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Message-ID: <1b806538-37d7-40b2-ece9-bcf7792df646@linaro.org>
Date:   Thu, 12 Jan 2023 17:36:06 +0200
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Subject: Re: [PATCH 4/4] clk: qcom: add the driver for the MSM8996 APCS clocks
Content-Language: en-GB
To:     Konrad Dybcio <konrad.dybcio@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Taniya Das <quic_tdas@quicinc.com>,
        Jassi Brar <jassisinghbrar@gmail.com>
Cc:     linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230111191453.2509468-1-dmitry.baryshkov@linaro.org>
 <20230111191453.2509468-5-dmitry.baryshkov@linaro.org>
 <fbec2272-e9b8-207d-e2ce-2f2011640d33@linaro.org>
From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
In-Reply-To: <fbec2272-e9b8-207d-e2ce-2f2011640d33@linaro.org>
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Precedence: bulk

On 12/01/2023 17:23, Konrad Dybcio wrote:
> 
> 
> On 11.01.2023 20:14, Dmitry Baryshkov wrote:
>> Add a simple driver handling the APCS clocks on MSM8996. For now it
>> supports just a single aux clock, linking GPLL0 to CPU and CBF clocks.
>>
>> Note, there is little sense in registering sys_apcs_aux as a child of
>> gpll0. The PLL is always-on. And listing the gpll0 as a property of the
>> apcs would delay its probing until the GCC has been probed (while we
>> would like for the apcs to be probed as early as possible).
>>
>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>> ---
>>   drivers/clk/qcom/Makefile       |  2 +-
>>   drivers/clk/qcom/apcs-msm8996.c | 77 +++++++++++++++++++++++++++++++++
>>   2 files changed, 78 insertions(+), 1 deletion(-)
>>   create mode 100644 drivers/clk/qcom/apcs-msm8996.c
>>
>> diff --git a/drivers/clk/qcom/Makefile b/drivers/clk/qcom/Makefile
>> index f18c446a97ea..ca2f586edb3e 100644
>> --- a/drivers/clk/qcom/Makefile
>> +++ b/drivers/clk/qcom/Makefile
>> @@ -52,7 +52,7 @@ obj-$(CONFIG_MSM_MMCC_8998) += mmcc-msm8998.o
>>   obj-$(CONFIG_QCOM_A53PLL) += a53-pll.o
>>   obj-$(CONFIG_QCOM_A7PLL) += a7-pll.o
>>   obj-$(CONFIG_QCOM_CLK_APCS_MSM8916) += apcs-msm8916.o
>> -obj-$(CONFIG_QCOM_CLK_APCC_MSM8996) += clk-cpu-8996.o
>> +obj-$(CONFIG_QCOM_CLK_APCC_MSM8996) += apcs-msm8996.o clk-cpu-8996.o
>>   obj-$(CONFIG_QCOM_CLK_APCS_SDX55) += apcs-sdx55.o
>>   obj-$(CONFIG_QCOM_CLK_RPM) += clk-rpm.o
>>   obj-$(CONFIG_QCOM_CLK_RPMH) += clk-rpmh.o
>> diff --git a/drivers/clk/qcom/apcs-msm8996.c b/drivers/clk/qcom/apcs-msm8996.c
>> new file mode 100644
>> index 000000000000..2e9959974ed9
>> --- /dev/null
>> +++ b/drivers/clk/qcom/apcs-msm8996.c
>> @@ -0,0 +1,77 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Qualcomm APCS clock controller driver
>> + *
>> + * Copyright (c) 2022, Linaro Limited
>> + * Author: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>> + */
>> +
>> +#include <linux/bits.h>
>> +#include <linux/clk.h>
>> +#include <linux/clk-provider.h>
>> +#include <linux/delay.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/regmap.h>
>> +
>> +#define APCS_AUX_OFFSET	0x50
>> +
>> +#define APCS_AUX_DIV_MASK GENMASK(17, 16)
>> +#define APCS_AUX_DIV_2 0x1
>> +
>> +static int qcom_apcs_msm8996_clk_probe(struct platform_device *pdev)
>> +{
>> +	struct device *dev = &pdev->dev;
>> +	struct device *parent = dev->parent;
>> +	struct regmap *regmap;
>> +	struct clk_hw *hw;
>> +	unsigned int val;
>> +	int ret = -ENODEV;
>> +
>> +	regmap = dev_get_regmap(parent, NULL);
>> +	if (!regmap) {
>> +		dev_err(dev, "failed to get regmap: %d\n", ret);
>> +		return ret;
>> +	}
>> +
>> +	regmap_read(regmap, APCS_AUX_OFFSET, &val);
>> +	regmap_update_bits(regmap, APCS_AUX_OFFSET, APCS_AUX_DIV_MASK,
>> +			   FIELD_PREP(APCS_AUX_DIV_MASK, APCS_AUX_DIV_2));
>> +
>> +	/* Hardware mandated delay */
>> +	udelay(5);
>> +
>> +	/*
>> +	 * Register the clock as fixed rate instead of being a child of gpll0
>> +	 * to let the driver register probe as early as possible.
>> +	 */
> Not sure.. you should keep a vote in GPLL0_ao supplied by XO_A
> and perhaps it would be a better idea to move RPMCC (+deps) and
> GCC to very early initcalls since there's a need for that..
> 
> Maybe it would even allow us to shave some miliseconds from
> boot times, at less things would defer!

That's what I'm trying to stay away from. No deferrals. These pieces 
(APCS, CPU and CBF clocks) should be initialized as early as possible. 
E.g. Qualcomm did all the init manually, even before the devices had a 
chance to probe. Probe deferral means that the device is going to be put 
to the end of the list.

clk-smd-rpmcc and gcc-msm8996 are registered at core_initcall. This is 
the earliest usable init level.

> 
> Konrad
>> +	hw = devm_clk_hw_register_fixed_rate(dev, "sys_apcs_aux", NULL, 0, 300000000);
>> +	if (IS_ERR(hw))
>> +		return PTR_ERR(hw);
>> +
>> +	return devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get, hw);
>> +}
>> +
>> +static struct platform_driver qcom_apcs_msm8996_clk_driver = {
>> +	.probe = qcom_apcs_msm8996_clk_probe,
>> +	.driver = {
>> +		.name = "qcom-apcs-msm8996-clk",
>> +	},
>> +};
>> +
>> +/* Register early enough to fix the clock to be used for other cores */
>> +static int __init qcom_apcs_msm8996_clk_init(void)
>> +{
>> +	return platform_driver_register(&qcom_apcs_msm8996_clk_driver);
>> +}
>> +postcore_initcall(qcom_apcs_msm8996_clk_init);
>> +
>> +static void __exit qcom_apcs_msm8996_clk_exit(void)
>> +{
>> +	platform_driver_unregister(&qcom_apcs_msm8996_clk_driver);
>> +}
>> +module_exit(qcom_apcs_msm8996_clk_exit);
>> +
>> +MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
>> +MODULE_LICENSE("GPL v2");
> "GPL"
> 
>> +MODULE_DESCRIPTION("Qualcomm MSM8996 APCS clock driver");

-- 
With best wishes
Dmitry