linux-kernel - RE: [LINUX PATCH] usb: xhci: Add toggle cycle bit for the last seg trb when cached ring is used

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Date:   Thu, 1 Jun 2017 16:03:37 +0000
From:   Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Anirudha Sarangi" <anirudh@...inx.com>
Subject: RE: [LINUX PATCH] usb: xhci: Add toggle cycle bit for the last seg
 trb when cached ring is used

HI Mathias,

>-----Original Message-----
>From: Mathias Nyman [mailto:mathias.nyman@...ux.intel.com]
>Sent: Thursday, June 01, 2017 6:51 PM
>To: Anurag Kumar Vulisha <anuragku@...inx.com>; mathias.nyman@...el.com;
>gregkh@...uxfoundation.org
>Cc: linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org; Anirudha Sarangi
><anirudh@...inx.com>; Anurag Kumar Vulisha <anuragku@...inx.com>
>Subject: Re: [LINUX PATCH] usb: xhci: Add toggle cycle bit for the last seg trb
>when cached ring is used
>
>On 31.05.2017 16:41, Anurag Kumar Vulisha wrote:
>> At present USB 2.0 cameras fail to play when run for 2nd time or greater.
>> This issue occurs only when previous endpoint cached ring is used
>> instead of allocating a new endpoint ring. The root cause of the
>> problem narrows down to the Toggle bit, which is not getting set on
>> the last trb of the cached ring last segment. When the controller
>> fetches the last link trb with no toggle bit set, abnormal behaviour is generated.
>> This patch solves that problem by adding the TOGGLE bit for the last
>> trb of the last segment of the cached ring.
>>
>> Signed-off-by: Anurag Kumar Vulisha <anuragku@...inx.com>
>
>Thanks, nice catch.
>
>I'm thinking about removing the whole endpoint ring caching instead.
>
>We are using more memory by caching the rings instead of freeing them,
>especially as we always try to allocate a new ring and only use the cached ones
>when we fail to allocate a new ring.
>
>Would you be willing to test a patch that removes the ring cache completely with
>your setup?
>

Thanks for reviewing the patch. I completely agree with you. But I think instead of
completely removing the cached ring , can we  modify the code to use cached ring
and try to allocate new ep ring on failure to get cached ring. I have previously sent
the patch for doing this https://lkml.org/lkml/2017/2/22/336
But anyways I am ready to test the changes with my platform. Please correct me
if I am wrong

Thanks,
Anurag Kumar Vulisha
 
>Thanks
>Mathias
>