linux-kernel - Re: [PATCH] usb: gadget: Do not handle OS Descriptors config separately

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Date:   Thu, 16 Feb 2023 12:40:12 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Elson Roy Serrao <quic_eserrao@...cinc.com>
Cc:     Thinh.Nguyen@...opsys.com, balbi@...nel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        quic_wcheng@...cinc.com, quic_jackp@...cinc.com
Subject: Re: [PATCH] usb: gadget: Do not handle OS Descriptors config
 separately

On Mon, Feb 13, 2023 at 03:45:25PM -0800, Elson Roy Serrao wrote:
> Consider a multi-configuration composition in which the last
> configuration uses OS descriptors. Since this configuration will
> be sent first, the host may choose this config if it matches the
> choosing criteria and ignore the user configured order of the
> multi-config composition.

That is up to the host, so why is this an issue?

> Moreover linux based hosts do not re-order
> the received configurations based on their indices but process them
> in FIFO order.

s/linux/Linux/

> This may result in the host never choosing the user
> desired configuration because of the re-order caused by sending the
> OS descriptor config first. To avoid this, follow the user configured
> order and do not handle OS descriptor config separately.

I do not understand, what reordering is happening, and by whom?

> 
> Signed-off-by: Elson Roy Serrao <quic_eserrao@...cinc.com>

What commit does this fix?

> ---
>  drivers/usb/gadget/composite.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index fa7dd6c..685003a 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -589,18 +589,9 @@ static int config_desc(struct usb_composite_dev *cdev, unsigned w_value)
>  	w_value &= 0xff;
>  
>  	pos = &cdev->configs;
> -	c = cdev->os_desc_config;
> -	if (c)
> -		goto check_config;
> -
>  	while ((pos = pos->next) !=  &cdev->configs) {
>  		c = list_entry(pos, typeof(*c), list);
>  
> -		/* skip OS Descriptors config which is handled separately */
> -		if (c == cdev->os_desc_config)
> -			continue;
> -
> -check_config:

This feels wrong, are you sure that this code isn't here for a reason?
How did you test this?

thanks,

greg k-h