Date:   Wed, 13 Jan 2021 21:15:04 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     linux-can <linux-can@...r.kernel.org>,
        Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jimmy Assarsson <extja@...ser.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "open list : NETWORKING DRIVERS" <netdev@...r.kernel.org>
Subject: Re: [PATCH v10 1/1] can: usb: etas_es58X: add support for ETAS ES58X
 CAN USB interfaces

Hi Marc,

Thanks for the comments!

On Wed. 13 Jan 2021 à 18:33, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>
> On 1/12/21 2:05 PM, Vincent Mailhol wrote:
> > This driver supports the ES581.4, ES582.1 and ES584.1 interfaces from
> > ETAS GmbH (https://www.etas.com/en/products/es58x.php).
> >
> > Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>
> > Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>
> > Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
>
> [...]
>
> > diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c b/drivers/net/can/usb/etas_es58x/es58x_core.c
> > new file mode 100644
> > index 000000000000..30692d78d8e6
> > --- /dev/null
> > +++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
> > @@ -0,0 +1,2589 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/* Driver for ETAS GmbH ES58X USB CAN(-FD) Bus Interfaces.
> > + *
> > + * File es58x_core.c: Core logic to manage the network devices and the
> > + * USB interface.
> > + *
> > + * Copyright (C) 2019 Robert Bosch Engineering and Business
> > + * Solutions. All rights reserved.
> > + * Copyright (C) 2020 ETAS K.K.. All rights reserved.
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/moduleparam.h>
> > +#include <linux/usb.h>
> > +#include <linux/crc16.h>
> > +#include <linux/spinlock.h>
> > +#include <asm/unaligned.h>
> > +
> > +#include "es58x_core.h"
> > +
> > +#define DRV_VERSION "1.00"
> > +MODULE_AUTHOR("Mailhol Vincent <mailhol.vincent@...adoo.fr>");
> > +MODULE_AUTHOR("Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>");
> > +MODULE_DESCRIPTION("Socket CAN driver for ETAS ES58X USB adapters");
> > +MODULE_VERSION(DRV_VERSION);
> > +MODULE_LICENSE("GPL v2");
> > +
> > +/* Vendor and product id */
> > +#define ES58X_MODULE_NAME "etas_es58x"
> > +#define ES58X_VENDOR_ID 0x108C
> > +#define ES581_4_PRODUCT_ID 0x0159
> > +#define ES582_1_PRODUCT_ID 0x0168
> > +#define ES584_1_PRODUCT_ID 0x0169
> > +
> > +/* Table of devices which work with this driver */
> > +static const struct usb_device_id es58x_id_table[] = {
> > +     {USB_DEVICE(ES58X_VENDOR_ID, ES581_4_PRODUCT_ID)},
> > +     {USB_DEVICE(ES58X_VENDOR_ID, ES582_1_PRODUCT_ID)},
> > +     {USB_DEVICE(ES58X_VENDOR_ID, ES584_1_PRODUCT_ID)},
> > +     {}                      /* Terminating entry */
> > +};
> > +
> > +MODULE_DEVICE_TABLE(usb, es58x_id_table);
> > +
> > +#define es58x_print_hex_dump(buf, len)                                       \
> > +     print_hex_dump(KERN_DEBUG,                                      \
> > +                    ES58X_MODULE_NAME " " __stringify(buf) ": ",     \
> > +                    DUMP_PREFIX_NONE, 16, 1, buf, len, false)
> > +
> > +#define es58x_print_hex_dump_debug(buf, len)                          \
> > +     print_hex_dump_debug(ES58X_MODULE_NAME " " __stringify(buf) ": ",\
> > +                          DUMP_PREFIX_NONE, 16, 1, buf, len, false)
> > +
> > +/* The last two bytes of an ES58X command is a CRC16. The first two
> > + * bytes (the start of frame) are skipped and the CRC calculation
> > + * starts on the third byte.
> > + */
> > +#define ES58X_CRC_CALC_OFFSET        2
> > +
> > +/**
> > + * es58x_calculate_crc() - Compute the crc16 of a given URB.
> > + * @urb_cmd: The URB command for which we want to calculate the CRC.
> > + * @urb_len: Length of @urb_cmd. Must be at least bigger than 4
> > + *   (ES58X_CRC_CALC_OFFSET + sizeof(crc))
> > + *
> > + * Return: crc16 value.
> > + */
> > +static u16 es58x_calculate_crc(const union es58x_urb_cmd *urb_cmd, u16 urb_len)
> > +{
> > +     u16 crc;
> > +     ssize_t len = urb_len - ES58X_CRC_CALC_OFFSET - sizeof(crc);
> > +
> > +     WARN_ON(len < 0);
>
> Is it possible to ensure earlier, that the urbs are of correct length?

Easy answer: it is ensured. On the Tx branch, I create the urbs so I
know for sure that the length is correct. On the Rx branch, I have a
dedicated function: es58x_check_rx_urb() for this purpose.  I
will remove that WARN_ON() and the one in es58x_get_crc().

I will also check the other WARN_ON() in my code to see if they
can be removed (none on my test throughout the last ten months or
so could trigger any of these WARN_ON() so should be fine to
remove but I will double check).

> > +     crc = crc16(0, &urb_cmd->raw_cmd[ES58X_CRC_CALC_OFFSET], len);
> > +     return crc;
> > +}
>
> [...]
>
> > +/**
> > + * struct es58x_priv - All information specific to a CAN channel.
> > + * @can: struct can_priv must be the first member (Socket CAN relies
> > + *   on the fact that function netdev_priv() returns a pointer to
> > + *   a struct can_priv).
> > + * @es58x_dev: pointer to the corresponding ES58X device.
> > + * @tx_urb: Used as a buffer to concatenate the TX messages and to do
> > + *   a bulk send. Please refer to es58x_start_xmit() for more
> > + *   details.
> > + * @echo_skb_spinlock: Spinlock to protect the access to the echo skb
> > + *   FIFO.
> > + * @current_packet_idx: Keeps track of the packet indexes.
> > + * @echo_skb_tail_idx: beginning of the echo skb FIFO, i.e. index of
> > + *   the first element.
> > + * @echo_skb_head_idx: end of the echo skb FIFO plus one, i.e. first
> > + *   free index.
> > + * @num_echo_skb: actual number of elements in the FIFO. Thus, the end
> > + *   of the FIFO is echo_skb_head = (echo_skb_tail_idx +
> > + *   num_echo_skb) % can.echo_skb_max.
> > + * @tx_total_frame_len: sum, in bytes, of the length of each of the
> > + *   CAN messages contained in @tx_urb. To be used as an input of
> > + *   netdev_sent_queue() for BQL.
> > + * @tx_can_msg_cnt: Number of messages in @tx_urb.
> > + * @tx_can_msg_is_fd: false: all messages in @tx_urb are Classical
> > + *   CAN, true: all messages in @tx_urb are CAN FD. Rationale:
> > + *   ES58X FD devices do not allow to mix Classical CAN and FD CAN
> > + *   frames in one single bulk transmission.
> > + * @err_passive_before_rtx_success: The ES58X device might enter in a
> > + *   state in which it keeps alternating between error passive
> > + *   and active state. This counter keeps track of the number of
> > + *   error passive and if it gets bigger than
> > + *   ES58X_CONSECUTIVE_ERR_PASSIVE_MAX, es58x_rx_err_msg() will
> > + *   force the status to bus-off.
> > + * @channel_idx: Channel index, starts at zero.
> > + */
> > +struct es58x_priv {
> > +     struct can_priv can;
> > +     struct es58x_device *es58x_dev;
> > +     struct urb *tx_urb;
> > +
> > +     spinlock_t echo_skb_spinlock;   /* Comments: c.f. supra */
> > +     u32 current_packet_idx;
> > +     u16 echo_skb_tail_idx;
> > +     u16 echo_skb_head_idx;
> > +     u16 num_echo_skb;
>
> Can you explain me how the tx-path works, especially why you need the
> current_packet_idx.
>
> In the mcp251xfd driver, the number of TX buffers is a power of two, that makes
> things easier. tx_heads % len points to the next buffer to be filled, tx_tail %
> len points to the next buffer to be completed. tx_head - tx_tail is the fill
> level of the FIFO. This works without spinlocks.

For what I understand of your explanations here are the equivalences
between the etas_es58x and the mcp251xfd drivers:

 +--------------------+-------------------+
 | etas_es58x         | mcp251xfd         |
 +--------------------+-------------------+
 | current_packet_idx | tx_head           |
 | echo_skb_tail_idx  | tx_tail % len     |
 | echo_skb_head_idx  | tx_head % len     |
 | num_echo_skb       | tx_head - tx_tail |
 +--------------------+-------------------+

Especially, the current_packet_idx is sent to the device and returned
to the driver upon completion.

I wish the TX buffers were a power of two which is unfortunately not
the case. The theoretical TX buffer sizes are 330 and 500 for the two
devices so I wrote the code to work with those values. The exact size
of the TX buffer is actually even more of a mystery because during
testing both devices were unstable when using the theoretical values
and I had to lower these. There is a comment at the bottom of
es581_4.c and es58x_fd.c to reflect those issues. Because I do not
have access to the source code of the firmware, I could not identify
the root cause.

My understanding is that having a queue size being a power of two is
required in order not to use spinlocks (else, modulo operations would
break when the index wraparound back to zero). I tried to minimize the
number of spinlock: only one per bulk send or bulk receive.


Yours sincerely,
Vincent


> > +
> > +     u16 tx_total_frame_len;
> > +     u8 tx_can_msg_cnt;
> > +     bool tx_can_msg_is_fd;
> > +
> > +     u8 err_passive_before_rtx_success;
> > +
> > +     u8 channel_idx;
> > +};
>
> Marc
>
> --
> Pengutronix e.K.                 | Marc Kleine-Budde           |
> Embedded Linux                   | https://www.pengutronix.de  |
> Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
> Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |
>

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