netdev - Re: [PATCH RFC 0/2] stmmac: stand alone platform drivers

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Message-ID: <CAGhQ9Vx0DQf-HcqEiohFLrBJPBe5qYjLgXiH3qGx85fAruh8UQ@mail.gmail.com>
Date:	Tue, 12 May 2015 19:20:45 +0200
From:	Joachim Eastwood <manabian@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"peppe.cavallaro" <peppe.cavallaro@...com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 0/2] stmmac: stand alone platform drivers

On 8 May 2015 at 15:30, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 07 May 2015 20:19:23 Joachim Eastwood wrote:
>> Hi Arnd,
>>
>> I ran into some issue using a separate platform driver[1] for lpc1850-dwmac.
>>
>> My dts files looks like this.
>> mac: ethernet@...10000 {
>>         compatible = "nxp,lpc1850-dwmac", "snps,dwmac-3.611", "snps,dwmac";
>>         ...
>> }
>>
>> On boot the generic driver in stmmac_platform.c would grab the
>> device, matching on one of generic compat strings and thus blocking
>> the lpc1850-dwmac driver.
>>
>> By changing the build order in the Makefile (see patch 1) I managed
>> to get it working, but I am not sure that is a good solution(?).
>
> Changing the link order in the Makefile is an acceptable solution
> for managing initialization order in general, but I think it won't
> work here, because if your driver is a loadable module, the base
> driver would always be attached first.

That is true.

The setup/configuration I am testing doesn't use modules though and
the only way I can get the lpc1850-dwmac driver to probe the device is
to link the generic driver last.

>> Another fix would be to remove the generic compat strings from the
>> match table in stmmac_platform but there are some dts-files that
>> only have these compat strings.
>> See abilis_tb10x.dtsi and exynos5440.dtsi.
>
> Yes, that has a high risk of causing regressions.
>
>> I could also remove the generic compat strings from my dts file but
>> I am not sure that is good solution either. If more glue is
>> converted this would then be need in those dts files also.
>
> I think it would work if you move the generic strings into a separate
> module that is not the one providing the base support. In that case,
> the kernel should first try to use the driver that matches the first
> compatible string. Can you try that?

I have now created a generic dt dwmac driver which contain all compat
strings that doesn't have any match data. As long as this driver is
linked last this works for my built-in drivers configuration. I am not
able to test using modules because of my very limited rootfs. This is
a Cortex-M system after all.

I also converted all the other DT dwmac drivers and the entire patch
set can be found on:
https://github.com/manabian/linux-lpc

After I have done some more cleanups and added proper commit messages
I will put them on netdev again.


regards,
Joachim Eastwood
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