linux-kernel - Re: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support

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Date:	Mon, 7 Jul 2014 11:58:43 +0530
From:	sundeep subbaraya <sundeep.lkml@...il.com>
To:	"balbi@...com" <balbi@...com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Subbaraya Sundeep Bhatta <subbaraya.sundeep.bhatta@...inx.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Michal Simek <michals@...inx.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Subbaraya Sundeep Bhatta <sbhatta@...inx.com>
Subject: Re: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support

Hi Felipe,

On Wed, Jul 2, 2014 at 10:16 PM, Felipe Balbi <balbi@...com> wrote:
> Hi,
>
> On Sun, May 25, 2014 at 11:10:30PM +0530, sundeep subbaraya wrote:
>> Hi Felipe,
>>
>> Please take a look at below about how this IP works:
>>
>> IN:
>>       req.buf ---> DMA (transfers from ddr to IP buffer, raise DMA
>> done interrupt and set Buffer ready to transfer data to Host)---->Host
>> PC
>>   buffer sent interrupt
>>
>> OUT:
>>      Host PC--->buffer ready interrupt--->DMA (transfer from IP buffer
>> to DDR,DMA done interrupt, set Buffer ready to receive next data from
>> Host)-->req.buf
>>
>> I written logic to call completion in DMA done handler because it
>> works for both IN and OUT eps. But I see significant performance
>> degradation (by copying a file to mass storage gadget). DMA can handle
>> unaligned address too but it has ep max limit (say 512 for bulk).
>> Hence it is SW job to split packets and to drive DMA till req.length
>> completes. I feel polling for a while is faster than switching between
>> interrupt handler back and forth rapidly. Moreover, DMA may or may not
>> be present in IP based on user configuration at design time.
>>
>> I fixed all other comments expect this one if you do not agree for
>> polling then I may have to create threads and do this stuff. What do
>> you suggest?
>
> Can you resend your driver so we can review again everything you have
> fixed ? I guess you have no other way... polling it is.

Sure. I will resend the driver.

Thanks,
Sundeep.B.S.

>
> cheers
>
> --
> balbi
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