linux-kernel - Re: [PATCH v3 31/36] serial: ucc_uart: stub out soft_uart_init for !CONFIG

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Date:   Mon, 4 Nov 2019 09:03:52 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Scott Wood <oss@...error.net>, linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 31/36] serial: ucc_uart: stub out soft_uart_init for
 !CONFIG_PPC32

On 01/11/2019 17.27, Christophe Leroy wrote:
> 
> 
> Le 01/11/2019 à 13:42, Rasmus Villemoes a écrit :
>> The Soft UART hack is only needed for some PPC-based SOCs. To allow
>> building this driver for non-PPC, guard soft_uart_init() and its
>> helpers by CONFIG_PPC32, and use a no-op soft_uart_init() otherwise.
> 
> I don't like too much ifdefs in C files, especially arch specific ifdefs
> in generic drivers.

Me neither. However,

> How do we get the QE version on ARM ?
> 
> Wouldn't it be cleaner to create a helper for getting the QE version,
> which would be defined in an arch specific header file, calling
> mfspr(SPRN_SVR) on powerpc and whatever needed on arm ?

First, that would mean we'd have to introduce "depends on PPC32 || ARM"
rather than drop "depends on PPC32". Second, the way the SOC version is
being used to construct the name of the microcode blob seems very
ppc-specific, so I don't see how one can reasonably define an interface
that would work for all architectures. But it's also kind of moot since
the ARM SOCs don't need this workaround.

IMO, having to add qe-specific code to arch/ is a cure worse than the
disease. I'd much rather add arch-specific code to qe.

Rasmus