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

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Message-ID: <5616616D.3080205@linaro.org>
Date:	Thu, 8 Oct 2015 13:28:29 +0100
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	chunfeng yun <chunfeng.yun@...iatek.com>
Cc:	Mathias Nyman <mathias.nyman@...el.com>,
	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

On 08/10/15 13:05, chunfeng yun wrote:
> Hi,
> On Thu, 2015-10-01 at 12:44 +0100, Daniel Thompson wrote:
>> On 29/09/15 04:01, Chunfeng Yun wrote:
>>> There some vendor quirks for MTK xhci host controller:
>>> 1. It defines some extra SW scheduling parameters for HW
>>>     to minimize the scheduling effort for synchronous and
>>>     interrupt endpoints. The parameters are put into reseved
>>>     DWs of slot context and endpoint context.
>>> 2. Its IMODI unit for Interrupter Moderation register is
>>>     8 times as much as that defined in xHCI spec.
>>> 3. Its TDS in  Normal TRB defines a number of packets that
>>>     remains to be transferred for a TD after processing all
>>>     Max packets in all previous TRBs.
>>>
>>> Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
>>
>> I've done some basic soak tests, both with a directly attached USB3 HDD
>> and, given the extra code to manage isochronous xfer, also with a hub,
>> disc and two audio interfaces.
>>
>> Tested-by: Daniel Thompson <daniel.thompson@...aro.org>
>>
>>
>>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
>>> index 57f40a1..243f696 100644
>>> --- a/drivers/usb/host/xhci-ring.c
>>> +++ b/drivers/usb/host/xhci-ring.c
>>> @@ -68,6 +68,7 @@
>>>    #include <linux/slab.h>
>>>    #include "xhci.h"
>>>    #include "xhci-trace.h"
>>> +#include "xhci-mtk.h"
>>>
>>>    /*
>>>     * Returns zero if the TRB isn't in this segment, otherwise it returns the DMA
>>> @@ -3044,18 +3045,27 @@ static u32 xhci_td_remainder(struct xhci_hcd *xhci, int transferred,
>>>    			      struct urb *urb, unsigned int num_trbs_left)
>>>    {
>>>    	u32 maxp, total_packet_count;
>>> +	u32 skip_current_trb = 0;
>>
>> A bit of a nitpick but why do we need skip_current_trb? Testing
>> (xhci->quirks & XHCI_MTK_HOST) twice would make what the code does, and
>> why, more obvious.
>>
> I am not sure which way it is better, so add variable of
> skip_current_trb to reduce test times.

I can't imagine either approach impacts performance. However introducing 
skip_current_trb makes the flow of the branches harder to follow.

The first branch was a version check and can remain so; we only need to 
do something special with the quirks because the MTK controller is 0.97 
but with a few bits added:

     /* MTK xHCI is mostly 0.97 but contains some features from 1.0 */
     if (xhci->hci_version < 0x100 && !(xhci->quirks & XHCI_MTK_HOST))
	    return ...

Setting trb_buff_len to zero is accommodating a quirk and this is 
clearer when we have:

     /* for MTK xHCI, TD size doesn't include this TRB */
     if (xhci->quirks & XHCI_MTK_HOST)
	    trb_buff_len = 0;


>> Anyhow with that looked at, and the caveat that I'm not much of USB
>> expert, you're welcome to add my Reviewed-by: to v10.
>>
>
> Thanks a lot

No worries.

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