Re: [dpdk-dev] [PATCH] net/thunderx: sync mailbox definitions with Linux PF driver

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Wed, Mar 22, 2017 at 10:33:14AM +0000, Ferruh Yigit wrote:
> On 3/22/2017 9:39 AM, Jerin Jacob wrote:
> > On Tue, Mar 21, 2017 at 02:53:29PM +0000, Ferruh Yigit wrote:
> >> On 3/21/2017 2:38 PM, Jerin Jacob wrote:
> >>> On Tue, Mar 21, 2017 at 02:31:41PM +0000, Ferruh Yigit wrote:
> >>>> On 3/20/2017 2:10 PM, Jerin Jacob wrote:
> >>>>> - bgx_link_status mbox definition was changed in Linux
> >>>>> commit 1cc702591bae ("net: thunderx: Add ethtool support")
> >>>>> - NIC_MBOX_MSG_RES_BIT related changes were never part of Linux PF driver
> >>>>>
> >>>>> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> >>>>
> >>>> <...>
> >>>>
> >>>>> @@ -157,6 +151,7 @@ struct rss_cfg_msg {
> >>>>>  /* Physical interface link status */
> >>>>>  struct bgx_link_status {
> >>>>>  	uint8_t    msg;
> >>>>> +	uint8_t    mac_type;
> >>>>
> >>>> Hi Jerin,
> >>>>
> >>>> Is this modification related to this patch?
> >>>
> >>> Yes Ferruh.
> >>>
> >>> This was related to the following section in git log comment.
> >>> ----
> >>> - bgx_link_status mbox definition was changed in Linux
> >>> commit 1cc702591bae ("net: thunderx: Add ethtool support") 
> >>> ---
> >>
> >> I see now, thanks. Since this is to sync with Linux PF, shouldn't it be
> >> used in driver, perhaps something like in Linux driver:
> >> "nic->mac_type = mbx.link_status.mac_type"
> >>
> >> What is the point of just adding definition without using it?
> > 
> > That is to keep "link_up"(next element in the struct bgx_link_status) points
> > to correct location after the kernel change. 
> 
> I see, thanks. It is pity that new field added into middle (or beginning
> if you exclude msg) of the struct.
> 
> > I thought about, the backward
> > compatibility with older kernel, Is it OK to use linux/version.h in PMD drivers
> > to detect the kernel version?
> 
> Technically possible, but kernel version check has its problems:
> 1) Adds maintenance cost, which gets worse by time.
> 2) If added a compile time check, it creates binary distribution
> problems, distro guys may not like PMD has dependency to kernel.
> 3) It will create dependency to Linux, assuming Thunderx PMD supported
> in FreeBSD
> 
> > drivers/net/mlx5/mlx5_ethdev.c has similar
> > kernel detection mechanism to make it backward compatible.
> 
> Yes, at least mlx added a dynamic check which prevents above issue 2.
> 
> > If there are no issue with such approach, I will roll out a new revision.
> 
> Is there any way to detect this dynamically, first things I can think of:
> - Any mbx versioning to rely on?
> - Any common NIC user header file provided by kernel, to use in DPDK, to
> prevent any this kind of issues in the future?
> - Any msg size value to detect if mac_type exists or not?
> - Heuristic approach to other values to detect mac_type existence?

Thanks for sharing the options.
First three options wont work. Heuristic option is pretty limited,
mac_type value can also be 0 or 1(same as link_up)
So I think, The best option now to use the patch as is(without kernel
check).
What do you think?

> 
> > 
> > 
> >>
> >>>
> >>>
> >>>>
> >>>>>  	uint8_t    link_up;
> >>>>>  	uint8_t    duplex;
> >>>>>  	uint32_t   speed;
> >>>>>
> >>>>
> >>
>