[RFC 13/13] USB: Disable hub-initiated LPM for comms devices.
tilman at imap.cc
Fri May 18 18:38:41 EDT 2012
Am 17.05.2012 19:31, schrieb Sarah Sharp:
> On Thu, May 17, 2012 at 07:07:32PM +0200, Tilman Schmidt wrote:
>> I follow the argument for class drivers. But this patch also
>> modifies drivers for specific existing USB 2.0 only devices
>> which are unlikely to ever grow USB 3.0 support, such as the
>> Gigaset ISDN driver:
>>> drivers/isdn/gigaset/bas-gigaset.c | 1 +
>>> drivers/isdn/gigaset/usb-gigaset.c | 1 +
> Is there a particular reason why you think that driver is unlikely to
> ever get USB 3.0 support?
Actually, there is. :-)
- The USB devices driven by this driver aren't built anymore.
- Their USB interface design is quite, um, idiosyncratic, and it's
pretty unlikely that anyone will reuse it. (At least I truly hope
no one will.)
- Their successor models have completely different and incompatible
USB interfaces which this driver is unable to handle.
>> What is the interest of setting the disable_hub_initiated_lpm
>> flag for these?
> It's partially to lay the foundation for anyone who wants to make a USB
> 3.0 communications driver in the future. They're likely to start from
> some USB 2.0 class driver, and copy a lot of code. If they notice that
> flag is set in all the USB communications class drivers, they're likely
> to set it as well.
You've got a point there.
> I'm not quite sure where the best place to provide documentation on the
> flag is. I've added the kernel doc comments to the structure, but maybe
> it needs to be documented somewhere in Documentation/usb/?
Documentation/usb/power-management.txt would seem like a natural
place. Although it appears to limit itself to "suspending" in its
first paragraph, it does have a section "xHCI hardware link PM"
at the end already, added by Andiry Xu on 2011-09-23.
Hmmm, that section seems to suggest that LPM exists for USB2, too.
Perhaps I should reconsider my attitude towards your patch.
Tilman Schmidt E-Mail: tilman at imap.cc
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