RE: [EXTERNAL] Re: [PATCH v2 0/5] Fix prestera driver fail to probe twice

[Elad Nachman]

Hi Andrew,

We have made internal technical review of the issues you have raised (return version API, try to get version API before starting to initialize and load the firmware, clear configuration API) versus the delay saved (almost 30 seconds minus several seconds to perform and complete the API calls) - around 20 seconds or so.

Existing customers we have talked to seem to be able to cope with the existing delay.

Unfortunately, the amount of coding and testing involved with saving these 20 seconds or so is beyond our available development manpower at this specific point in time.

Unfortunately, we will have to defer making the development you have requested to a later period in time.

Elad.


> -----Original Message-----
> From: Andrew Lunn <andrew@xxxxxxx>
> Sent: Sunday, March 24, 2024 5:25 PM
> To: Elad Nachman <enachman@xxxxxxxxxxx>
> Cc: Taras Chornyi <taras.chornyi@xxxxxxxxxxx>; davem@xxxxxxxxxxxxx;
> edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx;
> kory.maincent@xxxxxxxxxxx; thomas.petazzoni@xxxxxxxxxxx;
> miquel.raynal@xxxxxxxxxxx; przemyslaw.kitszel@xxxxxxxxx;
> dkirjanov@xxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [EXTERNAL] Re: [PATCH v2 0/5] Fix prestera driver fail to probe
> twice
> 
> > > > Originally, the pain point for Kory was the rmmod + insmod
> > > > re-probing failure, Which is only fixed by the first two commits,
> > > > so I see little point in submitting 3-5 alone, Without fixing Kory's
> problem.
> > >
> > > I thought Kory's problem was actually EPROBE_DEFER? The resources
> > > needed for the PoE are not available, so probing the switch needs to
> > > happen again later, when PoE can get the resources it needs.
> >
> > No, the PoE is the general high level application where he noted the
> problem.
> > There is no PoE code nor special PoE resources in the Prestera driver.
> 
> So here is Köry email:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__lore.kernel.org_netdev_20240208101005.29e8c7f3-40kmaincent-2DXPS-
> 2D13-2D7390_T_-
> 23mb898bb2a4bf07776d79f1a19b6a8420716ecb4a3&d=DwIDAw&c=nKjWec2
> b6R0mOyPaz7xtfQ&r=eTeNTLEK5-
> TxXczjOcKPhANIFtlB9pP4lq9qhdlFrwQ&m=SD1MhKC11sFmp4Q8l76N_DgGdac
> 4aMCTdPsa7Pofb73HEqAGtJ-1p0-
> etIyyldC7&s=VWat9LPub52H3nUez4itmkpuMipnYD3Ngn-paFC9wd4&e=
> 
> I don't see why the prestera needs to be involved in PoE itself. It is just a MAC.
> PoE happens much lower down in the network stack. Same as Prestera uses
> phylink, it does not need to know about the PHYs or the SFP modules, phylink
> manages them, not prestera.
> 
> > The problem was caused because the module exit was lacking the so
> > called "switch HW reset" API call which would cause the firmware to
> > exit to the firmware loader on the firmware CPU, and move to the state
> > in the state machine when it can receive new firmware from the host
> > CPU (running the Prestera switchDev driver).
> >
> > >
> > > But if that is going to take 30 seconds, i'm not sure we can call
> > > EPROBE_DEFER solved.
> > >
> > > The later patches are pretty simple, don't need discussion, so could
> > > be merged. However, i think we need to explore different possible
> > > solutions for firmware {re}loading.
> > >
> > > > The problem is not with the hardware, but with the existing
> > > > firmware code on the Firmware cpu, most probably secure-boot
> > > > protected, which lacks the ABIs to report to The kernel what is
> > > > loaded, what version, what
> > > state, etc.
> > >
> > > Can you at least tell if it is running firmware?
> >
> > There is no existing API/ABI for that.
> 
> Do you at least have the ability to determine if an API call exists or not? It
> sounds like your firmware needs extending to support returning the version.
> If the API is missing, you know it is 4.1 or older. If it does exist, it will return
> 4.2 or higher.
> 
> > > Can you explain the boot in a bit more detail. Are you saying it
> > > could be running an old firmware when the driver first loads? So you
> > > need to hit it with
> >
> > Exactly.
> >
> > > a reset in order to load the firmware for /lib/firmware, which might
> > > be newer than what it is already running?
> >
> > Right. And there is also the configuration. There is no telling what
> > kind of Configuration the existing firmware is running. Just using the
> > existing firmware Will lead to the situation where Linux kernel side
> > will report certain configuration (via ip link / ip addr / tc , etc.) but the
> firmware configuration is completely different.
> 
> Well, during probe and -EPRODE_DEFER, linux has no configuration, since the
> driver failed to probe. However, for a rmmod/modprobe, the firmware could
> have stale configuration. However pretty much every device i've come across
> has the concept of a software reset which clears out the configuration. Seems
> to be something else your firmware is missing.
> 
> 	Andrew