From: Vladimir Oltean <firstname.lastname@example.org> To: Florian Fainelli <email@example.com> Cc: firstname.lastname@example.org, email@example.com, "David S. Miller" <firstname.lastname@example.org>, Jakub Kicinski <email@example.com>, Murali Krishna Policharla <firstname.lastname@example.org>, Vladimir Oltean <email@example.com>, "open list:BROADCOM SYSTEMPORT ETHERNET DRIVER" <firstname.lastname@example.org>, open list <email@example.com> Subject: Re: [PATCH net] net: systemport: set dev->max_mtu to UMAC_MAX_MTU_SIZE Date: Tue, 22 Dec 2020 00:25:34 +0200 [thread overview] Message-ID: <20201221222534.ln4onsjpryqzzfqq@skbuf> (raw) In-Reply-To: <firstname.lastname@example.org> On Mon, Dec 21, 2020 at 01:49:03PM -0800, Florian Fainelli wrote: > On 12/18/2020 1:17 PM, Florian Fainelli wrote: > >>>>>>> SYSTEMPORT Lite does not actually validate the frame length, so setting > >>>>>>> a maximum number to the buffer size we allocate could work, but I don't > >>>>>>> see a reason to differentiate the two types of MACs here. > >>>>>> > >>>>>> And if the Lite doesn't validate the frame length, then shouldn't it > >>>>>> report a max_mtu equal to the max_mtu of the attached DSA switch, plus > >>>>>> the Broadcom tag length? Doesn't the b53 driver support jumbo frames? > >>>>> > >>>>> And how would I do that without create a horrible layering violation in > >>>>> either the systemport driver or DSA? Yes the b53 driver supports jumbo > >>>>> frames. > >>>> > >>>> Sorry, I don't understand where is the layering violation (maybe it doesn't > >>>> help me either that I'm not familiar with Broadcom architectures). > >>>> > >>>> Is the SYSTEMPORT Lite always used as a DSA master, or could it also be > >>>> used standalone? What would be the issue with hardcoding a max_mtu value > >>>> which is large enough for b53 to use jumbo frames? > >>> > >>> SYSTEMPORT Lite is always used as a DSA master AFAICT given its GMII > >>> Integration Block (GIB) was specifically designed with another MAC and > >>> particularly that of a switch on the other side. > >>> > >>> The layering violation I am concerned with is that we do not know ahead > >>> of time which b53 switch we are going to be interfaced with, and they > >>> have various limitations on the sizes they support. Right now b53 only > >>> concerns itself with returning JMS_MAX_SIZE, but I am fairly positive > >>> this needs fixing given the existing switches supported by the driver. > >> > >> Maybe we don't need to over-engineer this. As long as you report a large > >> enough max_mtu in the SYSTEMPORT Lite driver to accomodate for all > >> possible revisions of embedded switches, and the max_mtu of the switch > >> itself is still accurate and representative of the switch revision limits, > >> I think that's good enough. > > > > I suppose that is fair, v2 coming, thanks! > > I was going to issue a v2 for this patch, but given that we don't > allocate buffers larger than 2KiB and there is really no need to > implement ndo_change_mtu(), is there really a point not to use > UMAC_MAX_MTU_SIZE for both variants of the SYSTEMPORT MAC? After your first reply that "the Lite doesn't validate the frame length", I was under the impression that it is sufficient to declare a larger max_mtu such as JMS_MAX_SIZE and 9K jumbo frames would just work. But with the current buffer allocation in bcm_sysport_rx_refill it clearly wouldn't. A stupid confusion really. So yeah, sorry for having you resend a v2 with no change. If it helps you could add to the patch: Reviewed-by: Vladimir Oltean <email@example.com> Thanks again for explaining.
next prev parent reply other threads:[~2020-12-21 22:26 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-18 17:38 Florian Fainelli 2020-12-18 20:24 ` Vladimir Oltean 2020-12-18 20:30 ` Florian Fainelli 2020-12-18 20:52 ` Vladimir Oltean 2020-12-18 20:54 ` Florian Fainelli 2020-12-18 21:02 ` Vladimir Oltean 2020-12-18 21:08 ` Florian Fainelli 2020-12-18 21:14 ` Vladimir Oltean 2020-12-18 21:17 ` Florian Fainelli 2020-12-21 21:49 ` Florian Fainelli 2020-12-21 22:25 ` Vladimir Oltean [this message] 2020-12-21 22:55 ` Florian Fainelli
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