netdev - Re: [PATCH] can: xilinx_can: add support for RX timestamps on Zynq

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Message-ID: <20220718104955.nrlbfnqyhgmnkkey@pengutronix.de>
Date:   Mon, 18 Jul 2022 12:49:55 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Matej Vasilevski <matej.vasilevski@...nam.cz>,
        Michal Simek <michal.simek@...inx.com>
Cc:     Appana Durga Kedareswara rao <appana.durga.rao@...inx.com>,
        Naga Sureshkumar Relli <naga.sureshkumar.relli@...inx.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        Martin Jerabek <martin.jerabek01@...il.com>
Subject: Re: [PATCH] can: xilinx_can: add support for RX timestamps on Zynq

I've added Michal Simek on into the loop.

Michal can you figure out if there's an undocumented register to read
the free running time stamp counter of the xilinx_can IP core?

On 18.07.2022 12:40:03, Matej Vasilevski wrote:
> On Mon, Jul 18, 2022 at 10:33:12AM +0200, Marc Kleine-Budde wrote:
> > On 16.07.2022 14:04:09, Matej Vasilevski wrote:
> > > This patch adds support for hardware RX timestamps from Xilinx Zynq CAN
> > > controllers. The timestamp is calculated against a timepoint reference
> > > stored when the first CAN message is received.
> > > 
> > > When CAN bus traffic does not contain long idle pauses (so that
> > > the clocks would drift by a multiple of the counter rollover time),
> > > then the hardware timestamps provide precise relative time between
> > > received messages. This can be used e.g. for latency testing.
> > 
> > Please make use of the existing cyclecounter/timecounter framework. Is
> > there a way to read the current time from a register? If so, please
> > setup a worker that does that regularly.
> > 
> > Have a look at the mcp251xfd driver as an example:
> > 
> > https://elixir.bootlin.com/linux/latest/source/drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c
> 
> Hi Marc,
> 
> as Pavel have said, the counter register isn't readable.

Some HW designer successfully ticked the mark [x] HW time stamp support!
But haven't thought on how to use this. No Overflow IRQ and no
possibility to read the free running timer. :/

> I'll try to fit the timecounter/cyclecounter framework and send a v2
> patch if it works well. Thanks for the suggestion, it didn't occur to me
> that I can use it in this case as well.

Maybe it's possible to add the ktimestamp based overflow calculation
there, too.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
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