linux-kernel - Re: [PATCH v2 1/4] mmc: sdhci-of-aspeed: Fix link failure for SPARC

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Date:   Mon, 02 Sep 2019 14:56:38 +0930
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Joel Stanley" <joel@....id.au>, "Arnd Bergmann" <arnd@...db.de>
Cc:     linux-mmc <linux-mmc@...r.kernel.org>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        "Ulf Hansson" <ulf.hansson@...aro.org>,
        "OpenBMC Maillist" <openbmc@...ts.ozlabs.org>,
        "Linux ARM" <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "kbuild test robot" <lkp@...el.com>
Subject: Re: [PATCH v2 1/4] mmc: sdhci-of-aspeed: Fix link failure for SPARC

On Mon, 2 Sep 2019, at 13:42, Joel Stanley wrote:
> On Mon, 2 Sep 2019 at 03:58, Andrew Jeffery <andrew@...id.au> wrote:
> >
> > Resolves the following build error reported by the 0-day bot:
> >
> >     ERROR: "of_platform_device_create" [drivers/mmc/host/sdhci-of-aspeed.ko] undefined!
> >
> > SPARC does not set CONFIG_OF_ADDRESS so the symbol is missing. Guard the
> > callsite to maintain build coverage for the rest of the driver.
> >
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Signed-off-by: Andrew Jeffery <andrew@...id.au>
> > ---
> >  drivers/mmc/host/sdhci-of-aspeed.c | 38 ++++++++++++++++++++----------
> >  1 file changed, 25 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-of-aspeed.c b/drivers/mmc/host/sdhci-of-aspeed.c
> > index d5acb5afc50f..96ca494752c5 100644
> > --- a/drivers/mmc/host/sdhci-of-aspeed.c
> > +++ b/drivers/mmc/host/sdhci-of-aspeed.c
> > @@ -224,10 +224,30 @@ static struct platform_driver aspeed_sdhci_driver = {
> >         .remove         = aspeed_sdhci_remove,
> >  };
> >
> > -static int aspeed_sdc_probe(struct platform_device *pdev)
> > -
> > +static int aspeed_sdc_create_sdhcis(struct platform_device *pdev)
> >  {
> > +#if defined(CONFIG_OF_ADDRESS)
> 
> This is going to be untested code forever, as no one will be running
> on a chip with this hardware present but OF_ADDRESS disabled.
> 
> How about we make the driver depend on OF_ADDRESS instead?

Testing is split into two pieces here: compile-time and run-time.
Clearly the run-time behaviour is going to be broken on configurations
without CONFIG_OF_ADDRESS (SPARC as mentioned), but I don't think
that means we shouldn't allow it to be compiled in that case
(e.g. CONFIG_COMPILE_TEST performs a similar role).

With respect to compile-time it's possible to compile either path as
demonstrated by the build failure report.

Having said that there's no reason we  couldn't do what you suggest,
just it wasn't the existing solution pattern for the problem (there are
several other drivers that suffered the same bug that were fixed in the
style of this patch). Either way works, it's all somewhat academic.
Your suggestion is more obvious in terms of correctness, but this
patch is basically just code motion (the only addition is the `#if`/
`#endif` lines over what was already there if we disregard the
function declaration/invocation). I'll change it if there are further
complaints and a reason to do a v3.

Andrew