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Subject: Re: [PATCH v9 1/4] can: m_can: Create a m_can platform framework
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
References: <20190313162629.11937-1-dmurphy@ti.com>
 <87f14a09-244e-c698-1372-f8b49e60faee@grandegger.com>
 <a578dd22-a581-8421-fac4-605fa8f63d1a@ti.com>
From:   Wolfgang Grandegger <wg@grandegger.com>
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Message-ID: <470e0028-7e4c-b1ba-7c50-7464f4904801@grandegger.com>
Date:   Thu, 14 Mar 2019 15:38:23 +0100
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Hello,

Am 14.03.19 um 15:04 schrieb Dan Murphy:
> Hello
> 
> On 3/14/19 2:26 AM, Wolfgang Grandegger wrote:
>> Hello Dan,
>>
>> we are close...
>>
>> Am 13.03.19 um 17:26 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>
>>> ---
>>>
>>> v9 - Added back the CSR clearing as this is needed for TCAN device, fixed clean
>>> function to clean index for version > 30, removed extra skb free and fixed work
>>> handler to handle FIFO full for perpheral devices - https://lore.kernel.org/patchwork/patch/1050120/
>>>
>>> v8 - Added a clean function for the tx_skb, cleaned up skb on BUS_OFF and on xmit
>>> BUSY - https://lore.kernel.org/patchwork/patch/1047980/
>>> 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          | 733 +++++++++++++------------
>>>  drivers/net/can/m_can/m_can.h          | 110 ++++
>>>  drivers/net/can/m_can/m_can_platform.c | 202 +++++++
>>>  5 files changed, 714 insertions(+), 345 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..56336aefc567 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;
>>> +		}
>>> +
>>> +		if (priv->can.state == CAN_STATE_BUS_OFF) {
>>> +			m_can_clean(dev);
>>> +		} else {
>>> +			priv->tx_skb = skb;
>>> +			queue_work(priv->tx_wq, &priv->tx_work);
>>
>> You removed "netif_stop_queue(cdev->net)" here. Does that work with just
>> *one* "tx_skb"? I think you need an array then!? I'm afraid, this will
>> require quite some changes and you should also measure the benefit of
>> queuing outgoing messages first. For the time being, it would be fine
>> for me to stop the queue here and add an appropriate comment.
>>
> 
> Yes I removed this in favor of allowing the work handler to stop the queue.
> 
> If the version is < 30 then the queue is stopped immediately.  If the version > 30 then the queue is
> only stopped if FIFO is full.

Yes, and the next call to m_can_start_xmit() will probably return with
NETDEV_TX_BUSY. You should at least add a "netif_stop_queue(cdev->net)"
before returning NETDEV_TX_BUSY, otherwice the upper layer will retry
immediately resulting in high CPU load. Anyway, the purpose of this
return code is to signal errors/bugs in the start/stop flow control:

https://elixir.bootlin.com/linux/latest/source/Documentation/networking/netdevices.txt#L81

> 
> I did see the message "tcan4x5x spi1.0 can0: hard_xmit called while tx busy" 
> more with no gap and no polling in the cangen request.

You usually should never see that message.

> 
>> BTW, how big is the FIFO size on your system:
>>
> 
> This value is set to 1.
> 
>>   tx_fifo_size = mram_config_vals[7];

Then I'm surprised that you see "hard_xmit called while tx busy" at all.
Are you sure that "cdev->version" is 32 on the tcan4x5?

Wolfgang