From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dong Aisheng Subject: Re: [PATCH 7/7] can: m_can: workaround for transmit data less than 4 bytes Date: Wed, 5 Nov 2014 10:07:40 +0800 Message-ID: <20141105020739.GB18982@shlinux1.ap.freescale.net> References: <1414579527-31100-1-git-send-email-b29396@freescale.com> <1414579527-31100-7-git-send-email-b29396@freescale.com> <5457B1D1.6080301@pengutronix.de> <20141104082505.GA8060@shlinux1.ap.freescale.net> <54589AC8.4010106@pengutronix.de> <20141104092651.GC8060@shlinux1.ap.freescale.net> <5458AB65.7000500@pengutronix.de> <5458D0FA.1040504@hartkopp.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Marc Kleine-Budde , , , , , To: Oliver Hartkopp Return-path: Content-Disposition: inline In-Reply-To: <5458D0FA.1040504@hartkopp.net> Sender: linux-can-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Nov 04, 2014 at 02:13:30PM +0100, Oliver Hartkopp wrote: > > > On 04.11.2014 11:33, Marc Kleine-Budde wrote: > >On 11/04/2014 10:27 AM, Dong Aisheng wrote: > > > >>+ /* We meet an IC issue that we have to write the full 8 > > > >At least on the *insert SoC name here*, an issue with the Message RAM > >was discovered. Sending CAN frames with dlc less than 4 bytes will lead > >to bit errors, when the first 8 bytes of the Message RAM have not been > >initialized (i.e. written to). To work around this issue, the first 8 > >bytes are initialized here. > > Yes. Also put the current IP revision (3.0.x) into the comment. > Did inform the Bosch guys from this issue - or is it already in some errata sheet? > Good idea, will add it. I will try if we can talk Bosch guys about this issue. Regards Dong Aisheng > > > >>+ * bytes (whatever value for the second word) in Message RAM to > >>+ * avoid bit error for transmit data less than 4 bytes at the first > >>+ * time. By initializing the first 8 bytes of tx buffer before using > >>+ * it can avoid such issue. > >>+ */ > >>+ m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(0), 0x0); > >>+ m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(1), 0x0); > >>+ > >> m_can_config_endisable(priv, false); > >> } > > > >Can you trigger the issue when sending CAN-FD frames with dlc > 8 && dlc > >< 64? > > Just a nitpick: > > DLC can just be 0 .. 15 > > and the length (struct canfd_frame.len) can be from 0 .. 64 > > See: > > http://lxr.free-electrons.com/source/include/uapi/linux/can.h#L83 > > That's the reason for all these helpers > > http://lxr.free-electrons.com/source/drivers/net/can/dev.c#L36 > > that hide the evil "DLC" from userspace now and make 'len' a usable > loop variable as we were able to use the former dlc for classic CAN > :-) > > Regards, > Oliver >