netdev - Re: [PATCH V4 3/3] can: m_can: add missing message RAM initialization

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Message-ID: <20141107102130.GA7309@shlinux1.ap.freescale.net>
Date:	Fri, 7 Nov 2014 18:21:35 +0800
From:	Dong Aisheng <b29396@...escale.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
CC:	<linux-can@...r.kernel.org>, <wg@...ndegger.com>,
	<varkabhadram@...il.com>, <netdev@...r.kernel.org>,
	<socketcan@...tkopp.net>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V4 3/3] can: m_can: add missing message RAM
 initialization

On Fri, Nov 07, 2014 at 11:30:38AM +0100, Marc Kleine-Budde wrote:
> On 11/07/2014 09:45 AM, Dong Aisheng wrote:
> > The M_CAN message RAM is usually equipped with a parity or ECC functionality.
> > But RAM cells suffer a hardware reset and can therefore hold arbitrary
> > content at startup - including parity and/or ECC bits.
> > 
> > To prevent the M_CAN controller detecting checksum errors when reading
> > potentially uninitialized TX message RAM content to transmit CAN
> > frames the TX message RAM has to be written with (any kind of) initial
> > data.
> > 
> > Signed-off-by: Dong Aisheng <b29396@...escale.com>
> > ---
> > ChangeLog:
> > v3-v4:
> >  * initialize the entire Message RAM in use instead of only 8 bytes
> >    since this is a valid and needed initialization process.
> >    Patch title also changed.
> > ---
> >  drivers/net/can/m_can/m_can.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> > index eee1533..de742d0 100644
> > --- a/drivers/net/can/m_can/m_can.c
> > +++ b/drivers/net/can/m_can/m_can.c
> > @@ -1114,7 +1114,7 @@ static int m_can_of_parse_mram(struct platform_device *pdev,
> >  	struct resource *res;
> >  	void __iomem *addr;
> >  	u32 out_val[MRAM_CFG_LEN];
> > -	int ret;
> > +	int i, start, end, ret;
> >  
> >  	/* message ram could be shared */
> >  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "message_ram");
> > @@ -1165,6 +1165,15 @@ static int m_can_of_parse_mram(struct platform_device *pdev,
> >  		priv->mcfg[MRAM_TXE].off, priv->mcfg[MRAM_TXE].num,
> >  		priv->mcfg[MRAM_TXB].off, priv->mcfg[MRAM_TXB].num);
> >  
> > +	/* initialize the entire Message RAM in use to avoid possible
> > +	 * ECC/parity checksum errors when reading an uninitialized buffer
> > +	 */
> > +	start = priv->mcfg[MRAM_SIDF].off;
> > +	end = priv->mcfg[MRAM_TXB].off +
> > +		priv->mcfg[MRAM_TXB].num * TXB_ELEMENT_SIZE;
> > +	for (i = start; i < end; i += 4)
> > +		writel(0x0, priv->mram_base + i);
> 
> Can we access the mram without turning on the clock?
> 

Yes, we can.
Since it's CPU access, it seems it does not depend on M_CAN clocks.
What i see from M_CAN subsystem block diagram of MX6SX,
it requires CPU clock which should always be enabled.

Regards
Dong Aisheng

> Marc
> 
> -- 
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |
> 


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