Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751348AbdINFGu (ORCPT ); Thu, 14 Sep 2017 01:06:50 -0400 Received: from lelnx194.ext.ti.com ([198.47.27.80]:52766 "EHLO lelnx194.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbdINFGs (ORCPT ); Thu, 14 Sep 2017 01:06:48 -0400 Subject: Re: [RFC PATCH] can: m_can: Support higher speed CAN-FD bitrates To: Franklin S Cooper Jr , , , , , , , , , References: <20170818193947.27862-1-fcooper@ti.com> <4f8f6b64-b2a2-b9dc-665c-f1c155daf994@ti.com> CC: Wenyou Yang , Dong Aisheng From: Sekhar Nori Message-ID: Date: Thu, 14 Sep 2017 10:36:18 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <4f8f6b64-b2a2-b9dc-665c-f1c155daf994@ti.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3801 Lines: 100 On Thursday 14 September 2017 03:28 AM, Franklin S Cooper Jr wrote: > > > On 08/18/2017 02:39 PM, Franklin S Cooper Jr wrote: >> During test transmitting using CAN-FD at high bitrates (4 Mbps) only >> resulted in errors. Scoping the signals I noticed that only a single bit >> was being transmitted and with a bit more investigation realized the actual >> MCAN IP would go back to initialization mode automatically. >> >> It appears this issue is due to the MCAN needing to use the Transmitter >> Delay Compensation Mode as defined in the MCAN User's Guide. When this >> mode is used the User's Guide indicates that the Transmitter Delay >> Compensation Offset register should be set. The document mentions that this >> register should be set to (1/dbitrate)/2*(Func Clk Freq). >> >> Additional CAN-CIA's "Bit Time Requirements for CAN FD" document indicates >> that this TDC mode is only needed for data bit rates above 2.5 Mbps. >> Therefore, only enable this mode and only set TDCO when the data bit rate >> is above 2.5 Mbps. >> >> Signed-off-by: Franklin S Cooper Jr >> --- >> I'm pretty surprised that this hasn't been implemented already since >> the primary purpose of CAN-FD is to go beyond 1 Mbps and the MCAN IP >> supports up to 10 Mbps. >> >> So it will be nice to get comments from users of this driver to understand >> if they have been able to use CAN-FD beyond 2.5 Mbps without this patch. >> If they haven't what did they do to get around it if they needed higher >> speeds. >> >> Meanwhile I plan on testing this using a more "realistic" CAN bus to insure >> everything still works at 5 Mbps which is the max speed of my CAN >> transceiver. > > ping. Anyone has any thoughts on this? I added Dong who authored the m_can driver and Wenyou who added the only in-kernel user of the driver for any help. Thanks, Sekhar >> >> drivers/net/can/m_can/m_can.c | 24 +++++++++++++++++++++++- >> 1 file changed, 23 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c >> index f4947a7..720e073 100644 >> --- a/drivers/net/can/m_can/m_can.c >> +++ b/drivers/net/can/m_can/m_can.c >> @@ -126,6 +126,12 @@ enum m_can_mram_cfg { >> #define DBTP_DSJW_SHIFT 0 >> #define DBTP_DSJW_MASK (0xf << DBTP_DSJW_SHIFT) >> >> +/* Transmitter Delay Compensation Register (TDCR) */ >> +#define TDCR_TDCO_SHIFT 8 >> +#define TDCR_TDCO_MASK (0x7F << TDCR_TDCO_SHIFT) >> +#define TDCR_TDCF_SHIFT 0 >> +#define TDCR_TDCF_MASK (0x7F << TDCR_TDCO_SHIFT) >> + >> /* Test Register (TEST) */ >> #define TEST_LBCK BIT(4) >> >> @@ -977,6 +983,8 @@ static int m_can_set_bittiming(struct net_device *dev) >> const struct can_bittiming *dbt = &priv->can.data_bittiming; >> u16 brp, sjw, tseg1, tseg2; >> u32 reg_btp; >> + u32 enable_tdc = 0; >> + u32 tdco; >> >> brp = bt->brp - 1; >> sjw = bt->sjw - 1; >> @@ -991,9 +999,23 @@ static int m_can_set_bittiming(struct net_device *dev) >> sjw = dbt->sjw - 1; >> tseg1 = dbt->prop_seg + dbt->phase_seg1 - 1; >> tseg2 = dbt->phase_seg2 - 1; >> + >> + /* TDC is only needed for bitrates beyond 2.5 MBit/s >> + * Specified in the "Bit Time Requirements for CAN FD" document >> + */ >> + if (dbt->bitrate > 2500000) { >> + enable_tdc = DBTP_TDC; >> + /* Equation based on Bosch's M_CAN User Manual's >> + * Transmitter Delay Compensation Section >> + */ >> + tdco = priv->can.clock.freq / (dbt->bitrate * 2); >> + m_can_write(priv, M_CAN_TDCR, tdco << TDCR_TDCO_SHIFT); >> + } >> + >> reg_btp = (brp << DBTP_DBRP_SHIFT) | (sjw << DBTP_DSJW_SHIFT) | >> (tseg1 << DBTP_DTSEG1_SHIFT) | >> - (tseg2 << DBTP_DTSEG2_SHIFT); >> + (tseg2 << DBTP_DTSEG2_SHIFT) | enable_tdc; >> + >> m_can_write(priv, M_CAN_DBTP, reg_btp); >> } >> >>