linux-kernel - Re: [RESEND v4 2/2] PM / devfreq: mediatek: Introduce MediaTek CCI devfreq driver

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Date:   Thu, 19 May 2022 11:24:43 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Johnson Wang <johnson.wang@...iatek.com>
Cc:     cw00.choi@...sung.com, krzk+dt@...nel.org, robh+dt@...nel.org,
        kyungmin.park@...sung.com, djakov@...nel.org, khilman@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, jia-wei.chang@...iatek.com,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [RESEND v4 2/2] PM / devfreq: mediatek: Introduce MediaTek CCI
 devfreq driver

On Wed, May 18, 2022 at 8:19 PM Johnson Wang <johnson.wang@...iatek.com> wrote:
>
> Hi Chen-Yu,
>
> On Fri, 2022-05-13 at 11:54 +0800, Chen-Yu Tsai wrote:
> > On Fri, May 13, 2022 at 11:31 AM Johnson Wang <
> > johnson.wang@...iatek.com> wrote:
> > >
> > > We introduce a devfreq driver for the MediaTek Cache Coherent
> > > Interconnect
> > > (CCI) used by some MediaTek SoCs.
> > >
> > > In this driver, we use the passive devfreq driver to get target
> > > frequencies
> > > and adjust voltages accordingly. In MT8183 and MT8186, the MediaTek
> > > CCI
> > > is supplied by the same regulators with the little core CPUs.
> > >
> > > Signed-off-by: Jia-Wei Chang <jia-wei.chang@...iatek.com>
> > > Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
> > > Acked-by: Chanwoo Choi <cw00.choi@...sung.com>
> > > ---
> > > This patch depends on "devfreq-testing"[1].
> > > [1]
> > > https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/log/?h=devfreq-testing__;!!CTRNKA9wMg0ARbw!zzOSoso9udvDV3h6kYlmizFtbn3ACA5aS2jCAjKyvtu4z0fobv1mD5uF9YbPSme8l_NnR05unTxkZfDdzohu8asWZQ$
> > >
> > > ---
> > >  drivers/devfreq/Kconfig           |  10 +
> > >  drivers/devfreq/Makefile          |   1 +
> > >  drivers/devfreq/mtk-cci-devfreq.c | 474
> > > ++++++++++++++++++++++++++++++
> > >  3 files changed, 485 insertions(+)
> > >  create mode 100644 drivers/devfreq/mtk-cci-devfreq.c
> > >
> > > diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> > > index 87eb2b837e68..9754d8b31621 100644
> > > --- a/drivers/devfreq/Kconfig
> > > +++ b/drivers/devfreq/Kconfig
> > > @@ -120,6 +120,16 @@ config ARM_TEGRA_DEVFREQ
> > >           It reads ACTMON counters of memory controllers and
> > > adjusts the
> > >           operating frequencies and voltages with OPP support.
> > >
> > > +config ARM_MEDIATEK_CCI_DEVFREQ
> > > +       tristate "MEDIATEK CCI DEVFREQ Driver"
> > > +       depends on ARM_MEDIATEK_CPUFREQ || COMPILE_TEST
> > > +       select DEVFREQ_GOV_PASSIVE
> > > +       help
> > > +         This adds a devfreq driver for MediaTek Cache Coherent
> > > Interconnect
> > > +         which is shared the same regulators with the cpu cluster.
> > > It can track
> > > +         buck voltages and update a proper CCI frequency. Use the
> > > notification
> > > +         to get the regulator status.
> > > +
> > >  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 0b6be92a25d9..bf40d04928d0 100644
> > > --- a/drivers/devfreq/Makefile
> > > +++ b/drivers/devfreq/Makefile
> > > @@ -11,6 +11,7 @@ obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)     +=
> > > governor_passive.o
> > >  obj-$(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_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/mtk-cci-devfreq.c
> > > b/drivers/devfreq/mtk-cci-devfreq.c
> > > new file mode 100644
> > > index 000000000000..aa8c37eb4a06
> > > --- /dev/null
> > > +++ b/drivers/devfreq/mtk-cci-devfreq.c
> > > @@ -0,0 +1,474 @@

[...]

> > > +       if (IS_ERR(drv->sram_reg))
> > > +               drv->sram_reg = NULL;
> > > +       else {
> > > +               ret = regulator_enable(drv->sram_reg);
> > > +               if (ret) {
> > > +                       dev_err(dev, "failed to enable sram
> > > regulator\n");
> > > +                       goto out_free_resources;
> > > +               }
> > > +       }
> > > +
> > > +       /*
> > > +        * We assume min voltage is 0 and tracking target voltage
> > > using
> > > +        * min_volt_shift for each iteration.
> > > +        * The retry_max is 3 times of expeted iteration count.
> >
> > expected?
> >
> Maybe "the maximum" will be more appropriate?


I was merely pointing out a typo in "expeted".

Looking at it again, I'm not sure why retry attempts are tied to the voltage.


ChenYu