linux-kernel - Re: [PATCH v6 3/5] phy: core: Add support for phy power down & power up

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Message-ID: <bd6fc826-94b9-f539-a37e-820ab49b9d14@linaro.org>
Date:   Mon, 19 Sep 2022 20:29:56 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc:     helgaas@...nel.org, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        mka@...omium.org, quic_vbadigan@...cinc.com,
        quic_hemantk@...cinc.com, quic_nitegupt@...cinc.com,
        quic_skananth@...cinc.com, quic_ramkri@...cinc.com,
        manivannan.sadhasivam@...aro.org, swboyd@...omium.org,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        "open list:GENERIC PHY FRAMEWORK" <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH v6 3/5] phy: core: Add support for phy power down & power
 up

On 14/09/2022 17:50, Krishna Chaitanya Chundru wrote:
> 
> On 9/9/2022 2:34 PM, Dmitry Baryshkov wrote:
>> On Fri, 9 Sept 2022 at 11:45, Krishna chaitanya chundru
>> <quic_krichai@...cinc.com> wrote:
>>> Introducing phy power down/up callbacks for allowing to park the
>>> link-state in L1ss without holding any PCIe resources during
>>> system suspend.
>>>
>>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
>>> ---
>>>   drivers/phy/phy-core.c  | 30 ++++++++++++++++++++++++++++++
>>>   include/linux/phy/phy.h | 20 ++++++++++++++++++++
>>>   2 files changed, 50 insertions(+)
>>>
>>> diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
>>> index d93ddf1..1b0b757 100644
>>> --- a/drivers/phy/phy-core.c
>>> +++ b/drivers/phy/phy-core.c
>>> @@ -441,6 +441,36 @@ int phy_set_speed(struct phy *phy, int speed)
>>>   }
>>>   EXPORT_SYMBOL_GPL(phy_set_speed);
>>>
>>> +int phy_power_down(struct phy *phy)
>>> +{
>>> +       int ret;
>>> +
>>> +       if (!phy || !phy->ops->power_down)
>>> +               return 0;
>>> +
>>> +       mutex_lock(&phy->mutex);
>>> +       ret = phy->ops->power_down(phy);
>>> +       mutex_unlock(&phy->mutex);
>>> +
>>> +       return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(phy_power_down);
>>> +
>>> +int phy_power_up(struct phy *phy)
>>> +{
>>> +       int ret;
>>> +
>>> +       if (!phy || !phy->ops->power_up)
>>> +               return 0;
>>> +
>>> +       mutex_lock(&phy->mutex);
>>> +       ret = phy->ops->power_up(phy);
>>> +       mutex_unlock(&phy->mutex);
>>> +
>>> +       return ret;
>>> +}
>> As it can be seen from the phy_power_off(), the PHY can be a shared
>> resource, with the power_count counting the number of users that
>> requested the PHY to be powered up. By introducing suc calls you break
>> directly into this by allowing a single user to power down the PHY, no
>> matter how many other users have requested the PHY to stay alive.
> 
> can we use same power_count in this function also here and restrict the 
> single user to
> 
> power down the PHY same like phy_power_off?.

What is the difference between power_off() and power_down()?


-- 
With best wishes
Dmitry