Re: [PATCH 2/2] PM / devfreq: qcom: Introduce CCI devfreq driver

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 01/02/2023 17:17, Jun Nie wrote:
> Chanwoo Choi <cwchoi00@gmail.com> 于2023年2月1日周三 19:02写道：
>>
>> Hi,
>>
>> On 23. 2. 1. 17:02, Jun Nie wrote:
>>> Cache Coherent Interconnect (CCI) is used by some Qualcomm SoCs. This
>>> driver is introduced so that its freqency can be adjusted. And regulator
>>> associated with opp table can be also adjusted accordingly which is
>>> shared with cpu cluster.
>>>
>>> Signed-off-by: Jun Nie <jun.nie@linaro.org>
>>> ---
>>>   drivers/devfreq/Kconfig    |   9 +++
>>>   drivers/devfreq/Makefile   |   1 +
>>>   drivers/devfreq/qcom-cci.c | 162 +++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 172 insertions(+)
>>>   create mode 100644 drivers/devfreq/qcom-cci.c
>>>
>>> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
>>> index 9754d8b31621..6f3f1872f3fb 100644
>>> --- a/drivers/devfreq/Kconfig
>>> +++ b/drivers/devfreq/Kconfig
>>> @@ -130,6 +130,15 @@ config ARM_MEDIATEK_CCI_DEVFREQ
>>>          buck voltages and update a proper CCI frequency. Use the notification
>>>          to get the regulator status.
>>>
>>> +config ARM_QCOM_CCI_DEVFREQ
>>> +     tristate "QUALCOMM CCI DEVFREQ Driver"
>>> +     depends on ARCH_QCOM || COMPILE_TEST
>>> +     select DEVFREQ_GOV_PASSIVE
>>> +     help
>>> +       This adds a devfreq driver for Qualcomm Cache Coherent Interconnect which
>>> +       shares the same regulator with the cpu cluster. This driver can track a
>>> +       proper regulator state while CCI frequency is updated.
>>
>> Maybe, this driver use the passive governor because as this description,
>> the regulator is shared with cpu cluster. But, as I commented below,
>> you use the 'userspace' governor in probe. is it right?
>>
>>> +
>>>   config ARM_RK3399_DMC_DEVFREQ
>>>        tristate "ARM RK3399 DMC DEVFREQ Driver"
>>>        depends on (ARCH_ROCKCHIP && HAVE_ARM_SMCCC) || \
>>> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
>>> index bf40d04928d0..f2526d8c168d 100644
>>> --- a/drivers/devfreq/Makefile
>>> +++ b/drivers/devfreq/Makefile
>>> @@ -12,6 +12,7 @@ obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)        += exynos-bus.o
>>>   obj-$(CONFIG_ARM_IMX_BUS_DEVFREQ)    += imx-bus.o
>>>   obj-$(CONFIG_ARM_IMX8M_DDRC_DEVFREQ) += imx8m-ddrc.o
>>>   obj-$(CONFIG_ARM_MEDIATEK_CCI_DEVFREQ)       += mtk-cci-devfreq.o
>>> +obj-$(CONFIG_ARM_QCOM_CCI_DEVFREQ)   += qcom-cci.o
>>>   obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ) += rk3399_dmc.o
>>>   obj-$(CONFIG_ARM_SUN8I_A33_MBUS_DEVFREQ)     += sun8i-a33-mbus.o
>>>   obj-$(CONFIG_ARM_TEGRA_DEVFREQ)              += tegra30-devfreq.o
>>> diff --git a/drivers/devfreq/qcom-cci.c b/drivers/devfreq/qcom-cci.c
>>> new file mode 100644
>>> index 000000000000..21b5f133cddc
>>> --- /dev/null
>>> +++ b/drivers/devfreq/qcom-cci.c
>>> @@ -0,0 +1,162 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Copyright 2023 Linaro Ltd.
>>> + */
>>> +
>>> +#include <linux/clk.h>
>>> +#include <linux/devfreq.h>
>>> +#include <linux/device.h>
>>> +#include <linux/module.h>
>>> +#include <linux/nvmem-consumer.h>
>>> +#include <linux/of_device.h>
>>> +#include <linux/pm_opp.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/slab.h>
>>> +
>>> +#define SPEED_PVS(s, p) ((s << 16) | p)
>>
>> What it meaning of PVS? Could you add the comment for 'PVS' and 's', 'p'?
>>
> This is what I have from Qualcomm code. Maybe others have more info about it.
> Process Voltage Scaling(PVS) Tables defines the voltage and frequency
> value based on the msm-id in SMEM and speedbin blown in the efuse
> combination.
> 
>>> +
>>> +struct qcom_cci {
>>> +     struct devfreq_dev_profile profile;
>>> +     struct devfreq *devfreq;
>>> +     struct clk *clk;
>>> +};
>>> +
>>> +static int qcom_cci_target(struct device *dev,
>>> +             unsigned long *freq, u32 flags)
>>
>> Actually, this line is not long. You can type it on one line as following:
>>
>> static int qcom_cci_target(struct device *dev, unsigned long *freq, u32 flags)
>>
>>> +{
>>> +     struct dev_pm_opp *new_opp;
>>> +     int ret;
>>
>> As I mentioned belwo, this local variable is not needed
>> if just return PTR_ERR(new_opp).
>>
>>> +
>>> +     new_opp = devfreq_recommended_opp(dev, freq, flags);
>>> +     if (IS_ERR(new_opp)) {
>>> +             ret = PTR_ERR(new_opp);
>>> +             dev_err(dev, "failed to get recommended opp: %d\n", ret);
>>> +             return ret;
>>
>> Better to add 'return PTR_ERR(new_opp)' without 'ret' local variable.
>>
>>> +     }
>>> +     dev_pm_opp_put(new_opp);
>>> +
>>> +     return dev_pm_opp_set_rate(dev, *freq);
>>> +}
>>> +
>>> +static int qcom_cci_get_cur_freq(struct device *dev, unsigned long *freq)
>>> +{
>>> +     struct qcom_cci *priv = dev_get_drvdata(dev);
>>> +
>>> +     *freq = clk_get_rate(priv->clk);
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static int qcom_get_dev_version(struct nvmem_cell *speedbin_nvmem)
>>> +{
>>> +     int speed = 0, pvs = 0;
>>> +     u8 *speedbin;
>>> +     size_t len;
>>> +
>>> +     speedbin = nvmem_cell_read(speedbin_nvmem, &len);
>>> +     if (IS_ERR(speedbin))
>>> +             return PTR_ERR(speedbin);
>>> +
>>> +     speed = (speedbin[0xc] >> 2) & 0x7;
>>> +     pvs = (speedbin[0x3] >> 5 & 0x1) | ((speedbin[0x6] >> 2 & 0x3) << 1);
>>
>> Actually, 0xc, 0x3, 0x7, 0x1 and so on. It is impossible to understand
>> the meaning of this hex value. Plesae add the constant defintion
>> for the readability.
>>
> Thanks for pointing it. The bit wise manipulation will be converted
> into nvmem offset and
> bit position in next version. So driver will read out value directly
> without bit shift/mask.
> Other comments will be adopted in next version. Thanks!

Please consider handling everything using the nvmem API. If PVS is split 
into two regions it might be better to parse them separately and then 
combine them in the driver(*), rather than performing such parsing in 
the driver.

(*) while doing the rework of the tsens driver I also faced a similar 
issue. It might be nice to have 'combined' nvmem cells.

-- 
With best wishes
Dmitry