linux-kernel - Re: [PATCH 2/2] cpufreq: qcom-hw: Ensure only freq-domain regs are counted in num

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Date:   Fri, 13 Jan 2023 13:41:32 -0600
From:   Rob Herring <robh@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        linux-arm-msm@...r.kernel.org, agross@...nel.org,
        krzysztof.kozlowski@...aro.org, marijn.suijten@...ainline.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cpufreq: qcom-hw: Ensure only freq-domain regs are
 counted in num_domains

On Thu, Jan 12, 2023 at 04:41:50PM +0100, Konrad Dybcio wrote:
> 
> 
> On 12.01.2023 16:37, Bjorn Andersson wrote:
> > On Wed, Jan 11, 2023 at 09:51:25PM +0100, Konrad Dybcio wrote:
> >> In preparation for CPRh-aware OSM programming, change the probe
> >> function so that we determine the number of frequency domains by
> >> counting the number of reg-names entries that begin with
> >> "freq-domain", as the aforementioned changes require introduction
> >> of non-freq-domain register spaces.
> >>
> > 
> > Requiring reg-names would break backwards compatibility with at least
> > sc7280 and sm6115.
> Ouch, you're correct..
> 
> Does checking for reg-names and applying the code flow proposed in this
> patch if found and the existing one if not sound good?

Why support 2 ways?


> Konrad
> > 
> > Regards,
> > Bjorn
> > 
> >> Fixes: 1a6a8b0080b0 ("cpufreq: qcom-hw: Fix reading "reg" with address/size-cells != 2")
> >> Fixes: 054a3ef683a1 ("cpufreq: qcom-hw: Allocate qcom_cpufreq_data during probe")
> >> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> >> ---
> >>  drivers/cpufreq/qcom-cpufreq-hw.c | 34 ++++++++++++++++++++++---------
> >>  1 file changed, 24 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> index 9505a812d6a1..89d5ed267399 100644
> >> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
> >> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> @@ -651,8 +651,9 @@ static int qcom_cpufreq_hw_driver_probe(struct platform_device *pdev)
> >>  	struct device *dev = &pdev->dev;
> >>  	struct device_node *soc_node;
> >>  	struct device *cpu_dev;
> >> +	const char *reg_name;
> >>  	struct clk *clk;
> >> -	int ret, i, num_domains, reg_sz;
> >> +	int ret, i, num_reg_names, num_domains = 0;
> >>  
> >>  	clk = clk_get(dev, "xo");
> >>  	if (IS_ERR(clk))
> >> @@ -684,19 +685,32 @@ static int qcom_cpufreq_hw_driver_probe(struct platform_device *pdev)
> >>  	if (!soc_node)
> >>  		return -EINVAL;
> >>  
> >> -	ret = of_property_read_u32(soc_node, "#address-cells", &reg_sz);
> >> -	if (ret)
> >> +	num_reg_names = of_property_count_strings(dev->of_node, "reg-names");
> >> +	if (num_reg_names <= 0) {
> >> +		ret = num_reg_names ? num_reg_names : -ENODATA;
> >>  		goto of_exit;
> >> +	}
> >>  
> >> -	ret = of_property_read_u32(soc_node, "#size-cells", &i);
> >> -	if (ret)
> >> -		goto of_exit;
> >> +	for (i = 0; i < num_reg_names; i++) {
> >> +		ret = of_property_read_string_index(dev->of_node, "reg-names", i, &reg_name);
> >> +		if (ret < 0)
> >> +			goto of_exit;
> >>  
> >> -	reg_sz += i;
> >> +		/*
> >> +		 * Check if the i-th reg is a freq-domain base, no need to add 1
> >> +		 * more byte for idx, as sizeof counts \0 whereas strlen does not.
> >> +		 */
> >> +		if (strlen(reg_name) == sizeof("freq-domain")) {
> >> +			/* Check if this reg-name begins with "freq-domain" */
> >> +			if (!strncmp(reg_name, "freq-domain", sizeof("freq-domain") - 1))
> >> +				num_domains++;
> >> +		}
> >> +	}
> >>  
> >> -	num_domains = of_property_count_elems_of_size(dev->of_node, "reg", sizeof(u32) * reg_sz);

This code was not great to begin with. Any code parsing 'reg' on it's 
own is suspect IMO. It's a standard property and all parsing of it 
should be in drivers/of/address.c. (Yes, I know there are other cases.)

The reg entries are already available as platform_device resources? Why 
don't you use that? There's also of_address_count(), but I prefer if 
there's a platform device equivalent like we have for interrupts.

Rob