Hi Dmitry,
On Tue, Apr 18, 2023 at 1:16 PM Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> ---
> 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
