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Message-ID: <CAMZ6RqK428Pvwrgc=KPKjetZaTC8R55HzypMooOTziM8eMMxHg@mail.gmail.com>
Date: Wed, 16 Oct 2024 23:16:03 +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 Wed. 16 Oct. 2024 at 14:05, Vincent MAILHOL
<mailhol.vincent@...adoo.fr> wrote:
> 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>
> > >> ---
(...)
> > >> +
> > >> + 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?
I received the datasheet from a good samaritan. With this, I was able
to confirm a few things.
1/ Your device can support CAN_CTRLMODE_CC_LEN8_DLC:
This is shown in the datasheet at:
Table 3-52 Definition of the DLC (according to the CAN 2.0 / FD specification)
DLC values 9 to 15 (binary 1001 to 1111) are accepted by the device.
When sending and receiving such frames, can_frame->len is set to 8 and
can_frame->len8_dlc is set to the actual DLC value. Use the
can_cc_dlc2len() and can_get_cc_dlc() helpers for this.
2/ Your device can support CAN_CTRLMODE_TDC_AUTO:
This is documented in the datasheet at:
8.8 TDC and RDC
This will allow the use of higher bitrates (e.g. 4 Mbits/s) in CAN-FD.
You can refer to this commit for an example of how to implement it:
https://git.kernel.org/torvalds/c/1010a8fa9608
3/ Your device can support CAN_CTRLMODE_3_SAMPLES:
This is called triple mode redundancy (TMR) in your datasheet.
4/ Your device can support CAN_CTRLMODE_LISTENONLY:
This is documented in the datasheet at:
3.9.10.2. Listen Only Mode (LOM)
5/ Your device can support CAN_CTRLMODE_ONE_SHOT:
This is documented in the datasheet at:
6.5.3 Single Shot Transmit Trigger
6/ Your device can support CAN_CTRLMODE_BERR_REPORTING:
This is shown in the datasheet at:
Table 3-24 Error Counter Registers RECNT (0xb2) and TECNT (0xb3)
7/ Your device can support CAN_CTRLMODE_PRESUME_ACK:
c.f. the SACK (self acknowledge) register
So your device comes with MANY features. I would like to see those
implemented in your driver. Most of the time, adding a feature just
means writing one value to a register.
Please let me know if any of this is unclear.
Yours sincerely,
Vincent Mailhol
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