linux-kernel - Re: [PATCH USB v3 3/5] usb: raw-gadget: fix gadget endpoint selection

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Date:   Sat, 09 May 2020 11:00:04 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH USB v3 3/5] usb: raw-gadget: fix gadget endpoint selection

Andrey Konovalov <andreyknvl@...gle.com> writes:

> Currently automatic gadget endpoint selection based on required features
> doesn't work. Raw Gadget tries iterating over the list of available
> endpoints and finding one that has the right direction and transfer type.
> Unfortunately selecting arbitrary gadget endpoints (even if they satisfy
> feature requirements) doesn't work, as (depending on the UDC driver) they
> might have fixed addresses, and one also needs to provide matching
> endpoint addresses in the descriptors sent to the host.
>
> The composite framework deals with this by assigning endpoint addresses
> in usb_ep_autoconfig() before enumeration starts. This approach won't work
> with Raw Gadget as the endpoints are supposed to be enabled after a
> set_configuration/set_interface request from the host, so it's too late to
> patch the endpoint descriptors that had already been sent to the host.
>
> For Raw Gadget we take another approach. Similarly to GadgetFS, we allow
> the user to make the decision as to which gadget endpoints to use.
>
> This patch adds another Raw Gadget ioctl USB_RAW_IOCTL_EPS_INFO that
> exposes information about all non-control endpoints that a currently
> connected UDC has. This information includes endpoints addresses, as well
> as their capabilities and limits to allow the user to choose the most
> fitting gadget endpoint.
>
> The USB_RAW_IOCTL_EP_ENABLE ioctl is updated to use the proper endpoint
> validation routine usb_gadget_ep_match_desc().
>
> These changes affect the portability of the gadgets that use Raw Gadget
> when running on different UDCs. Nevertheless, as long as the user relies
> on the information provided by USB_RAW_IOCTL_EPS_INFO to dynamically
> choose endpoint addresses, UDC-agnostic gadgets can still be written with
> Raw Gadget.
>
> Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---

you're adding a new IOCTL, how is this a fix?

-- 
balbi

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