linux-kernel - Re: [PATCH v10 2/6] usb: gadget: configfs: Check USB configuration before adding

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Message-ID: <YMss5tFFBjokk1k6@kroah.com>
Date:   Thu, 17 Jun 2021 13:07:18 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Wesley Cheng <wcheng@...eaurora.org>
Cc:     balbi@...nel.org, robh+dt@...nel.org, agross@...nel.org,
        bjorn.andersson@...aro.org, frowand.list@...il.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        jackp@...eaurora.org, fntoth@...il.com,
        heikki.krogerus@...ux.intel.com, andy.shevchenko@...il.com
Subject: Re: [PATCH v10 2/6] usb: gadget: configfs: Check USB configuration
 before adding

On Thu, Jun 17, 2021 at 02:58:15AM -0700, Wesley Cheng wrote:
> Ensure that the USB gadget is able to support the configuration being
> added based on the number of endpoints required from all interfaces.  This
> is for accounting for any bandwidth or space limitations.
> 
> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
> ---
>  drivers/usb/gadget/configfs.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 15a607c..76b9983 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -1374,6 +1374,7 @@ static int configfs_composite_bind(struct usb_gadget *gadget,
>  		struct usb_function *f;
>  		struct usb_function *tmp;
>  		struct gadget_config_name *cn;
> +		unsigned long ep_map = 0;
>  
>  		if (gadget_is_otg(gadget))
>  			c->descriptors = otg_desc;
> @@ -1403,7 +1404,28 @@ static int configfs_composite_bind(struct usb_gadget *gadget,
>  				list_add(&f->list, &cfg->func_list);
>  				goto err_purge_funcs;
>  			}
> +			if (f->fs_descriptors) {
> +				struct usb_descriptor_header **d;
> +
> +				d = f->fs_descriptors;
> +				for (; *d; ++d) {

With this check, there really is not a need to check for
f->fs_descriptors above in the if statement, right?

> +					struct usb_endpoint_descriptor *ep;
> +					int addr;
> +
> +					if ((*d)->bDescriptorType != USB_DT_ENDPOINT)
> +						continue;
> +
> +					ep = (struct usb_endpoint_descriptor *)*d;
> +					addr = ((ep->bEndpointAddress & 0x80) >> 3) |
> +						(ep->bEndpointAddress & 0x0f);

Don't we have direction macros for this type of check?

> +					set_bit(addr, &ep_map);
> +				}

What is this loop trying to do?  Please document it as I can not figure
it out at all.

thanks,

greg k-h