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b=KvF5YnNVLgMZR0v/DQ4/wXGw+ffESzaU5GFvlRs/k7QAXw1oYVGJKyFRV2Ii3RARh1eX812mf1T1DWo+LdVaU74qyEHpQ7xcHj7+P2UTxBg0vMtqOiRnNs3Lk6OMAzVVZ0kX8kFEddLTfltiKB+5GMzcyBvF97+e/rLn9Jvdo5o= Received: from DM6PR02MB5386.namprd02.prod.outlook.com (2603:10b6:5:75::25) by PH0PR02MB7173.namprd02.prod.outlook.com (2603:10b6:510:d::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5293.13; Thu, 26 May 2022 15:51:33 +0000 Received: from DM6PR02MB5386.namprd02.prod.outlook.com ([fe80::8424:619a:69c2:f7c4]) by DM6PR02MB5386.namprd02.prod.outlook.com ([fe80::8424:619a:69c2:f7c4%5]) with mapi id 15.20.5273.023; Thu, 26 May 2022 15:51:33 +0000 From: Srinivas Neeli To: Vincent Mailhol CC: "wg@grandegger.com" , "mkl@pengutronix.de" , "davem@davemloft.net" , "edumazet@google.com" , Appana Durga Kedareswara Rao , Srinivas Goud , Michal Simek , "kuba@kernel.org" , "pabeni@redhat.com" , "linux-can@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , git Subject: RE: [PATCH] can: xilinx_can: Add Transmitter delay compensation (TDC) feature support Thread-Topic: [PATCH] can: xilinx_can: Add Transmitter delay compensation (TDC) feature support Thread-Index: AQHYZgiBbBEu5TjXQUWU1Nf6kD+jaa0cBDUAgBVfxOA= Date: Thu, 26 May 2022 15:51:33 +0000 Message-ID: References: <20220512135901.1377087-1-srinivas.neeli@xilinx.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-Auto-Response-Suppress: DR, RN, NRN, OOF, AutoReply X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=xilinx.com; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Vincent, > -----Original Message----- > From: Vincent Mailhol > Sent: Friday, May 13, 2022 6:54 AM > To: Srinivas Neeli > Cc: wg@grandegger.com; mkl@pengutronix.de; davem@davemloft.net; > edumazet@google.com; Appana Durga Kedareswara Rao > ; Srinivas Goud ; Michal Simek > ; kuba@kernel.org; pabeni@redhat.com; linux- > can@vger.kernel.org; netdev@vger.kernel.org; linux-arm- > kernel@lists.infradead.org; linux-kernel@vger.kernel.org; git > > Subject: Re: [PATCH] can: xilinx_can: Add Transmitter delay compensation > (TDC) feature support > > On Fri. 13 May 2022 at 07:30, Srinivas Neeli > wrote: > > Added Transmitter delay compensation (TDC) feature support. > > In the case of higher measured loop delay with higher baud rates, > > observed bit stuff errors. > > By enabling the TDC feature in a controller, will compensate for the > > measure loop delay in the receive path. > > TDC feature requires BRP values can be 1 or 2. > > The current CAN framework does not limit the brp so while using TDC, > > have to restrict BRP values. > > Ex: > > ip link set can0 type can tq 12 prop-seg 39 phase-seg1 20 phase-seg2 > > 20 sjw 20 dtq 12 dprop-seg 5 dphase-seg1 6 dphase-seg2 4 dsjw 4 fd on > > loopback on tdco 12 tdc-mode auto > > Did you experience some cases in which you had BRP > 2 and saw > transmission errors due to the absence of delay compensation? Could you > show the calculated values? > Usually, you start to observe but stuff error at high bitrates (e.g. > ~5MBPS), and for such bitrates, time quanta has to be small which then > results in a small BRP. yes, we observed errors with higher baud rates(4 and 5 MBPS). Observation: BRPA 1Mbps Sampling 75% BRPD 5MBPS Sampling 75% On NXP PHY observed a delay of 160 ns. so observing the failure. After enabling the TDC feature to work fine. > > > Signed-off-by: Srinivas Neeli > > --- > > drivers/net/can/xilinx_can.c | 30 +++++++++++++++++++++++++----- > > 1 file changed, 25 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/net/can/xilinx_can.c > > b/drivers/net/can/xilinx_can.c index e2b15d29d15e..7af518fbed02 100644 > > --- a/drivers/net/can/xilinx_can.c > > +++ b/drivers/net/can/xilinx_can.c > > @@ -1,7 +1,7 @@ > > // SPDX-License-Identifier: GPL-2.0-or-later > > /* Xilinx CAN device driver > > * > > - * Copyright (C) 2012 - 2014 Xilinx, Inc. > > + * Copyright (C) 2012 - 2022 Xilinx, Inc. > > * Copyright (C) 2009 PetaLogix. All rights reserved. > > * Copyright (C) 2017 - 2018 Sandvik Mining and Construction Oy > > * > > @@ -133,6 +133,8 @@ enum xcan_reg { > > #define XCAN_DLCR_BRS_MASK 0x04000000 /* BRS Mask in DLC */ > > > > /* CAN register bit shift - XCAN___SHIFT */ > > +#define XCAN_BRPR_TDCO_SHIFT_CANFD 8 /* Transmitter Delay > Compensation Offset */ > > Having CANFD in the name is redundant (TDC implies CANFD). > #define XCAN_BRPR_TDCO_SHIFT 8 update in V2. > > > +#define XCAN_BRPR_TDCE_SHIFT_CANFD 16 /* Transmitter Delay > Compensation (TDC) Enable */ > > Why not: > #define XCAN_BRPR_TDC_ENABLE BIT(16) update in V2. > > > #define XCAN_BTR_SJW_SHIFT 7 /* Synchronous jump width */ > > #define XCAN_BTR_TS2_SHIFT 4 /* Time segment 2 */ > > #define XCAN_BTR_SJW_SHIFT_CANFD 16 /* Synchronous jump width > */ > > @@ -259,7 +261,7 @@ static const struct can_bittiming_const > xcan_bittiming_const_canfd2 = { > > .tseg2_min = 1, > > .tseg2_max = 128, > > .sjw_max = 128, > > - .brp_min = 2, > > + .brp_min = 1, > > Was there any reason to have brp_min = 2 in the first place? > I think this change should be a different patch. If the brp_min = 2 is just a > typo, you might also want to backport it to stable branches. On early silicon engineering samples we observed bit shrinking issue when we use brp =1 , hence we updated brp_min =2. As in production silicon this issue is fixed we are planning to revert the patch. > > > .brp_max = 256, > > .brp_inc = 1, > > }; > > @@ -272,11 +274,21 @@ static struct can_bittiming_const > xcan_data_bittiming_const_canfd2 = { > > .tseg2_min = 1, > > .tseg2_max = 16, > > .sjw_max = 16, > > - .brp_min = 2, > > + .brp_min = 1, > > .brp_max = 256, > > .brp_inc = 1, > > }; > > > > +/* Transmission Delay Compensation constants for CANFD2.0 and Versal > > +*/ static const struct can_tdc_const xcan_tdc_const = { > > + .tdcv_min = 0, > > + .tdcv_max = 0, /* Manual mode not supported. */ > > Right, had a look at the datasheet and xilinx indeed does not support setting > TDCV. > However, xilinx still has a TDCV register to report the measured transmission > delay. > > Socket CAN's TDC framework provides can_priv::do_get_auto_tdcv() to > report the measured value through the netlink interface: > https://elixir.bootlin.com/linux/v5.17/source/include/linux/can/dev.h#L87 > > Can you implement this call back function? Will implement in V2. > > > + .tdco_min = 0, > > + .tdco_max = 64, > > + .tdcf_min = 0, /* Filter window not supported */ > > + .tdcf_max = 0, > > +}; > > + > > /** > > * xcan_write_reg_le - Write a value to the device register little endian > > * @priv: Driver private data structure > > @@ -425,6 +437,11 @@ static int xcan_set_bittiming(struct net_device > *ndev) > > priv->devtype.cantype == XAXI_CANFD_2_0) { > > /* Setting Baud Rate prescalar value in F_BRPR Register */ > > btr0 = dbt->brp - 1; > > + if (can_tdc_is_enabled(&priv->can)) { > > + btr0 = btr0 | > > + (priv->can.tdc.tdco) << XCAN_BRPR_TDCO_SHIFT_CANFD | > > + 1 << XCAN_BRPR_TDCE_SHIFT_CANFD; > > I don't think the parenthesis around (priv->can.tdc.tdco) are needed. Yes, will update. > > btr0 = btr0 | > priv->can.tdc.tdco << XCAN_BRPR_TDCO_SHIFT | > XCAN_BRPR_TDC_ENABLE > > (c.f. above for macro names) > > > + } > > > > /* Setting Time Segment 1 in BTR Register */ > > btr1 = dbt->prop_seg + dbt->phase_seg1 - 1; @@ > > -1747,13 +1764,16 @@ static int xcan_probe(struct platform_device *pdev) > > priv->can.data_bittiming_const = > > &xcan_data_bittiming_const_canfd; > > > > - if (devtype->cantype == XAXI_CANFD_2_0) > > + if (devtype->cantype == XAXI_CANFD_2_0) { > > priv->can.data_bittiming_const = > > &xcan_data_bittiming_const_canfd2; > > + priv->can.tdc_const = &xcan_tdc_const; > > + } > > > > if (devtype->cantype == XAXI_CANFD || > > devtype->cantype == XAXI_CANFD_2_0) > > - priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD; > > + priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD | > > + CAN_CTRLMODE_TDC_AUTO; > > > > priv->reg_base = addr; > > priv->tx_max = tx_max; > > -- > > 2.25.1 > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel