linux-kernel - Re: [PATCH v5 4/7] can: dev: add can_tdc_get_relative

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Date:   Mon, 16 Aug 2021 13:27:03 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc:     linux-can@...r.kernel.org,
        Stefan Mätje <Stefan.Maetje@....eu>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] can: dev: add can_tdc_get_relative_tdco() helper
 function

On 15.08.2021 12:32:45, Vincent Mailhol wrote:
> struct can_tdc::tdco represents the absolute offset from TDCV. Some
> controllers use instead an offset relative to the Sample Point (SP)
> such that:
> | SSP = TDCV + absolute TDCO
> |     = TDCV + SP + relative TDCO
> 
> Consequently:
> | relative TDCO = absolute TDCO - SP
> 
> The function can_tdc_get_relative_tdco() allow to retrieve this
> relative TDCO value.
> 
> CC: Stefan Mätje <Stefan.Maetje@....eu>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> ---
>  include/linux/can/dev.h | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
> index 0be982fd22fb..fa75e29182a3 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -93,6 +93,35 @@ static inline bool can_tdc_is_enabled(const struct can_priv *priv)
>  	return !!(priv->ctrlmode & CAN_CTRLMODE_TDC_MASK);
>  }
>  
> +/*
> + * can_get_relative_tdco() - TDCO relative to the sample point
> + *
> + * struct can_tdc::tdco represents the absolute offset from TDCV. Some
> + * controllers use instead an offset relative to the Sample Point (SP)
> + * such that:
> + *
> + * SSP = TDCV + absolute TDCO
> + *     = TDCV + SP + relative TDCO
> + *
> + * -+----------- one bit ----------+-- TX pin
> + *  |<--- Sample Point --->|
> + *
> + *                         --+----------- one bit ----------+-- RX pin
> + *  |<-------- TDCV -------->|
> + *                           |<------------------------>| absolute TDCO
> + *                           |<--- Sample Point --->|
> + *                           |                      |<->| relative TDCO
> + *  |<------------- Secondary Sample Point ------------>|
> + */
> +static inline s32 can_get_relative_tdco(const struct can_priv *priv)
> +{
> +	const struct can_bittiming *dbt = &priv->data_bittiming;
> +	s32 sample_point_in_tc =  (CAN_SYNC_SEG + dbt->prop_seg +
                                ^^

Only one space. I'll fix the while applying.

> +				   dbt->phase_seg1) * dbt->brp;
> +
> +	return (s32)priv->tdc.tdco - sample_point_in_tc;
> +}
> +
>  /* helper to define static CAN controller features at device creation time */
>  static inline void can_set_static_ctrlmode(struct net_device *dev,
>  					   u32 static_mode)

Marc

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

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