netdev - Re: [PATCH v4 2/3] can: ctucanfd: add HW timestamps to RX and error CAN frames

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Date:   Wed, 21 Sep 2022 09:06:49 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Matej Vasilevski <matej.vasilevski@...nam.cz>
Cc:     Pavel Pisa <pisa@....felk.cvut.cz>,
        Ondrej Ille <ondrej.ille@...il.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 2/3] can: ctucanfd: add HW timestamps to RX and error
 CAN frames

On 15.09.2022 01:39:43, Matej Vasilevski wrote:
[...]

>  	/* Check for big-endianity and set according IO-accessors */
>  	if ((ctucan_read32(priv, CTUCANFD_DEVICE_ID) & 0xFFFF) != CTUCANFD_ID) {
> @@ -1425,6 +1582,49 @@ int ctucan_probe_common(struct device *dev, void __iomem *addr, int irq, unsigne
>  
>  	priv->can.clock.freq = can_clk_rate;
>  
> +	/* Obtain timestamping counter bit size */
> +	timestamp_bit_size = FIELD_GET(REG_ERR_CAPT_TS_BITS,
> +				       ctucan_read32(priv, CTUCANFD_ERR_CAPT));
> +
> +	/* The register value is actually bit_size - 1 */
> +	if (timestamp_bit_size) {
> +		timestamp_bit_size += 1;
> +	} else {
> +		/* For 2.x versions of the IP core, we will assume 64-bit counter
> +		 * if there was a 0 in the register.
> +		 */
> +		u32 version_reg = ctucan_read32(priv, CTUCANFD_DEVICE_ID);
> +		u32 major = FIELD_GET(REG_DEVICE_ID_VER_MAJOR, version_reg);
> +
> +		if (major == 2)
> +			timestamp_bit_size = 64;
> +		else
> +			priv->timestamp_possible = false;
> +	}
> +
> +	/* Setup conversion constants and work delay */
> +	priv->cc.mask = CYCLECOUNTER_MASK(timestamp_bit_size);
> +	if (priv->timestamp_possible) {
> +		u64 max_cycles;
> +		u64 work_delay_ns;
> +		u32 maxsec = min_t(u32, CTUCANFD_MAX_WORK_DELAY_SEC,
> +				   div_u64(priv->cc.mask, timestamp_freq));
> +
> +		priv->cc.read = ctucan_read_timestamp_cc_wrapper;
> +		clocks_calc_mult_shift(&priv->cc.mult, &priv->cc.shift,
> +				       timestamp_freq, NSEC_PER_SEC, maxsec);
> +
> +		/* shortened copy of clocks_calc_max_nsecs() */
> +		max_cycles = div_u64(ULLONG_MAX, priv->cc.mult);
> +		max_cycles = min(max_cycles, priv->cc.mask);
> +		work_delay_ns = clocksource_cyc2ns(max_cycles, priv->cc.mult,
> +						   priv->cc.shift) >> 1;

I just ported the code to another driver with dynamic frequency and
width. I noticed that the shift of 1 is not enough. With 2 it works.

regards,
MArc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |


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