linux-kernel - Re: [PATCH v3 06/16] can: m_can: Write transmit header and data in one transaction

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Message-ID: <20230619114642.66sccv36i4sfonny@blmsp>
Date:   Mon, 19 Jun 2023 13:46:42 +0200
From:   Markus Schneider-Pargmann <msp@...libre.com>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Vincent MAILHOL <mailhol.vincent@...adoo.fr>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 06/16] can: m_can: Write transmit header and data in
 one transaction

Hi Simon,

On Thu, Mar 16, 2023 at 10:27:41AM +0100, Simon Horman wrote:
> On Wed, Mar 15, 2023 at 12:05:36PM +0100, Markus Schneider-Pargmann wrote:
> > Combine header and data before writing to the transmit fifo to reduce
> > the overhead for peripheral chips.
> > 
> > Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> 
> Thanks for addressing my comments on v2.
> 
> > ---
> >  drivers/net/can/m_can/m_can.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> > index a5003435802b..35a2332464e5 100644
> > --- a/drivers/net/can/m_can/m_can.c
> > +++ b/drivers/net/can/m_can/m_can.c
> > @@ -1681,6 +1681,8 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
> >  		m_can_write(cdev, M_CAN_TXBAR, 0x1);
> >  		/* End of xmit function for version 3.0.x */
> >  	} else {
> > +		char buf[TXB_ELEMENT_SIZE];
> > +		u8 len_padded = DIV_ROUND_UP(cf->len, 4);
> >  		/* Transmit routine for version >= v3.1.x */
> >  
> >  		txfqs = m_can_read(cdev, M_CAN_TXFQS);
> > @@ -1720,12 +1722,11 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
> >  		fifo_header.dlc = FIELD_PREP(TX_BUF_MM_MASK, putidx) |
> >  			FIELD_PREP(TX_BUF_DLC_MASK, can_fd_len2dlc(cf->len)) |
> >  			fdflags | TX_BUF_EFC;
> > -		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID, &fifo_header, 2);
> > -		if (err)
> > -			goto out_fail;
> > +		memcpy(buf, &fifo_header, 8);
> > +		memcpy_and_pad(&buf[8], len_padded, &cf->data, cf->len, 0);
> 
> I'm probably missing something obvious here but I'm seeing:
> 
> * len_padded is the number of 4-byte words
> * but the 2nd argument to memcpy_and_pad should be a length in bytes
> * so perhaps it should be: len_padded * 4

Thank you Simon for all the reviews, finally some time to continue on
this:

Thanks for pointing this out. I updated my script used for testing so I
catch something like this the next time. I will be using
TXB_ELEMENT_SIZE - 8 to reflect the buffer size and the 8 byte offset.

Best,
Markus

> 
> >  
> > -		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_DATA,
> > -				       cf->data, DIV_ROUND_UP(cf->len, 4));
> > +		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID,
> > +				       buf, 2 + len_padded);
> 
> This part looks good to me :)
> 
> >  		if (err)
> >  			goto out_fail;
> >  
> > -- 
> > 2.39.2
> >