netdev - Re: [PATCH v4] net: usb: r8152: Add in new Devices that are supported for Mac-Passthru

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Date:   Fri, 13 May 2022 16:55:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Ober <dober6023@...il.com>
Cc:     linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        davem@...emloft.net, hayeswang@...ltek.com, aaron.ma@...onical.com,
        markpearson@...ovo.com, dober@...ovo.com
Subject: Re: [PATCH v4] net: usb: r8152: Add in new Devices that are
 supported for Mac-Passthru

On Fri, 13 May 2022 08:49:06 -0400 David Ober wrote:
> Lenovo Thunderbolt 4 Dock, and other Lenovo USB Docks are using the
> original Realtek USB ethernet Vendor and Product IDs
> If the Network device is Realtek verify that it is on a Lenovo USB hub
> before enabling the passthru feature
> 
> This also adds in the device IDs for the Lenovo USB Dongle and one other
> USB-C dock
> 
> V2 fix formating of code
> V3 remove Generic define for Device ID 0x8153 and change it to use value
> V4 rearrange defines and case statement to put them in better order
> 
> Signed-off-by: David Ober <dober6023@...il.com>
> ---
>  drivers/net/usb/r8152.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> index c2da3438387c..d8f2d4b85db4 100644
> --- a/drivers/net/usb/r8152.c
> +++ b/drivers/net/usb/r8152.c
> @@ -771,7 +771,9 @@ enum rtl8152_flags {
>  };
>  
>  #define DEVICE_ID_THINKPAD_THUNDERBOLT3_DOCK_GEN2	0x3082
> +#define DEVICE_ID_THINKPAD_USB_C_DONGLE			0x720c
>  #define DEVICE_ID_THINKPAD_USB_C_DOCK_GEN2		0xa387
> +#define DEVICE_ID_THINKPAD_USB_C_DOCK_GEN3		0x3062
>  
>  struct tally_counter {
>  	__le64	tx_packets;
> @@ -9646,6 +9648,14 @@ static int rtl8152_probe(struct usb_interface *intf,
>  		switch (le16_to_cpu(udev->descriptor.idProduct)) {
>  		case DEVICE_ID_THINKPAD_THUNDERBOLT3_DOCK_GEN2:
>  		case DEVICE_ID_THINKPAD_USB_C_DOCK_GEN2:
> +		case DEVICE_ID_THINKPAD_USB_C_DOCK_GEN3:
> +		case DEVICE_ID_THINKPAD_USB_C_DONGLE:
> +			tp->lenovo_macpassthru = 1;
> +		}
> +	} else if ((le16_to_cpu(udev->descriptor.idVendor) == VENDOR_ID_REALTEK) &&
> +		   (le16_to_cpu(udev->parent->descriptor.idVendor) == VENDOR_ID_LENOVO)) {

The parenthesis around the condition are unnecessary. If the compiler
does not warn it's okay to skip parenthesis. checkpatch should warn
about this. We assume kernel developers know the C operator precedence.

I think you should factor these checks out to a separate helper tho.
Create a helper like:

static bool rtl8152_needs_lenovo_macpassthru(dev)

that can use local variables to avoid the tediously long and repeated
le16_to_cpu(...) lines. Then just assign:

	tp->lenovo_macpassthru = rtl8152_needs_lenovo_macpassthru(dev);

Please CC Bjørn Mork <bjorn@...k.no> since he commented on the previous
version. I'd personally also love to see this solved in user space...
but have no clear idea how.

> +		switch (le16_to_cpu(udev->descriptor.idProduct)) {
> +		case 0x8153:
>  			tp->lenovo_macpassthru = 1;
>  		}
>  	}