netdev - Re: [RESEND PATCH v5 1/2] can: rcar_canfd: Add Renesas R-Car CAN FD driver

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Date:	Fri, 3 Jun 2016 19:03:41 +0200
From:	Ulrich Hecht <ulrich.hecht@...il.com>
To:	Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>
Cc:	"mkl@...gutronix.de" <mkl@...gutronix.de>,
	"wg@...ndegger.com" <wg@...ndegger.com>,
	"socketcan@...tkopp.net" <socketcan@...tkopp.net>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Chris Paterson <Chris.Paterson2@...esas.com>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	"linux-renesas-soc@...r.kernel.org" 
	<linux-renesas-soc@...r.kernel.org>
Subject: Re: [RESEND PATCH v5 1/2] can: rcar_canfd: Add Renesas R-Car CAN FD driver

On Fri, Jun 3, 2016 at 8:42 AM, Ramesh Shanmugasundaram
<ramesh.shanmugasundaram@...renesas.com> wrote:
> Hi Uli,
>
> Thanks for the review
>
>> Thank you for your patch.
>>
>> On Thu, Jun 2, 2016 at 11:45 AM, Ramesh Shanmugasundaram
>> <ramesh.shanmugasundaram@...renesas.com> wrote:
>> [...]
>> > diff --git a/drivers/net/can/rcar/rcar_canfd.c
>> > b/drivers/net/can/rcar/rcar_canfd.c
>> > new file mode 100644
>> > index 0000000..e198732
>> > --- /dev/null
>> > +++ b/drivers/net/can/rcar/rcar_canfd.c
>> > @@ -0,0 +1,1624 @@
>> > +/* Renesas R-Car CAN FD device driver
>> > + *
>> > + * Copyright (C) 2015 Renesas Electronics Corp.
>> > + *
>> > + * This program is free software; you can redistribute  it and/or
>> > +modify it
>> > + * under  the terms of  the GNU General  Public License as published
>> > +by the
>> > + * Free Software Foundation;  either version 2 of the  License, or
>> > +(at your
>> > + * option) any later version.
>> > + */
>> > +
>> > +/* The R-Car CAN FD controller can operate in either one of the below
>> > +two modes
>> > + *  - CAN FD only mode
>> > + *  - Classical CAN (CAN 2.0) only mode
>> > + *
>> > + * This driver puts the controller in CAN FD only mode by default. In
>> > +this
>> > + * mode, the controller acts as a CAN FD node that can also
>> > +interoperate with
>> > + * CAN 2.0 nodes.
>> > + *
>> > + * As of now, this driver does not support the Classical CAN (CAN
>> > +2.0) mode,
>> > + * which is handled by a different register map compared to CAN FD only
>> mode.
>> > + */
>> > +
>> > +#include <linux/module.h>
>> > +#include <linux/moduleparam.h>
>> > +#include <linux/kernel.h>
>> > +#include <linux/types.h>
>> > +#include <linux/interrupt.h>
>> > +#include <linux/errno.h>
>> > +#include <linux/netdevice.h>
>> > +#include <linux/platform_device.h>
>> > +#include <linux/can/led.h>
>> > +#include <linux/can/dev.h>
>> > +#include <linux/clk.h>
>> > +#include <linux/of.h>
>> > +#include <linux/of_device.h>
>> > +#include <linux/bitmap.h>
>> > +#include <linux/bitops.h>
>> > +#include <linux/iopoll.h>
>> > +
>> > +#define RCANFD_DRV_NAME                        "rcar_canfd"
>> > +
>> > +#define RCANFD_FIFO_DEPTH              8       /* Tx FIFO depth */
>> > +#define RCANFD_NAPI_WEIGHT             8       /* Rx poll quota */
>> > +
>> > +#define RCANFD_NUM_CHANNELS            2       /* Two channels max */
>> > +#define RCANFD_CHANNELS_MASK           BIT((RCANFD_NUM_CHANNELS) - 1)
>> > +
>> > +/* Rx FIFO is a global resource of the controller. There are 8 such
>> > +FIFOs
>> > + * available. Each channel gets a dedicated Rx FIFO (i.e.) the
>> > +channel
>> > + * number is added to RFFIFO index.
>> > + */
>> > +#define RCANFD_RFFIFO_IDX              0
>> > +
>> > +/* Tx/Rx or Common FIFO is a per channel resource. Each channel has 3
>> > +Common
>> > + * FIFOs dedicated to them. Use the first (index 0) FIFO out of the 3
>> for Tx.
>> > + */
>> > +#define RCANFD_CFFIFO_IDX              0
>> > +
>> > +/* Global register bits */
>> > +#define RCANFD_GINTF_CANFD             BIT(0)
>> > +
>> > +#define RCANFD_GCFG_TPRI               BIT(0)
>> > +#define RCANFD_GCFG_DCE                        BIT(1)
>> > +#define RCANFD_GCFG_DCS                        BIT(4)
>> > +#define RCANFD_GCFG_CMPOC              BIT(5)
>>
>> What reference are the register layouts based on? This bit, for instance,
>> is marked reserved in R-Car-Gen3-rev0.51e.pdf, and many are named
>> differently.
>
> It is based on rev0.51e Gen3 h/w manual. This controller has two register maps within itself for classical CAN only mode or CAN FD only mode. Section 52A.7.3.1 defines GCFG classical CAN only mode where bit 5 is reserved and Section 52A.9.3.1 defines GCFG CAN FD mode where bit 5 is defined as CMPOC.

Thanks; I missed that every register is described twice.

Nevertheless, names often vary more or less subtly between your patch
and the specs, making it very hard to review. Some have letters added,
some have letters removed, and some are just plain confusing. For
instance, RCANFD_DCFG_* apparently does not describe, as one might
think, RSCFDnCFDCmDCFG, but RSCFDnCFDCmFDCFG. These names are, of
course, completely ridiculous, but inventing a new set makes things
even worse, IMO.

At least for the bits, I'd stick with the names given in the
datasheet. They usually make a modicum of sense, and it makes it way
easier to search for them. It would also help if the bits were sorted
consistently.

CU
Uli