linux-kernel - Re: [PATCH v7 1/5] usb: phy: add usb phy notify port status API

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Date:   Mon, 24 Jul 2023 07:50:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Stanley Chang <stanley_chang@...ltek.com>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Roy Luo <royluo@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Flavio Suligoi <f.suligoi@...m.it>,
        Ray Chi <raychi@...gle.com>, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v7 1/5] usb: phy: add usb phy notify port status API

On Fri, Jul 07, 2023 at 02:47:00PM +0800, Stanley Chang wrote:
> In Realtek SoC, the parameter of usb phy is designed to can dynamic
> tuning base on port status. Therefore, add a notify callback of phy
> driver when usb port status change.
> 
> The Realtek phy driver is designed to dynamically adjust disconnection
> level and calibrate phy parameters. When the device connected bit changes
> and when the disconnected bit changes, do port status change notification:
> 
> Check if portstatus is USB_PORT_STAT_CONNECTION and portchange is
> USB_PORT_STAT_C_CONNECTION.
> 1. The device is connected, the driver lowers the disconnection level and
>    calibrates the phy parameters.
> 2. The device disconnects, the driver increases the disconnect level and
>    calibrates the phy parameters.
> 
> When controller to notify connect that device is already ready. If we
> adjust the disconnection level in notify_connect, the disconnect may have
> been triggered at this stage. So we need to change that as early as
> possible. Therefore, we add an api to notify phy the port status changes.

How do you know that the disconnect will not have already been triggered
at this point, when the status changes?


> 
> Signed-off-by: Stanley Chang <stanley_chang@...ltek.com>
> ---
> v6 to v7 change:
>     No change
> v5 to v6 change:
>     No change
> v4 to v5 change:
>     No change
> v3 to v4 change:
>     Fix the warning for checkpatch with strict.
> v2 to v3 change:
>     Add more comments about the reason for adding this api
> v1 to v2 change:
>     No change
> ---
>  drivers/usb/core/hub.c  | 13 +++++++++++++
>  include/linux/usb/phy.h | 13 +++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index a739403a9e45..8433ff89dea6 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -614,6 +614,19 @@ static int hub_ext_port_status(struct usb_hub *hub, int port1, int type,
>  		ret = 0;
>  	}
>  	mutex_unlock(&hub->status_mutex);
> +
> +	if (!ret) {
> +		struct usb_device *hdev = hub->hdev;
> +
> +		if (hdev && !hdev->parent) {

Why the check for no parent?  Please document that here in a comment.

> +			struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
> +
> +			if (hcd->usb_phy)
> +				usb_phy_notify_port_status(hcd->usb_phy,
> +							   port1 - 1, *status, *change);
> +		}
> +	}
> +

This is safe to notify with the hub mutex unlocked?  Again, a comment
would be helpful to future people explaining why that is so.

thanks,

greg k-h