Re: [PATCH] net: 6pack: Fix tx timeout and slot time

[Guenter Roeck]

On 9/9/21 4:34 AM, David Miller wrote:
> From: Guenter Roeck <linux@xxxxxxxxxxxx>
> Date: Wed,  8 Sep 2021 20:57:43 -0700
>
> > tx timeout and slot time are currently specified in units of HZ.
> > On Alpha, HZ is defined as 1024. When building alpha:allmodconfig,
> > this results in the following error message.
> >
> > drivers/net/hamradio/6pack.c: In function 'sixpack_open':
> > drivers/net/hamradio/6pack.c:71:41: error:
> > 	unsigned conversion from 'int' to 'unsigned char'
> > 	changes value from '256' to '0'
> >
> > In the 6PACK protocol, tx timeout is specified in units of 10 ms
> > and transmitted over the wire. Defining a value dependent on HZ
> > doesn't really make sense. Assume that the intent was to set tx
> > timeout and slot time based on a HZ value of 100 and use constants
> > instead of values depending on HZ for SIXP_TXDELAY and SIXP_SLOTTIME.
> >
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > No idea if this is correct or even makes sense. Compile tested only.
>
> These are timer offsets so they have to me HZ based.  Better to make the
> structure members unsigned long, I think.

Hmm, ok. Both tx_delay and slottime are updated in sp_encaps(), though,
from data in the transmit buffer. The KISS protocol description states
that the values are in units of 10ms; that is where my assumption
came from.

Command        Function         Comments
   0           Data frame       The  rest  of the frame is data to
                                be sent on the HDLC channel.

   1           TXDELAY          The next  byte  is  the  transmitter
                                keyup  delay  in  10 ms units.
                		The default start-up value is 50
                                (i.e., 500 ms).

   2           P                The next byte  is  the  persistence
                                parameter,  p, scaled to the range
                                0 - 255 with the following
                                formula:

                                         P = p * 256 - 1

                                The  default  value  is  P  =  63
                                (i.e.,  p  =  0.25).

   3           SlotTime         The next byte is the slot interval
                                in 10 ms units.
                                The default is 10 (i.e., 100ms).

But then slottime is indeed used with jiffies, which is odd.

tx_delay is used (before it is updated) in encode_sixpack()
and added to a character buffer. I thought that was the value sent
on the wire (which would again be supposed to be in 10ms units).
I don't see where else it is used, but I may be missing it.
That means though it can not easily be changed to anything
but unsigned char.

Anyway, I am inclined to just mark the protocol as dependent on
!ALPHA. Would you accept that ?

Thanks,
Guenter