linux-kernel - Re: [PATCH 3/6] net: ethernet: ti: cpts: add support of cpts HW_TS

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Message-ID: <58eea45f-b8fe-6892-e784-b41638c62fd8@ti.com>
Date:   Thu, 8 Dec 2016 13:04:11 -0600
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Mugunthan V N <mugunthanvnm@...com>,
        Sekhar Nori <nsekhar@...com>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>,
        Murali Karicheri <m-karicheri2@...com>,
        Wingman Kwok <w-kwok2@...com>
Subject: Re: [PATCH 3/6] net: ethernet: ti: cpts: add support of cpts
 HW_TS_PUSH



On 12/03/2016 05:21 PM, Richard Cochran wrote:
> On Mon, Nov 28, 2016 at 05:04:25PM -0600, Grygorii Strashko wrote:
>> This also change overflow polling period when HW_TS_PUSH feature is
>> enabled - overflow check work will be scheduled more often (every
>> 200ms) for proper HW_TS_PUSH events reporting.
> 
> For proper reporting, you should make use of the interrupt.  The small
> fifo (16 iirc) could very well overflow in 200 ms.  The interrupt
> handler should read out the entire fifo at each interrupt.
> 

huh. Seems this is not really good idea, because MISC Irq will be 
triggered for *any* CPTS event and there is no way to enable it just for
HW_TS_PUSH. So, this doesn't work will with current code for RX/TX timestamping
(which uses polling mode). + runtime overhead in net RX/TX caused by 
triggering more interrupts. 

May be, overflow check/polling timeout can be made configurable (module parameter). 

-- 
regards,
-grygorii