linux-kernel - Re: [PATCH] of/base: Fix PowerPC address parsing hack

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Message-ID: <CACxGe6s0CXL2oRKCLhzzycOKWJStxdZsc1pn_X8fLuAqCguBMA@mail.gmail.com>
Date:	Thu, 13 Nov 2014 12:44:19 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Rob Herring <robherring2@...il.com>,
	Olof Johansson <olof@...om.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	linuxppc-dev <linuxppc-dev@...abs.org>
Subject: Re: [PATCH] of/base: Fix PowerPC address parsing hack

On Thu, Nov 13, 2014 at 12:45 AM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> What about this one instead ? I want to cache it because that function
> can be called quite a while and doing two additional property lookup
> and string compares every time might hurt some platforms.
>
> ----
>
> We have a historical hack that treats missing ranges properties as the
> equivalent of an empty one. This is needed for ancient PowerMac "bad"
> device-trees, and shouldn't be enabled for any other PowerPC platform,
> otherwise we get some nasty layout of devices in sysfs or even
> duplication when a set of otherwise identically named devices is
> created multiple times under a different parent node with no ranges
> property.
>
> This fix is needed for the PowerNV i2c busses to be exposed properly
> and will fix a number of other embedded cases.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> CC: <stable@...r.kernel.org>

How far back does this need to go? I assume I need to get this in for v3.18.

>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index e371825..5eae0cd 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -403,6 +403,17 @@ static struct of_bus *of_match_bus(struct device_node *np)
>         return NULL;
>  }
>
> +static int of_empty_ranges_quirk(void)
> +{
> +       /* To save cycles, we cache the result */
> +       static int quirk_state = -1;
> +

if (IS_ENABLED(CONFIG_POWERPC)) {

> +       if (quirk_state < 0)
> +               quirk_state = of_machine_is_compatible("Power Macintosh") ||
> +                       of_machine_is_compatible("MacRISC");
> +       return quirk_state;

}
return 0;

So it gets compiled out for non powerpc.

> +}
> +
>  static int of_translate_one(struct device_node *parent, struct of_bus *bus,
>                             struct of_bus *pbus, __be32 *addr,
>                             int na, int ns, int pna, const char *rprop)
> @@ -428,12 +439,10 @@ static int of_translate_one(struct device_node *parent, struct of_bus *bus,
>          * This code is only enabled on powerpc. --gcl
>          */
>         ranges = of_get_property(parent, rprop, &rlen);
> -#if !defined(CONFIG_PPC)
> -       if (ranges == NULL) {
> +       if (ranges == NULL && !of_empty_ranges_quirk()) {
>                 pr_err("OF: no ranges; cannot translate\n");
>                 return 1;
>         }
> -#endif /* !defined(CONFIG_PPC) */
>         if (ranges == NULL || rlen == 0) {
>                 offset = of_read_number(addr, na);
>                 memset(addr, 0, pna * 4);
>
>
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