linux-kernel - Re: [PATCH v3 net 2/2] net: stmmac: dwmac-imx: pause the TXC clock in fixed-link

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Message-ID: <ZMkBCGJrX/COB5+f@shell.armlinux.org.uk>
Date:   Tue, 1 Aug 2023 13:56:40 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Johannes Zink <j.zink@...gutronix.de>
Cc:     Shenwei Wang <shenwei.wang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Vinod Koul <vkoul@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        Simon Horman <simon.horman@...igine.com>,
        Andrew Halaney <ahalaney@...hat.com>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Wong Vee Khee <veekhee@...le.com>,
        Revanth Kumar Uppala <ruppala@...dia.com>,
        Jochen Henneberg <jh@...neberg-systemdesign.com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, imx@...ts.linux.dev,
        Frank Li <frank.li@....com>
Subject: Re: [PATCH v3 net 2/2] net: stmmac: dwmac-imx: pause the TXC clock
 in fixed-link

On Tue, Aug 01, 2023 at 02:47:46PM +0200, Johannes Zink wrote:
> Hi Shenwei,
> 
> thanks for your patch.
> 
> On 7/31/23 18:19, Shenwei Wang wrote:
> > When using a fixed-link setup, certain devices like the SJA1105 require a
> > small pause in the TXC clock line to enable their internal tunable
> > delay line (TDL).
> 
> If this is only required for some devices, is it safe to enforce this
> behaviour unconditionally for any kind of fixed link devices connected to
> the MX93 EQOS or could this possibly break for other devices?

This same point has been raised by Andrew Halaney in message-id
 <4govb566nypifbtqp5lcbsjhvoyble5luww3onaa2liinboguf@...ihys6vhrg>
and Fabio Estevam in message-id
 <CAOMZO5ANQmVbk_jy7qdVtzs3716FisT2c72W+3WZyu7FoAochw@...l.gmail.com>
but we don't seem to have any answer for it.

Also, the patch still uses wmb() between the write and the delay, and as
Will Deacon pointed out in his message, message-id
 <20230728153611.GH21718@...lie-the-truck>
this is not safe, yet still a new version was sent.

It seems the author of these patches is pretty resistant to comments,
and has shown that when I was requesting changes - it was an awful
struggle to get changes made. I'm now of the opinion that I really
can't be bothered to review these patches, precisely because feedback
is clearly not welcome or if welcome, apparently acted upon.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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