linux-kernel - Re: [PATCH v13 1/2] ACPI / APEI: Add a notifier chain for unknown (vendor) CPER records

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Date:   Fri, 24 Jul 2020 07:53:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Shiju Jose <shiju.jose@...wei.com>
Cc:     "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "bp@...en8.de" <bp@...en8.de>,
        "james.morse@....com" <james.morse@....com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
        "zhangliguang@...ux.alibaba.com" <zhangliguang@...ux.alibaba.com>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@...wei.com>,
        "jroedel@...e.de" <jroedel@...e.de>,
        Linuxarm <linuxarm@...wei.com>,
        yangyicong <yangyicong@...wei.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        tanxiaofei <tanxiaofei@...wei.com>
Subject: Re: [PATCH v13 1/2] ACPI / APEI: Add a notifier chain for unknown
 (vendor) CPER records

On Fri, Jul 24, 2020 at 09:00:41AM +0000, Shiju Jose wrote:
> >-----Original Message-----
> >From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> >Sent: 24 July 2020 00:21
> >To: Shiju Jose <shiju.jose@...wei.com>
> >Cc: linux-acpi@...r.kernel.org; linux-pci@...r.kernel.org; linux-
> >kernel@...r.kernel.org; rjw@...ysocki.net; bp@...en8.de;
> >james.morse@....com; lenb@...nel.org; tony.luck@...el.com;
> >dan.carpenter@...cle.com; zhangliguang@...ux.alibaba.com;
> >andriy.shevchenko@...ux.intel.com; Wangkefeng (OS Kernel Lab)
> ><wangkefeng.wang@...wei.com>; jroedel@...e.de; Linuxarm
> ><linuxarm@...wei.com>; yangyicong <yangyicong@...wei.com>; Jonathan
> >Cameron <jonathan.cameron@...wei.com>; tanxiaofei
> ><tanxiaofei@...wei.com>
> >Subject: Re: [PATCH v13 1/2] ACPI / APEI: Add a notifier chain for unknown
> >(vendor) CPER records
> >
> >On Wed, Jul 22, 2020 at 11:39:51AM +0100, Shiju Jose wrote:
> >> CPER records describing a firmware-first error are identified by GUID.
> >> The ghes driver currently logs, but ignores any unknown CPER records.
> >> This prevents describing errors that can't be represented by a
> >> standard entry, that would otherwise allow a driver to recover from an
> >error.
> >> The UEFI spec calls these 'Non-standard Section Body' (N.2.3 of
> >> version 2.8).
> >
> >> +#ifdef CONFIG_ACPI_APEI_GHES
> >> +/**
> >> + * ghes_register_vendor_record_notifier - register a notifier for
> >> +vendor
> >> + * records that the kernel would otherwise ignore.
> >> + * @nb: pointer to the notifier_block structure of the event handler.
> >> + *
> >> + * return 0 : SUCCESS, non-zero : FAIL  */ int
> >> +ghes_register_vendor_record_notifier(struct notifier_block *nb);
> >> +
> >> +/**
> >> + * ghes_unregister_vendor_record_notifier - unregister the previously
> >> + * registered vendor record notifier.
> >> + * @nb: pointer to the notifier_block structure of the vendor record
> >handler.
> >> + */
> >> +void ghes_unregister_vendor_record_notifier(struct notifier_block
> >> +*nb); #else static inline int
> >> +ghes_register_vendor_record_notifier(struct notifier_block *nb) {
> >> +	return -ENODEV;
> >> +}
> >> +
> >> +static inline void ghes_unregister_vendor_record_notifier(struct
> >> +notifier_block *nb) { }
> >
> >If you made CONFIG_PCIE_HISI_ERR depend on CONFIG_ACPI_APEI_GHES,
> >you'd be able to get rid of these stubs, wouldn't you?  It doesn't
> >look like there's any point in building pcie-hisi-error.c at all
> >unless CONFIG_ACPI_APEI_GHES is enabled.
>
> The stub is added because this interface is expected to use by the
> other drivers as well.  Some drivers may not want add the build
> depend on the CONFIG_ACPI_APEI_GHES if the error reporting has less
> priority in the driver.  However we can add dependency on
> CONFIG_ACPI_APEI_GHES for building pcie-hisi-error.c.  

The usual route is to add stubs when they're needed, not just in
anticipation of some need that may never materialize.