linux-kernel - Re: [PATCH v9 4/5] xhci: mediatek: support MTK xHCI host controller

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Date:	Mon, 19 Oct 2015 14:25:49 +0300
From:	Mathias Nyman <mathias.nyman@...el.com>
To:	chunfeng yun <chunfeng.yun@...iatek.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>
CC:	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Felipe Balbi <balbi@...com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Roger Quadros <rogerq@...com>, linux-usb@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,
	John Crispin <blogic@...nwrt.org>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v9 4/5] xhci: mediatek: support MTK xHCI host controller

>>
>> So basically we are trying to use as many microframes as possible with as few packets
>> per microframe as possible.
>>
>> Did I understand this correctly?
> Yes, you are right.
>
>> How will devices react if they expect to get 16 packets every 16th microframe,
>> but they get one packet every microframe instead?
> I think that the synchronous endpoint must specify its period by
> bInterval, but can't specify how data should be transfered during the
> period by the host, and it just only receives data passively. So the
> device can receive data correctly in the case(bInterval is 5).
>
> quote from usb3_r1.0 section4.4.8 Isochronous Transfers:
> "The host can request data from the device or send data to the device at
> any time during the service interval for a particular endpoint on that
> device"
>

As I understand the 4.4.8 section it just means the device can't assume a fixed
time interval between transfers, meaning that the host can use the last microframe
in one esit and the first microframe in the next esit, but still only use 1 microframe
per esit.

Section 8.12.6.1 describes how a 11 packet isoc transfer is allowed to be split
to 1 burst of 11 packets, 2 burst (8 + 3),  3 burst (4+4+3) 6 bursts (2+2+2+2+2+1) or
11 bursts of 1. These are however all within the same microframe. Splitting the
transfer into several microframes in a esit kind of makes the whole interval concept pointless.

-Mathias



  

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