linux-kernel - Re: [PATCH v2 2/6] can: esd_usb: Replace initializer macros used for struct can_bittiming

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Date:   Sun, 21 May 2023 18:16:17 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Frank Jungclaus <frank.jungclaus@....eu>
Cc:     linux-can@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Stefan Mätje <stefan.maetje@....eu>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] can: esd_usb: Replace initializer macros used for
 struct can_bittiming_const

Thanks for the patch.

On Sat. 20 May 2023 at 04:57, Frank Jungclaus <frank.jungclaus@....eu> wrote:
> Replace the macros used to initialize the members of struct
> can_bittiming_const with direct values. Then also use those struct
> members to do the calculations in esd_usb2_set_bittiming().
>
> Link: https://lore.kernel.org/all/CAMZ6RqLaDNy-fZ2G0+QMhUEckkXLL+ZyELVSDFmqpd++aBzZQg@mail.gmail.com/
> Suggested-by: Vincent MAILHOL <mailhol.vincent@...adoo.fr>
> Signed-off-by: Frank Jungclaus <frank.jungclaus@....eu>
> ---
>  drivers/net/can/usb/esd_usb.c | 33 +++++++++++++--------------------
>  1 file changed, 13 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/net/can/usb/esd_usb.c b/drivers/net/can/usb/esd_usb.c
> index 32354cfdf151..2eecf352ec47 100644
> --- a/drivers/net/can/usb/esd_usb.c
> +++ b/drivers/net/can/usb/esd_usb.c
> @@ -60,18 +60,10 @@ MODULE_LICENSE("GPL v2");
>  #define ESD_USB_NO_BAUDRATE    GENMASK(30, 0) /* bit rate unconfigured */
>
>  /* bit timing CAN-USB/2 */
> -#define ESD_USB2_TSEG1_MIN     1
> -#define ESD_USB2_TSEG1_MAX     16
>  #define ESD_USB2_TSEG1_SHIFT   16
> -#define ESD_USB2_TSEG2_MIN     1
> -#define ESD_USB2_TSEG2_MAX     8
>  #define ESD_USB2_TSEG2_SHIFT   20
> -#define ESD_USB2_SJW_MAX       4
>  #define ESD_USB2_SJW_SHIFT     14
>  #define ESD_USBM_SJW_SHIFT     24
> -#define ESD_USB2_BRP_MIN       1
> -#define ESD_USB2_BRP_MAX       1024
> -#define ESD_USB2_BRP_INC       1
>  #define ESD_USB2_3_SAMPLES     BIT(23)
>
>  /* esd IDADD message */
> @@ -909,19 +901,20 @@ static const struct ethtool_ops esd_usb_ethtool_ops = {
>
>  static const struct can_bittiming_const esd_usb2_bittiming_const = {
>         .name = "esd_usb2",
> -       .tseg1_min = ESD_USB2_TSEG1_MIN,
> -       .tseg1_max = ESD_USB2_TSEG1_MAX,
> -       .tseg2_min = ESD_USB2_TSEG2_MIN,
> -       .tseg2_max = ESD_USB2_TSEG2_MAX,
> -       .sjw_max = ESD_USB2_SJW_MAX,
> -       .brp_min = ESD_USB2_BRP_MIN,
> -       .brp_max = ESD_USB2_BRP_MAX,
> -       .brp_inc = ESD_USB2_BRP_INC,
> +       .tseg1_min = 1,
> +       .tseg1_max = 16,
> +       .tseg2_min = 1,
> +       .tseg2_max = 8,
> +       .sjw_max = 4,
> +       .brp_min = 1,
> +       .brp_max = 1024,
> +       .brp_inc = 1,
>  };
>
>  static int esd_usb2_set_bittiming(struct net_device *netdev)
>  {
>         struct esd_usb_net_priv *priv = netdev_priv(netdev);
> +       const struct can_bittiming_const *btc = priv->can.bittiming_const;

I initially suggested doing:

          const struct can_bittiming_const *btc = priv->can.bittiming_const;

But now that I think again about it, doing:

          const struct can_bittiming_const *btc = &esd_usb2_bittiming_const;

is slightly better as it will allow the compiler to fold the integer
constant expressions such as btc->brp_max - 1. The compiler is not
smart enough to figure out what values are held in
priv->can.bittiming_const at compile time.

Sorry for not figuring this the first time.

>         struct can_bittiming *bt = &priv->can.bittiming;
>         union esd_usb_msg *msg;
>         int err;
> @@ -932,7 +925,7 @@ static int esd_usb2_set_bittiming(struct net_device *netdev)
>         if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
>                 canbtr |= ESD_USB_LOM;
>
> -       canbtr |= (bt->brp - 1) & (ESD_USB2_BRP_MAX - 1);
> +       canbtr |= (bt->brp - 1) & (btc->brp_max - 1);
>
>         if (le16_to_cpu(priv->usb->udev->descriptor.idProduct) ==
>             USB_CANUSBM_PRODUCT_ID)
> @@ -940,12 +933,12 @@ static int esd_usb2_set_bittiming(struct net_device *netdev)
>         else
>                 sjw_shift = ESD_USB2_SJW_SHIFT;
>
> -       canbtr |= ((bt->sjw - 1) & (ESD_USB2_SJW_MAX - 1))
> +       canbtr |= ((bt->sjw - 1) & (btc->sjw_max - 1))
>                 << sjw_shift;
>         canbtr |= ((bt->prop_seg + bt->phase_seg1 - 1)
> -                  & (ESD_USB2_TSEG1_MAX - 1))
> +                  & (btc->tseg1_max - 1))
>                 << ESD_USB2_TSEG1_SHIFT;
> -       canbtr |= ((bt->phase_seg2 - 1) & (ESD_USB2_TSEG2_MAX - 1))
> +       canbtr |= ((bt->phase_seg2 - 1) & (btc->tseg2_max - 1))
>                 << ESD_USB2_TSEG2_SHIFT;
>         if (priv->can.ctrlmode & CAN_CTRLMODE_3_SAMPLES)
>                 canbtr |= ESD_USB2_3_SAMPLES;
> --
> 2.25.1
>