Re: [PATCH v2 1/1] usb: gadget: f_fs: Add support for SuperSpeed Mode

[Felipe Balbi <balbi@ti.com>]

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Hi,

(please avoid top-posting)

On Tue, Sep 24, 2013 at 03:00:20PM +0530, Manu Gautam wrote:
> Hi Felipe,
> 
> I wanted to mention one point with respect to this patch: Below
> changes in the functionfs.h to add ss_count (super speed descriptors
> count) in desc_header (which is passed from userspace) make the driver
> incompatible with existing userspace applications compiled against old
> header file. Let me know if that is acceptable.  We are using this
> driver with Android for adbd (android debug bridge) and these changes
> are required to support adb over Super Speed controllers e.g. DWC3
> along with changed in adbd to pass SS EP and companion descriptors.

Good you mentioned, it saves me the trouble of reviewing this patch :-)

It's not acceptable to break userspace ABI at all. If you want
SuperSpeed support on function fs, we need to figure out a way to do so
without breaking userspace.

This might mean adding a separate userspace interface to be used with
superspeed. While at that, we might want to add a few bytes of reserved,
unused space in our structures for situations where we need to add more
data into it, just to make it slightly future proof.

-- 
balbi

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