From: Florian Fainelli <firstname.lastname@example.org> To: Vladimir Oltean <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: Mon, 21 Dec 2020 13:49:03 -0800 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> 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? -- Florian
next prev parent reply other threads:[~2020-12-21 21:50 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 [this message] 2020-12-21 22:25 ` Vladimir Oltean 2020-12-21 22:55 ` Florian Fainelli
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