linux-kernel - Re: [PATCH v3 6/8] usb: dwc2: host: Assume all devices are on one single

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Date:	Thu, 19 Nov 2015 13:20:23 -0600
From:	Felipe Balbi <balbi@...com>
To:	Doug Anderson <dianders@...omium.org>
CC:	John Youn <John.Youn@...opsys.com>, Yunzhi Li <lyz@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Julius Werner <jwerner@...omium.org>,
	"Herrero, Gregory" <gregory.herrero@...el.com>,
	"Kaukab, Yousaf" <yousaf.kaukab@...el.com>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Ming Lei <ming.lei@...onical.com>,
	John Youn <johnyoun@...opsys.com>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/8] usb: dwc2: host: Assume all devices are on one single_tt hub


Hi,

Doug Anderson <dianders@...omium.org> writes:
>> Douglas Anderson <dianders@...omium.org> writes:
>>> Until we have logic to determine which devices share the same TT let's
>>> add logic to assume that all devices on a given dwc2 controller are on
>>> one single_tt hub.  This is better than the previous code that assumed
>>> that all devices were on one multi_tt hub, since single_tt hubs
>>> appear (in my experience) to be much more common and any schedule that
>>> would work on a single_tt hub will also work on a multi_tt hub.  This
>>> will prevent more than 8 total low/full speed devices to be on the bus
>>> at one time, but that's a reasonable restriction until we've made things
>>> smarter.
>>>
>>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>>> ---
>>> Changes in v3:
>>> - Assuming single_tt is new for v3; not terribly well tested (yet).
>>>
>>> Changes in v2: None
>>>
>>>  drivers/usb/dwc2/core.h      |  1 +
>>>  drivers/usb/dwc2/hcd_queue.c | 40 +++++++++++++++++++++++++++++++++++++++-
>>>  2 files changed, 40 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
>>> index 567ee2c9e69f..09aa2b5ae29e 100644
>>> --- a/drivers/usb/dwc2/core.h
>>> +++ b/drivers/usb/dwc2/core.h
>>> @@ -782,6 +782,7 @@ struct dwc2_hsotg {
>>>       u16 periodic_usecs;
>>>       unsigned long periodic_bitmap[DIV_ROUND_UP(TOTAL_PERIODIC_USEC,
>>>                                                  BITS_PER_LONG)];
>>> +     bool has_split[8];
>>
>> why don't you use a u8 instead then just set each bit for each
>> "has_split" you need to take care of. This array is kinda ugly.
>
> Let's actually drop this patch completely.  Julius and I sat down and
> he talked me through things, and with my current understanding the
> current microframe scheduler in dwc2 is broken enough that small
> little band-aids like this will do little more than just push the
> problems around.
>
> I'm a good portion of the way through a better microframe scheduler.
> I have no doubt that it won't be perfect, but hopefully it will at
> least be based in reality...
>
> My latest thinking on the patches in this series:
>
> 1. usb: dwc2: rockchip: Make the max_transfer_size automatic
>
> I'll probably separate this out into its own patch so I can stop
> sending it as part of this series.  ...or if someone wanted to land it
> then I won't bother.
>
>
> 2. usb: dwc2: host: Get aligned DMA in a more supported way
>
> Still can land any time and has good benefits.  I believe that I can't
> separate this because it will cause conflicts with scheduler patches.
>
>
> 3. usb: dwc2: host: Add scheduler tracing
>
> Would be nice to land.
>
>
> 4. usb: dwc2: host: Rewrite the microframe scheduler
> 5. usb: dwc2: host: Keep track of and use our scheduled microframe
> 6. usb: dwc2: host: Assume all devices are on one single_tt hub
>
> Please drop patches 4-6 right now.
>
>
> 7. usb: dwc2: host: Add a delay before releasing periodic bandwidth
> 8. usb: dwc2: host: Giveback URB in tasklet context

if you can, it's best to send a new series with the changes. This makes
mine and John's life a lot easier :-)

> I'll probably move these back up in the series (like in v2) and put
> microframe rewrite atop them.  With my current understanding the
> scheduling is so broken today that the concerns Alan brought up can
> wait until we have a proper scheduler to be addressed.  In the
> meantime getting the huge boost in interrupt speed will help with
> dwc2's correctness (and performance) because it means we're much less
> likely to miss SOF interrupts.
>
> If anyone has any review time, giving a review to v2 of these patches
> would be helpful.  Otherwise I'll double check that v2 still looks
> good with my current understanding and eventually post them again.

That would have to be someone experienced with that IP. I don't even
have docs :-)

-- 
balbi

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