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

From: Guenter Roeck
Date: Thu Sep 09 2021 - 10:53:38 EST

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

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 ?