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

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Date:	Thu, 08 Oct 2015 16:05:00 +0300
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	Daniel Thompson <daniel.thompson@...aro.org>,
	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 08.10.2015 15:28, Daniel Thompson wrote:
> 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;

Both will work, but I'd prefer this solution as well.

-Mathias

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