Re: [PATCH 1/2] net: pegasus: convert control messages to the new send/recv scheme.

[Petko Manolov <petkan@nucleusys.com>]

On 20-09-26 07:44:57, Greg KH wrote:
> On Fri, Sep 25, 2020 at 07:01:59PM +0300, Petko Manolov wrote:
> > From: Petko Manolov <petko.manolov@konsulko.com>
> > 
> > Move all control transfers to safer usb_control_msg_send/recv() API.
> 
> This says _what_ the patch does, but we can see that from the diff.  You
> should describe _why_ we are doing what we are doing, so that everyone
> understands the need for the change.

Didn't want to parrot the reason for usb_control_msg_send/recv() existence, but 
i guess you're right.  5 years from now i would not remember anything. :)

> >  static int set_register(pegasus_t *pegasus, __u16 indx, __u8 data)
> >  {
> > -	u8 *buf;
> > -	int ret;
> > -
> > -	buf = kmemdup(&data, 1, GFP_NOIO);
> > -	if (!buf)
> > -		return -ENOMEM;
> > -
> > -	ret = usb_control_msg(pegasus->usb, usb_sndctrlpipe(pegasus->usb, 0),
> > -			      PEGASUS_REQ_SET_REG, PEGASUS_REQT_WRITE, data,
> > -			      indx, buf, 1, 1000);
> > -	if (ret < 0)
> > -		netif_dbg(pegasus, drv, pegasus->net,
> > -			  "%s returned %d\n", __func__, ret);
> > -	kfree(buf);
> > -	return ret;
> > +	return usb_control_msg_send(pegasus->usb, 0, PEGASUS_REQ_SET_REG,
> > +			            PEGASUS_REQT_WRITE, data, indx, &data, 1,
> > +				    1000, GFP_NOIO);
> >  }
> 
> Again, why isn't set_register() now rewritten to just be:
> 
> static int set_register(pegasus_t *pegasus, __u16 indx, __u8 data)
> {
> 	return set_registers(pegasus, indx, 1, data);
> }
> 
> Much easier to show that it's all converted properly :)

There's a catch - adm8511-based devices can only write to a single register via 
specific control request.  This request expects the register number in wIndex 
and the value in wValue.  A bit of a brain fart which is fixed in adm8515.

Admittedly, I could open code set_register() and avoid a kmemdup() call since in 
this case 'data' is going to be NULL.  However, set_register() isn't heavily 
used, except for the setup phase, so i went for the prettier/simpler approach.  
Which reminds me that i should put a comment explaining why is that.


cheers,
Petko