Re: Writing socketCAN module for my own hardware

[Marc Kleine-Budde <mkl@pengutronix.de>]

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Hello Florian,

please don't top-post.

On 10/09/2014 05:06 PM, Florian Feldbauer wrote:
> I now checked everything with a mixed signal scope and
> one thing came to my eye:
> 
> After loading the module, I get the error:
> [   16.806860] sja1000_raspi sja1000_raspi.0: registering sja1000_raspi
> device (reg_base=0xf2200000, irq=174)
> [   16.836560] sja1000_raspi sja1000_raspi.0 (unregistered net_device):
> setting SJA1000 into reset mode failed!
> [   16.871684] sja1000_raspi sja1000_raspi.0: sja1000_raspi device
> registered (reg_base=0xf2200000, irq=174)
> 
> Although I can see at the scope, that reading register 0 of the SJA1000
> returns the value 1 as it should be.
> Also, it seems that there is some kind of endless loop reading this
> register.

No, just a loop of up to 100 :)

> static void set_reset_mode(struct net_device *dev)                               
> {                                                                                
>         struct sja1000_priv *priv = netdev_priv(dev);                            
>         unsigned char status = priv->read_reg(priv, SJA1000_MOD);                
>         int i;                                                                   
>                                                                                  
>         /* disable interrupts */                                                 
>         priv->write_reg(priv, SJA1000_IER, IRQ_OFF);                             
>                                                                                  
>         for (i = 0; i < 100; i++) {                                              
>                 /* check reset bit */                                            
>                 if (status & MOD_RM) {                                           
>                         priv->can.state = CAN_STATE_STOPPED;                     
>                         return;                                                  
>                 }                                                                
>                                                                                  
>                 /* reset chip */                                                 
>                 priv->write_reg(priv, SJA1000_MOD, MOD_RM);                      
>                 udelay(10);                                                      
>                 status = priv->read_reg(priv, SJA1000_MOD);                      
>         }                                                                        
>                                                                                  
>         netdev_err(dev, "setting SJA1000 into reset mode failed!\n");            
> }                                                      

Instrument this code to see what's going on.

> Now, what I don't understand at all:
> Removing the module and loading it again works.
> I don't get the error that setting the SJA1000 into reset mode failed,
> the register is only read once after loading the module,
> and sending/reading CAN frames from the bus after setting a proper
> bitrate works too....

Maybe the delay is to small for your big banging io interface.

> Any Ideas why the first initialization of the kernel module doesn't work?
> When is the probe function of the module actually called?

As soon as there is a matching driver//device combination on a bus.
Looking at your driver, it's racy. You should not do any hardware setup
in the init function.

> A completely other question: I wanted to use libsocketcan to check the
> state of the interface,
> bringing it up in case it's down, within my C/C++ Program.
> Is there a way to use this lib as a normal user? Maybe some group the
> user has to be in?

IIRC your process needs NET_ADMIN capabilities (CAP_NET_ADMIN). I
personally never used capabilities, but there are libcap and libcap-ng
(https://people.redhat.com/sgrubb/libcap-ng/), which might help.

Marc

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