linux-kernel - Re: [PATCH v13 7/9] ACPI: Translate the I/O range of non-MMIO devices before scanning

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Message-ID: <20180215123642.GA28256@e107981-ln.cambridge.arm.com>
Date:   Thu, 15 Feb 2018 12:36:42 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     John Garry <john.garry@...wei.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Olof Johansson <olof@...om.net>,
        Dann Frazier <dann.frazier@...onical.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Rob Herring <robh@...nel.org>, Joe Perches <joe@...ches.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>, Corey Minyard <minyard@....org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v13 7/9] ACPI: Translate the I/O range of non-MMIO
 devices before scanning

On Thu, Feb 15, 2018 at 12:47:25PM +0100, Rafael J. Wysocki wrote:
> On Thu, Feb 15, 2018 at 12:19 PM, John Garry <john.garry@...wei.com> wrote:
> >> Nothing apart from only being used by arm64 platforms today, which is
> >> circumstantial.
> >>
> >>>
> >>> I understand you need to find a place to add the:
> >>>
> >>> acpi_indirect_io_scan_init()
> >>>
> >>> to be called from core ACPI code because ACPI can't handle probe
> >>> dependencies in any other way but other than that this patch is
> >>> a Hisilicon ACPI driver - there is nothing generic in it (or at
> >>> least there are no standard bindings to make it so).
> >>>
> >>> Whether a callback from ACPI core code (acpi_scan_init()) to a driver
> >>> specific hook is sane or not that's the question and the only reason
> >>> why you want to add this in drivers/acpi/arm64 rather than, say,
> >>> drivers/bus (as you do for the DT driver).
> >>>
> >>> I do not know Rafael's opinion on the above, I would like to help
> >>> you make forward progress but please understand my concerns, mostly
> >>> on FW side.
> >>>
> >>
> >> I did mention an alternative in my "ping" in v12 patch 7/9 (Feb 1), but
> >> no response to this specific note so I kept on the same path.
> >>
> >> Here's what I then wrote:
> >> "I think another solution - which you may prefer - is to avoid adding
> >> this scan handler (and all this other scan code) and add a check like
> >> acpi_is_serial_bus_slave() [which checks the device parent versus a list
> >> of known indirectIO hosts] to not enumerate these children, and do it
> >> from the LLDD host probe instead (https://lkml.org/lkml/2017/6/16/250)"
> >>
> >
> > Hi Rafael, Lorenzo,
> >
> > I can avoid adding the scan handler in acpi_indirectio.c by skipping the
> > child enumeration, like with this change in scan.c:
> >
> > +static const struct acpi_device_id indirect_io_hosts[] = {
> > +    {"HISI0191", 0},    /* HiSilicon LPC host */
> > +    {},
> > +};
> > +
> > +static bool acpi_is_indirect_io_slave(struct acpi_device *device)
> > +{
> 
> Why don't you put the table definition here?
> 
> > +    struct acpi_device *parent = dev->parent;
> > +
> > +    if (!parent || acpi_match_device_ids(parent, indirect_io_hosts))
> > +        return false;
> > +
> > +    return true;
> 
> return parent && !acpi_match_device_ids(parent, indirect_io_hosts);
> 
> > +}
> > +
> >  static bool acpi_is_serial_bus_slave(struct acpi_device *device)
> >  {
> >      struct list_head resource_list;
> >      bool is_serial_bus_slave = false;
> >
> > +    if (acpi_is_indirect_io_slave(device))
> > +        return true;
> > +
> >      /* Macs use device properties in lieu of _CRS resources */
> >
> >
> > This means I can move all this scan code into the LLDD.
> >
> > What do you think? Please let me know.
> 
> If Lorenzo agrees, that will be fine by me modulo the above remarks.

I agree and I thank you for accepting this in core ACPI code, I think
that's much cleaner than a driver specific scan hook.

It is a shame we do not have a generic identifier for such bus in ACPI
but that won't happen overnight anyway (if ever, I think a binding for
LPC in the ACPI specs is hard to justify).

Thank you,
Lorenzo