linux-kernel - Re: [PATCH v2 3/4] can: Add driver for CAST CAN Bus Controller

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Message-ID: <CAMZ6RqLvzvttbCMFbZiY9v=nGcH+O3EV91c+x7GxTbkKhdTcwg@mail.gmail.com>
Date: Wed, 16 Oct 2024 14:05:57 +0900
From: Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To: Hal Feng <hal.feng@...ux.starfivetech.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Marc Kleine-Budde <mkl@...gutronix.de>, 
	"David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Palmer Dabbelt <palmer@...belt.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Emil Renner Berthing <emil.renner.berthing@...onical.com>, 
	William Qiu <william.qiu@...rfivetech.com>, devicetree@...r.kernel.org, 
	linux-can@...r.kernel.org, netdev@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Hal Feng <hal.feng@...rfivetech.com>
Subject: Re: [PATCH v2 3/4] can: Add driver for CAST CAN Bus Controller

On Tue. 15 Oct. 2024 at 18:33, Hal Feng <hal.feng@...ux.starfivetech.com> wrote:
> On 9/23/2024 11:41 AM, Vincent MAILHOL wrote:
> > Hi Hal,
> >
> > A few more comments on top of what Andrew already wrote.
> >
> > On Mon. 23 Sep. 2024 at 00:09, Hal Feng <hal.feng@...rfivetech.com> wrote:
> >> From: William Qiu <william.qiu@...rfivetech.com>
> >>
> >> Add driver for CAST CAN Bus Controller used on
> >> StarFive JH7110 SoC.
> >>
> >> Signed-off-by: William Qiu <william.qiu@...rfivetech.com>
> >> Co-developed-by: Hal Feng <hal.feng@...rfivetech.com>
> >> Signed-off-by: Hal Feng <hal.feng@...rfivetech.com>
> >> ---

(...)

> >> +       stats->rx_packets++;
> >> +       netif_receive_skb(skb);
> >> +
> >> +       return 1;
> >
> > Why return 1 on success and 0 on failure? The convention in the kernel
> > is that 0 means success. If you really want to keep 0 for failure, at
> > least make this return boolean true or boolean false, but overall, try
> > to follow the return conventions.
>
> The return value here represents the number of successfully received packets.
> It is used in ccan_rx_poll() for counting the number of successfully
> received packets.

Ack. I guess this will become more clear after you implement the queue logic.

(...)

> >> +
> >> +       if (priv->cantype == CAST_CAN_TYPE_CANFD) {
> >> +               priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK | CAN_CTRLMODE_FD;
> >> +               priv->can.data_bittiming_const = &ccan_data_bittiming_const_canfd;
> >> +       } else {
> >> +               priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK;
> >> +       }
> >
> > Nitpick, consider doing this:
> >
> >   priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK;
> >   if (priv->cantype == CAST_CAN_TYPE_CANFD) {
> >           priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD;
> >           priv->can.data_bittiming_const = &ccan_data_bittiming_const_canfd;
> >   }
>
> OK.
>
> >
> > Also, does you hardware support dlc greater than 8 (c.f.
> > CAN_CTRLMODE_CC_LEN8_DLC)?
>
> The class CAN (CC) mode does not support, but the CAN FD mode supports.

So, CAN_CTRLMODE_CC_LEN8_DLC is a Classical CAN feature. Strictly
speaking, this does not exist in CAN FD. Do you mean that only the
CAST_CAN_TYPE_CANFD supports sending Classical CAN frames with a DLC
greater than 8?

If none of the Classical CAN or CAN FD variants of your device is able
to send Classical CAN frames with a DLC greater than 8, then this is
just not supported by your device.

Could you share the datasheet so that I can double check this?

(...)

> Sorry for the late reply. Thank you for your detailed review.

No problem, take your time!


Yours sincerely,
Vincent Mailhol