linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Wolfgang Grandegger <wg@grandegger.com>
To: Dan Murphy <dmurphy@ti.com>, mkl@pengutronix.de, davem@davemloft.net
Cc: linux-can@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 1/4] can: m_can: Create a m_can platform framework
Date: Fri, 8 Mar 2019 19:06:00 +0100	[thread overview]
Message-ID: <e8782172-5156-6704-8ddb-b7d4d670e3c9@grandegger.com> (raw)
In-Reply-To: <a2538a05-a03f-06f8-99e3-c7c72287613c@ti.com>



Am 08.03.19 um 18:52 schrieb Dan Murphy:
> On 3/8/19 11:40 AM, Wolfgang Grandegger wrote:
>> Hello Dan,
>>
>> Am 08.03.19 um 18:25 schrieb Dan Murphy:
>>> On 3/8/19 11:08 AM, Wolfgang Grandegger wrote:
>>>> Hello,
>>>>
>>>> Am 08.03.19 um 16:48 schrieb Dan Murphy:
>>>>> Wolfgang
>>>>>
>>>>> On 3/8/19 8:41 AM, Wolfgang Grandegger wrote:
>>>>>> Hello Dan,
>>>>>>
>>>>>> thinking more about it...
>>>>>>
>>>>>> Am 08.03.19 um 14:29 schrieb Wolfgang Grandegger:
>>>>>>> Hello Dan,
>>>>>>>
>>>>>>> Am 08.03.19 um 13:44 schrieb Dan Murphy:
>>>>>>>> Wolfgang
>>>>>>>>
>>>>>>>> On 3/8/19 4:10 AM, Wolfgang Grandegger wrote:
>>>>>>>>> Hallo Dan,
>>>>>>>>>
>>>>>>>>> Am 05.03.19 um 16:52 schrieb Dan Murphy:
>>>>>>>>>> Create a m_can platform framework that peripherial
>>>>>>>>>> devices can register to and use common code and register sets.
>>>>>>>>>> The peripherial devices may provide read/write and configuration
>>>>>>>>>> support of the IP.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Dan Murphy <dmurphy@ti.com>
>>>>>>>>>> ---
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> v7 - Fixed remaining new checkpatch issues, removed CSR setting, fixed tx hard
>>>>>>>>>> start function to return tx_busy, and renamed device callbacks - https://lore.kernel.org/patchwork/patch/1047220/
>>>>>>>>>>
>>>>>>>>>> v6 - Squashed platform patch to this patch for bissectablity, fixed coding style
>>>>>>>>>> issues, updated Kconfig help, placed mcan reg offsets back into c file, renamed
>>>>>>>>>> priv->skb to priv->tx_skb and cleared perp interrupts at ISR start -
>>>>>>>>>> Patch 1 comments - https://lore.kernel.org/patchwork/patch/1042446/
>>>>>>>>>> Patch 2 comments - https://lore.kernel.org/patchwork/patch/1042442/
>>>>>>>>>>
>>>>>>>>>>  drivers/net/can/m_can/Kconfig          |  13 +-
>>>>>>>>>>  drivers/net/can/m_can/Makefile         |   1 +
>>>>>>>>>>  drivers/net/can/m_can/m_can.c          | 700 +++++++++++++------------
>>>>>>>>>>  drivers/net/can/m_can/m_can.h          | 110 ++++
>>>>>>>>>>  drivers/net/can/m_can/m_can_platform.c | 202 +++++++
>>>>>>>>>>  5 files changed, 682 insertions(+), 344 deletions(-)
>>>>>>>>>>  create mode 100644 drivers/net/can/m_can/m_can.h
>>>>>>>>>>  create mode 100644 drivers/net/can/m_can/m_can_platform.c
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/net/can/m_can/Kconfig b/drivers/net/can/m_can/Kconfig
>>>>>>>>>> index 04f20dd39007..f7119fd72df4 100644
>>>>>>>>>> --- a/drivers/net/can/m_can/Kconfig
>>>>>>>>>> +++ b/drivers/net/can/m_can/Kconfig
>>>>>>>>>> @@ -1,5 +1,14 @@
>>>>>>>>>>  config CAN_M_CAN
>>>>>>>>>> +	tristate "Bosch M_CAN support"
>>>>>>>>>> +	---help---
>>>>>>>>>> +	  Say Y here if you want support for Bosch M_CAN controller framework.
>>>>>>>>>> +	  This is common support for devices that embed the Bosch M_CAN IP.
>>>>>>>>>> +
>>>>>>>>>> +config CAN_M_CAN_PLATFORM
>>>>>>>>>> +	tristate "Bosch M_CAN support for io-mapped devices"
>>>>>>>>>>  	depends on HAS_IOMEM
>>>>>>>>>> -	tristate "Bosch M_CAN devices"
>>>>>>>>>> +	depends on CAN_M_CAN
>>>>>>>>>>  	---help---
>>>>>>>>>> -	  Say Y here if you want to support for Bosch M_CAN controller.
>>>>>>>>>> +	  Say Y here if you want support for IO Mapped Bosch M_CAN controller.
>>>>>>>>>> +	  This support is for devices that have the Bosch M_CAN controller
>>>>>>>>>> +	  IP embedded into the device and the IP is IO Mapped to the processor.
>>>>>>>>>> diff --git a/drivers/net/can/m_can/Makefile b/drivers/net/can/m_can/Makefile
>>>>>>>>>> index 8bbd7f24f5be..057bbcdb3c74 100644
>>>>>>>>>> --- a/drivers/net/can/m_can/Makefile
>>>>>>>>>> +++ b/drivers/net/can/m_can/Makefile
>>>>>>>>>> @@ -3,3 +3,4 @@
>>>>>>>>>>  #
>>>>>>>>>>  
>>>>>>>>>>  obj-$(CONFIG_CAN_M_CAN) += m_can.o
>>>>>>>>>> +obj-$(CONFIG_CAN_M_CAN_PLATFORM) += m_can_platform.o
>>>>>>>>>> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
>>>>>>>>>> index 9b449400376b..a60278d94126 100644
>>>>>>>>>> --- a/drivers/net/can/m_can/m_can.c
>>>>>>>>>> +++ b/drivers/net/can/m_can/m_can.c
>>>>>>>>>
>>>>>>>>> ... snip...
>>>>>>>>>
>>>>>>>>>> +static netdev_tx_t m_can_start_xmit(struct sk_buff *skb,
>>>>>>>>>> +				    struct net_device *dev)
>>>>>>>>>> +{
>>>>>>>>>> +	struct m_can_priv *priv = netdev_priv(dev);
>>>>>>>>>> +
>>>>>>>>>> +	if (can_dropped_invalid_skb(dev, skb))
>>>>>>>>>> +		return NETDEV_TX_OK;
>>>>>>>>>> +
>>>>>>>>>> +	if (priv->is_peripherial) {
>>>>>>>>>> +		if (priv->tx_skb) {
>>>>>>>>>> +			netdev_err(dev, "hard_xmit called while tx busy\n");
>>>>>>>>>> +			return NETDEV_TX_BUSY;
>>>>>>>>>> +		}
>>>>>>>>>
>>>>>>>>> The problem with that approach is, that the upper layer will try to
>>>>>>>>> resubmit the current "skb" but not the previous "tx_skb". And the
>>>>>>>>> previous "tx_skb" has not been freed yet. I would just drop and free the
>>>>>>>>> skb and return NETDEV_TX_OK in m_can_tx_handler() for peripheral devices
>>>>>>>>> (like can_dropped_invalid_skb() does).
>>>>>>>>>
>>>>>>>>
>>>>>>>> OK.
>>>>>>>>
>>>>>>>> So would this also be a bug in the hi3110 and mcp251x drivers (line 521) as well because besides checking tx_length
>>>>>>>> this is how these drivers are written.
>>>>>>>
>>>>>>> This is different. When entering the "start_xmit" routine, the previous
>>>>>>> TX is still in progress. It will (hopefully) complete soon. Therefore
>>>>>>> returning NETDEV_TX_BUSY is OK. The "start_xmit" routine will be
>>>>>>> recalled soon with the same "skb". That scenario should/could also not
>>>>>>> happen.
>>>>>>
>>>>>> In principle, this also applies to the m_can peripheral devices. If
>>>>>> tx_skb is not NULL, the TX is still in progress and returning
>>>>>> NETDEV_TX_BUSY is just fine.
>>>>>>
>>>>>>>
>>>>>>> In contrast, in "m_can_tx_handler()", the skb could not be handled
>>>>>>> because the FIFO is full. The "start_xmit" routine for peripheral
>>>>>>> devices for that skb already returned NETDEV_TX_OK. Therefore the only
>>>>>>> meaningful action is to drop the skb. Also this error should not happen
>>>>>>> and if, something is going really wrong. Therefore I think, a
>>>>>>> WARN_ONCE() would be even more appropriate. But that should be a
>>>>>>> separate patch.
>>>>>>
>>>>>> But that's a different issue/error. The tx_skb cannot be processed in
>>>>>> "m_can_tx_handler()". Either we drop it or we re-queue it (retry later).
>>>>>>
>>>>>
>>>>> OK I am a bit confused on this.  Are you saying this is not an issue?
>>>>> Or are you saying I need to check for tx_len like the other code?
>>>>
>>>> If you check for tx_skb in the "start_xmit" routine like the hi3110 and
>>>> mcp251x, it will work the same way. But only, if the "tx_handler()" has
>>>> fully processed the message. It simple means, the TX is still in
>>>> progress and will complete soon. But in "m_can_tx_handler()" we return
>>>> without handling the message! It will never be sent and freed. Or will
>>>> the "m_can_tx_handler()" retry?
>>>>
>>>
>>> I am not seeing where we are not handling the message in the m_can_tx_handler()
>>
>> static void m_can_tx_handler(struct m_can_classdev *priv)
>> {
>> 		...
>> 		/* Check if FIFO full */
>> 		if (m_can_tx_fifo_full(priv)) {
>> 			/* This shouldn't happen */
>> 			netif_stop_queue(dev);
>> 			netdev_warn(dev,
>> 				    "TX queue active although FIFO is full.");
>> 			return;
>> 		}
>>
>> We simply return here. When is the message (tx_skb) processed (sent or freed)?
>> What happens with tx_skb?
>>
> 
> Are you sure you are looking at the right code?
> 
> For patch version v7 I have the following
> 
> 		/* Check if FIFO full */
> 		if (m_can_tx_fifo_full(cdev)) {
> 			/* This shouldn't happen */
> 			netif_stop_queue(dev);
> 			netdev_warn(dev,
> 				    "TX queue active although FIFO is full.");
> 			return NETDEV_TX_BUSY;
> 		}
> 
> Which is no change from the original source code.

I know,  but for the peripheral devices you have:

  static void m_can_tx_work_queue(struct work_struct *ws)
  {
	struct m_can_priv *priv = container_of(ws, struct m_can_priv,
						tx_work);
	netdev_tx_t ret;

	ret = m_can_tx_handler(priv);
	if (ret == NETDEV_TX_OK)
		priv->tx_skb = NULL;
  }

What will happen with tx_skb if NETDEV_TX_BUSY? It has not been
dropped/freed yet?

Wolfgang.

  reply	other threads:[~2019-03-08 18:06 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-05 15:52 Dan Murphy
2019-03-05 15:52 ` [PATCH v7 2/4] can: m_can: Rename m_can_priv to m_can_classdev Dan Murphy
2019-03-08 10:25   ` Wolfgang Grandegger
2019-03-08 12:33     ` Dan Murphy
2019-03-05 15:52 ` [PATCH v7 3/4] dt-bindings: can: tcan4x5x: Add DT bindings for TCAN4x5X driver Dan Murphy
2019-03-05 15:52 ` [PATCH v7 4/4] can: tcan4x5x: Add tcan4x5x driver to the kernel Dan Murphy
2019-03-08 10:10 ` [PATCH v7 1/4] can: m_can: Create a m_can platform framework Wolfgang Grandegger
2019-03-08 12:44   ` Dan Murphy
2019-03-08 13:29     ` Wolfgang Grandegger
2019-03-08 14:41       ` Wolfgang Grandegger
2019-03-08 15:48         ` Dan Murphy
2019-03-08 17:08           ` Wolfgang Grandegger
2019-03-08 17:25             ` Dan Murphy
2019-03-08 17:40               ` Wolfgang Grandegger
2019-03-08 17:52                 ` Dan Murphy
2019-03-08 18:06                   ` Wolfgang Grandegger [this message]
2019-03-08 20:36                     ` Dan Murphy
2019-03-11 11:19                       ` Wolfgang Grandegger

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=e8782172-5156-6704-8ddb-b7d4d670e3c9@grandegger.com \
    --to=wg@grandegger.com \
    --cc=davem@davemloft.net \
    --cc=dmurphy@ti.com \
    --cc=linux-can@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mkl@pengutronix.de \
    --cc=netdev@vger.kernel.org \
    --subject='Re: [PATCH v7 1/4] can: m_can: Create a m_can platform framework' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).