linux-kernel - Re: [PATCH 19/23] memory: omap-gpmc: Enclose macro statements in do-while

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Message-ID: <20200723101634.GD30472@kozik-lap>
Date:   Thu, 23 Jul 2020 12:16:34 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Olof Johansson <olof@...om.net>, arm-soc <arm@...nel.org>,
        SoC Team <soc@...nel.org>, Markus Mayer <mmayer@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Roger Quadros <rogerq@...com>,
        Tony Lindgren <tony@...mide.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC..." 
        <linux-mediatek@...ts.infradead.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        "open list:TEGRA ARCHITECTURE SUPPORT" <linux-tegra@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 19/23] memory: omap-gpmc: Enclose macro statements in
 do-while

On Thu, Jul 23, 2020 at 11:09:40AM +0200, Arnd Bergmann wrote:
> On Thu, Jul 23, 2020 at 9:39 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >
> > do-while is a preferred way for complex macros because of safety
> > reasons.  This fixes checkpatch error:
> >
> >     ERROR: Macros starting with if should be enclosed by a do - while
> >         loop to avoid possible if/else logic defects
> >
> > Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> 
> This is an improvement, but the macro still has other issues that
> are just as bad as the one you address:
> 
> - Using the # operator to avoid the "" in the invocation seems confusing

I guess it was useful for debugging.

> - it implicitly uses the 'cs' and 't' variables of the calling function instead
>   of passing them as arguments.

Actually another reason to convert it to just a function.

> - it calls 'return -1' in a function that otherwise uses errno-style
>   return codes, so this gets interpreted as EPERM "Operation not
>   permitted".

The users of this macro also do it (gpmc_cs_set_timings()) so this
wrong practice is consistent with the driver. :)

> 
> I would probably just open-code the entire thing and remove the
> macro like:
> 
> ret = 0;
> ret |= set_gpmc_timing_reg(cs, GPMC_CS_CONFIG2,  0,  3, 0, t->cs_on,
> GPMC_CD_FCLK, "cs_on");
> ret |= set_gpmc_timing_reg(cs, GPMC_CS_CONFIG2,  8,  12, 0,
> t->cs_rd_off, GPMC_CD_FCLK, "cs_rd_off");
> ret |= set_gpmc_timing_reg(cs, GPMC_CS_CONFIG2,  16,  20, 0,
> t->cs_wr_off, GPMC_CD_FCLK, "cs_wr_off);
> ...
> if (ret)
>      return -ENXIO;a

I like this approach because it also removes the 'return' from macro
which is not desired.

> 
> Of maybe leave the macro, but remove the if/return part and use
> the "ret |= GPMC_SET_ONE(...)" trick to avoid some of the problems.

I could probably then keep it as a function.  This would be the safest
and remove most of the problems here.

Best regards,
Krzysztof