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Date:   Fri, 6 Aug 2021 11:36:58 +0200
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Dario Binacchi <dariobin@libero.it>
Cc:     linux-kernel@vger.kernel.org,
        Gianluca Falavigna <gianluca.falavigna@inwind.it>,
        Andrew Lunn <andrew@lunn.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        Wolfgang Grandegger <wg@grandegger.com>,
        linux-can@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH v2 4/4] can: c_can: cache frames to operate as a true FIFO
Message-ID: <20210806093658.rvzw7zycrmyp4msp@pengutronix.de>
References: <20210805201900.23146-1-dariobin@libero.it>
 <20210805201900.23146-5-dariobin@libero.it>
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On 05.08.2021 22:19:00, Dario Binacchi wrote:
> As reported by a comment in the c_can_start_xmit() this was not a FIFO.
> C/D_CAN controller sends out the buffers prioritized so that the lowest
> buffer number wins.
>=20
> What did c_can_start_xmit() do if head was less tail in the tx ring ? It
> waited until all the frames queued in the FIFO was actually transmitted
> by the controller before accepting a new CAN frame to transmit, even if
> the FIFO was not full, to ensure that the messages were transmitted in
> the order in which they were loaded.
>=20
> By storing the frames in the FIFO without requiring its transmission, we
> will be able to use the full size of the FIFO even in cases such as the
> one described above. The transmission interrupt will trigger their
> transmission only when all the messages previously loaded but stored in
> less priority positions of the buffers have been transmitted.
>=20
> Suggested-by: Gianluca Falavigna <gianluca.falavigna@inwind.it>
> Signed-off-by: Dario Binacchi <dariobin@libero.it>

My review from
https://lore.kernel.org/linux-can/20210806092523.hij5ejjq6wecbgfr@pengutron=
ix.de/
applies here, too.

Please use IF_RX in c_can_do_tx(), remove the spin_lock and test. After
applying your series, I'll send a patch that changes IF_RX into IF_NAPI
to avoid any further confusion.

regards,
Marc

--=20
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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