linux-kernel - Re: [PATCH 2/2] usb: core: phy: fix return value checking about devm_of_phy_get_by

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Date:   Sun, 24 Jun 2018 20:00:01 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     chunfeng.yun@...iatek.com, johan@...nel.org
Cc:     gregkh@...uxfoundation.org, felipe.balbi@...ux.intel.com,
        matthias.bgg@...il.com, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 2/2] usb: core: phy: fix return value checking about devm_of_phy_get_by_index()

Hello Chunfeng,

thank you for the patch!

On Fri, Jun 22, 2018 at 8:33 AM Chunfeng Yun <chunfeng.yun@...iatek.com> wrote:
>
> 1. use IS_ERR() but not IS_ERR_OR_NULL() because devm_of_phy_get_by_index()
>     never return NULL value;
ACK - good catch!

> 2. devm_of_phy_get_by_index() should not fail for a valid index
I have learned that the PHY framework can return -ENODEV if the PHY is:
1. supposed to be handled by the legacy USB PHY framework
2. the PHY node is disabled in devicetree

see [0] for the code in the PHY framework and [1] for the discussion
with Johan (who informed me of case #1, I added him on this mail)

> Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> ---
>  drivers/usb/core/phy.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/core/phy.c b/drivers/usb/core/phy.c
> index 9879767..0f972e1 100644
> --- a/drivers/usb/core/phy.c
> +++ b/drivers/usb/core/phy.c
> @@ -23,14 +23,11 @@ static int usb_phy_roothub_add_phy(struct device *dev, int index,
>                                    struct list_head *list)
>  {
>         struct usb_phy_roothub *roothub_entry;
> -       struct phy *phy = devm_of_phy_get_by_index(dev, dev->of_node, index);
> +       struct phy *phy;
>
> -       if (IS_ERR_OR_NULL(phy)) {
> -               if (!phy || PTR_ERR(phy) == -ENODEV)
> -                       return 0;
> -               else
> -                       return PTR_ERR(phy);
> -       }
> +       phy = devm_of_phy_get_by_index(dev, dev->of_node, index);
> +       if (IS_ERR(phy))
> +               return PTR_ERR(phy);
@Johan can you please review this as well? maybe we need to keep the
-ENODEV check


Regards
Martin


[0] https://elixir.bootlin.com/linux/v4.18-rc2/source/drivers/phy/phy-core.c#L421
[1] https://lkml.org/lkml/2018/4/19/88