linux-kernel - Re: [PATCH v2 1/5] phy: amlogic: enable/disable clkin during Amlogic USB PHY init/exit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAFBinCDyhBQ5Nob38EmXor1PtcO09dRdReDTW+tc5CN4i20HhA@mail.gmail.com>
Date:   Sun, 23 Apr 2023 19:42:25 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Dmitry Rokosov <ddrokosov@...rdevices.ru>
Cc:     gregkh@...uxfoundation.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, neil.armstrong@...aro.org,
        khilman@...libre.com, jbrunet@...libre.com,
        mturquette@...libre.com, vkoul@...nel.org, kishon@...nel.org,
        hminas@...opsys.com, Thinh.Nguyen@...opsys.com,
        yue.wang@...ogic.com, hanjie.lin@...ogic.com,
        kernel@...rdevices.ru, rockosov@...il.com,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-phy@...ts.infradead.org
Subject: Re: [PATCH v2 1/5] phy: amlogic: enable/disable clkin during Amlogic
 USB PHY init/exit

Hi Dmitry,

On Tue, Apr 18, 2023 at 1:16 PM Dmitry Rokosov <ddrokosov@...rdevices.ru> wrote:
>
> Previously, all Amlogic boards used the XTAL clock as the default board
> clock for the USB PHY input, so there was no need to enable it.
> However, with the introduction of new Amlogic SoCs like the A1 family,
> the USB PHY now uses a gated clock. Hence, it is necessary to enable
> this gated clock during the PHY initialization sequence, or disable it
> during the PHY exit, as appropriate.
>
> Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
> ---
>  drivers/phy/amlogic/phy-meson-g12a-usb2.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/phy/amlogic/phy-meson-g12a-usb2.c b/drivers/phy/amlogic/phy-meson-g12a-usb2.c
> index 9d1efa0d9394..80938751da4f 100644
> --- a/drivers/phy/amlogic/phy-meson-g12a-usb2.c
> +++ b/drivers/phy/amlogic/phy-meson-g12a-usb2.c
> @@ -172,10 +172,16 @@ static int phy_meson_g12a_usb2_init(struct phy *phy)
>         int ret;
>         unsigned int value;
>
> -       ret = reset_control_reset(priv->reset);
> +       ret = clk_prepare_enable(priv->clk);
>         if (ret)
>                 return ret;
>
> +       ret = reset_control_reset(priv->reset);
> +       if (ret) {
> +               clk_disable_unprepare(priv->clk);
> +               return ret;
> +       }
> +
This part looks good. You asked why I suggested this approach instead
of enabling the clock at probe time and only now I have time to reply
to it.
Consider the following scenario:
- modprobe phy-meson-g12a-usb2
- modprobe dwc3-meson-g12a (this will call phy_init)
- rmmod dwc3-meson-g12a (this will call phy_exit)

If the clock was enabled at probe time then it would only be disabled
when using rmmod phy-meson-g12a-usb2.
By manually calling clk_prepare_enable/clk_disable_unprepare we ensure
that the clock gets disabled when we don't need the PHY anymore.
Whether this makes any difference in terms of power draw: I can't say.

>         udelay(RESET_COMPLETE_TIME);
>
>         /* usb2_otg_aca_en == 0 */
> @@ -277,8 +283,11 @@ static int phy_meson_g12a_usb2_init(struct phy *phy)
>  static int phy_meson_g12a_usb2_exit(struct phy *phy)
>  {
>         struct phy_meson_g12a_usb2_priv *priv = phy_get_drvdata(phy);
> +       int ret = reset_control_reset(priv->reset);
> +
> +       clk_disable_unprepare(priv->clk);
>
> -       return reset_control_reset(priv->reset);
> +       return ret;
I think this can cause issues in case when reset_control_reset returns
an error: If I understand the code in phy-core.c correctly it will
only decrease the init ref-count if exit returns 0.
Whenever phy_exit is called for the second time
clk_disable_unprepare() will be called with a clock ref-count of 0, so
it'll likely print some warning.

My suggestion is to return early if reset_control_reset() fails and
not call clk_disable_unprepare() in that case.
What do you think?


Best regards,
Martin