linux-kernel - Re: [PATCH v2 4/5] USB: gadget: f

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Message-ID: <20201130091259.GB31406@jackp-linux.qualcomm.com>
Date:   Mon, 30 Nov 2020 01:13:00 -0800
From:   Jack Pham <jackp@...eaurora.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     balbi@...nel.org, peter.chen@....com, willmcvicker@...gle.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        "taehyun.cho" <taehyun.cho@...sung.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] USB: gadget: f_fs: add SuperSpeed Plus support

On Fri, Nov 27, 2020 at 03:05:58PM +0100, Greg Kroah-Hartman wrote:
> From: "taehyun.cho" <taehyun.cho@...sung.com>
> 
> Setup the descriptors for SuperSpeed Plus for f_fs. This allows the
> gadget to work properly without crashing at SuperSpeed rates.
> 
> Cc: Felipe Balbi <balbi@...nel.org>
> Cc: stable <stable@...r.kernel.org>
> Signed-off-by: taehyun.cho <taehyun.cho@...sung.com>
> Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> Reviewed-by: Peter Chen <peter.chen@....com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/usb/gadget/function/f_fs.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 046f770a76da..a34a7c96a1ab 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -1327,6 +1327,7 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
>  		struct usb_endpoint_descriptor *desc;
>  
>  		switch (epfile->ffs->gadget->speed) {
> +		case USB_SPEED_SUPER_PLUS:
>  		case USB_SPEED_SUPER:
>  			desc_idx = 2;
>  			break;
> @@ -3222,6 +3223,10 @@ static int _ffs_func_bind(struct usb_configuration *c,
>  	func->function.os_desc_n =
>  		c->cdev->use_os_string ? ffs->interfaces_count : 0;
>  
> +	if (likely(super)) {
> +		func->function.ssp_descriptors =
> +			usb_copy_descriptors(func->function.ss_descriptors);
> +	}
>  	/* And we're done */
>  	ffs_event_add(ffs, FUNCTIONFS_BIND);
>  	return 0;
> -- 

Hi Greg,

FWIW I had sent a very similar patch[1] a while back (twice in fact)
but got no response about it. Looks like Taehyun's patch already went
through Google for this, I assume it must be working on their Android
kernels so I've no problem with you or Felipe taking this instead.

Only one difference with my patch though is mine additionally clears the
func->function.ssp_descriptors member to NULL upon ffs_func_unbind() as
otherwise it could lead to a dangling reference in case the function is
re-bound and userspace does not issue SS descriptors the next time.
Realistically I don't think that's possible, except maybe when fuzzing?

[1] https://patchwork.kernel.org/project/linux-usb/patch/20201027230731.9073-1-jackp@codeaurora.org/

Jack
-- 
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project