netdev - Re: stmmac / meson8b-dwmac

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Date:   Fri, 1 Mar 2019 09:23:22 +0000
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     Simon Huelck <simonmail@....de>,
        Jose Abreu <jose.abreu@...opsys.com>,
        Sebastian Gottschall <s.gottschall@...media-net.de>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     <linux-amlogic@...ts.infradead.org>, <Gpeppe.cavallaro@...com>,
        <alexandre.torgue@...com>,
        Emiliano Ingrassia <ingrassia@...genesys.com>,
        <netdev@...r.kernel.org>
Subject: Re: stmmac / meson8b-dwmac

Hi Simon,

On 2/27/2019 7:02 PM, Simon Huelck wrote:
> Hi,
> 
> 
> the thing is , that im not a stmmac developer. Yes , maybe i can bissect
> it and yes you are lucky since im a C-developer since a long time for
> embedded systems.
> 
> The problem is that i dont understand the structure of stmmac and im not
> aware of any documentation about the driver structure nor the underlying
> ethernet hardware ( even though im used to ethernet hardware in embedded
> environment ). So how shall i recognize the relevant change between
> 4.14.29 and 5.0rc8 ?
> 
> 
> Is it in the DTS/DTB, wrong hardware description ? Is it in the code ?
> how is the duplex hardware working on this piece ?
> 
> I can try to support you the best i can, but i have little chances to
> analyze it myself. At which measurements / counters is it possible to
> see that duplex is fully working ?  Why did even the non-duplex
> bandwidth regress from 900MBits to 650 ? Why is that 650 MBits dividing
> up to TX and RX in summary when doing duplex ? Why is TX not starving in
> duplex but RX ?
> 
> From my point of view should be the following things given:
> - the non duplex bandwidth should be somewhere around 900MBits , the HW
> is capable of that
> - TX should not influence RX or vice versa in duplex
> - the duplex bandwidth should be 900MBits in both directions ( maybe a
> bit asymetric when buffers in both dirs are not same )
> 
> I guess we need some profiling on stmmac and ( at least i need ) more
> knowledge of the hardware and stmmac itself. Can someone point me to the
> driver documentation, describing the functions in the code and the
> structure ? How can i profile stmmac ( usually im using hardware / JTAG
> debuggers at work, but here @home i got nothing like that )
> 
> So how do we continue ?

When I said bissect I was meaning GIT Bissect [1]. You shouldn't
need any development background for this. You just have to start
bissect, compile, test and check if commit is good or not.

I'm not very familiar with this feature but I think you can
bissect pretty fast if you say you just want stmmac commits,
check ("Cutting down bisection by giving more parameters to
bisect start") on previous link ... In your case it would be
stmmac changes, dts, and phy.

[1] https://git-scm.com/docs/git-bisect

Thanks,
Jose Miguel Abreu