netdev - RE: [PATCH 1/2] stmmac: introduce flag to dynamically disable TX offload for rockchip devices

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Date:   Tue, 2 Apr 2019 11:53:27 +0000
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     Robin Murphy <robin.murphy@....com>,
        Jose Abreu <jose.abreu@...opsys.com>,
        Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
        Heiko Stübner <heiko@...ech.de>,
        Christoph Müllner 
        <christoph.muellner@...obroma-systems.com>
CC:     "Leonidas P. Papadakos" <papadakospan@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Klaus Goger <klaus.goger@...obroma-systems.com>
Subject: RE: [PATCH 1/2] stmmac: introduce flag to dynamically disable TX
 offload for rockchip devices

From: Robin Murphy <robin.murphy@....com>
Date: Tue, Apr 02, 2019 at 12:49:36

> On 02/04/2019 08:59, Jose Abreu wrote:
> > From: Philipp Tomsich <philipp.tomsich@...obroma-systems.com>
> > Date: Mon, Apr 01, 2019 at 20:12:21
> > 
> >> + Christoph.
> >>
> >>> On 01.04.2019, at 21:06, Heiko Stübner <heiko@...ech.de> wrote:
> >>>
> >>> Am Montag, 1. April 2019, 20:54:45 CEST schrieb Robin Murphy:
> >>>> On 01/04/2019 19:18, Leonidas P. Papadakos wrote:
> >>>>> From: =?UTF-8?q?Kamil=20Trzci=C5=84ski?= <ayufan@...fan.eu>
> >>>>>
> >>>>> Some rockchip boards exhibit an issue where tx checksumming does not 
> work
> >> with
> >>>>> packets larger than 1498.
> >>>>
> >>>> Is it really a board-level problem? I'm no networking expert, but the
> >>>> nature of the workaround suggests this is more likely to be some
> >>>> inherent limitation of the IP block in the SoC, rather than something to
> >>>> do with how the external pins get wired up. Does anyone have an RK3328
> >>>> or RK3399 board that provably *does* checksum large packets correctly?
> >>>
> >>> I don't have that many rk3399-boards with actual ethernet and even only
> >>> the rock64 from rk3328-land, but at least my rk3399-firefly also seems
> >>> affected by this.
> >>>
> >>> But so far the rk3399-puma board from Theobroma did not show that 
> ethernet
> >>> issue for me, so I've added two Theobroma people who may or may not tell
> >>> if they've also seen that issue.
> >>>
> >>>>
> >>>>> This is bad for network stability.
> >>>>>
> >>>>> The previous approach was using force_thresh_dma_mode in the board dts,
> >> which
> >>>>> does more than we need.
> >>>>
> >>>> If indeed it is a SoC-level thing (or at least we want to treat it as
> >>>> such), then couldn't we just hang it off the existing SoC-specific
> >>>> compatibles in dwmac-rk.c and avoid the need for a new DT property at
> >>>> all? After all, that's precisely why SoC-specific compatibles are a
> >>>> thing in the first place.
> >>>>
> > 
> > This can happen when FIFO size + PBL settings are not big enough for COE.
> > 
> > Can you please share the above settings ?
> 
> Can the FIFO size be discovered by dumping registers, or does someone 
> from Rockchip need to look up the IP configuration details?
> 
> FWIW, taking a look at the RK3399 TRM, this (p788) jumps out:
> 
> "PBL
> ...
> For TxFIFO, valid PBL range in full duplex mode and duplex mode is
> 128 or less.
> For RxFIFO, valid PBL range in full duplex mode is all."
> 
> 
> Does that suggest that it's worth fiddling with the "snps,txpbl" value 
> in DT?

Yes, please try with PBL = 0x1 and no-pbl-x8. Performance will be lower
but at least we will know if that’s the cause.

Thanks,
Jose Miguel Abreu