :P

Thanks for spotting this..

> 
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a7d9436a6c85fcb8843c910fd323dcd7f839bf63
> 
>> [...]
>>  int qnoc_probe(struct platform_device *pdev)
>>  {
>>  	struct device *dev = &pdev->dev;
>> @@ -448,6 +448,18 @@ int qnoc_probe(struct platform_device *pdev)
>>  	if (!qp->intf_clks)
>>  		return -ENOMEM;
>>  
>> +	if (desc->bus_clk_desc) {
>> +		qp->bus_clk_desc = devm_kzalloc(dev, sizeof(*qp->bus_clk_desc),
>> +						GFP_KERNEL);
>> +		if (!qp->bus_clk_desc)
>> +			return -ENOMEM;
>> +
>> +		qp->bus_clk_desc = desc->bus_clk_desc;
>> +	} else if (!IS_ERR(devm_clk_get(dev, "bus"))) {
>> +		/* Some older SoCs may have a single non-RPM-owned bus clock. */
>> +		qp->bus_clk = devm_clk_get(dev, "bus");
>> +	}
> 
> Hm, looks like you're requesting the clock twice? devm_clk_get()
> allocates memory internally so that's not ideal. It would be better to
> call it just once and store the result. Or do you actually want
> devm_clk_get_optional(dev, "bus") maybe? The error handling is a bit
> weird here.
Hmm, right.. I think it should go something like this:

qp->bus_clk = devm_clk_get(dev, "bus");
if (IS_ERR(qp->bus_clk) && PTR_ERR(qp->bus_clk) == -ENOENT)
	qp->bus_clk = NULL;
else if (IS_ERR(qp->bus_clk))
	return PTR_ERR(qp->bus_clk)


> 
>> [...]
>> @@ -490,13 +498,11 @@ int qnoc_probe(struct platform_device *pdev)
>>  	}
>>  
>>  regmap_done:
>> -	ret = devm_clk_bulk_get(dev, qp->num_bus_clks, qp->bus_clks);
>> -	if (ret)
>> -		return ret;
>> -
>> -	ret = clk_bulk_prepare_enable(qp->num_bus_clks, qp->bus_clks);
>> -	if (ret)
>> -		return ret;
> 
> I guess we need dt-binding updates so we can drop the clocks from the
> device tree? They're not valid anymore after you remove them from
> clk-smd-rpm.c so it would be good to drop them from the DTs to avoid
> confusion.
I wanted to handle that separately as the bindings are technically still
correct.. There'll be a need for some deprecation though.

> 
>> +	if (qp->bus_clk) {
>> +		ret = clk_prepare_enable(qp->bus_clk);
>> +		if (ret)
>> +			return ret;
>> +	}
> 
> The clk_* APIs have internal NULL checks for optional clocks so you
> could also omit the if statement and call it unconditionally.
Ack

Konrad
> 
>>  
>>  	ret = devm_clk_bulk_get(dev, qp->num_intf_clks, qp->intf_clks);
>>  	if (ret)
>> @@ -566,7 +572,8 @@ int qnoc_probe(struct platform_device *pdev)
>>  	icc_provider_deregister(provider);
>>  err_remove_nodes:
>>  	icc_nodes_remove(provider);
>> -	clk_bulk_disable_unprepare(qp->num_bus_clks, qp->bus_clks);
>> +	if (qp->bus_clk)
>> +		clk_disable_unprepare(qp->bus_clk);
>>  
> 
> Same here.
> 
>>  	return ret;
>>  }
>> @@ -578,7 +585,8 @@ int qnoc_remove(struct platform_device *pdev)
>>  
>>  	icc_provider_deregister(&qp->provider);
>>  	icc_nodes_remove(&qp->provider);
>> -	clk_bulk_disable_unprepare(qp->num_bus_clks, qp->bus_clks);
>> +	if (qp->bus_clk)
>> +		clk_disable_unprepare(qp->bus_clk);
>>  
> 
> And here.
> 
> Thanks,
> Stephan

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