Date:	Fri, 24 Jan 2014 16:36:21 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Yijing Wang <wangyijing@...wei.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Dave Airlie <airlied@...hat.com>,
	Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [PATCH v5] ACPI: Fix acpi_evaluate_object() return value check

On Friday, January 24, 2014 07:54:29 AM Bjorn Helgaas wrote:
> On Thu, Jan 23, 2014 at 5:33 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Thursday, January 23, 2014 11:21:01 AM Bjorn Helgaas wrote:
> >> On Wed, Jan 22, 2014 at 8:42 PM, Yijing Wang <wangyijing@...wei.com> wrote:
> >> > Since acpi_evaluate_object() returns acpi_status and not plain int,
> >> > ACPI_FAILURE() should be used for checking its return value. Also
> >> > add some detailed debug info when acpi_evaluate_object() failed.
> >> >
> >> > Reviewed-by: Jani Nikula <jani.nikula@...el.com>
> >> > Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> >> > Signed-off-by: Yijing Wang <wangyijing@...wei.com>
> >> > ---
> >> > v4->v5: Add some detailed debug info for acpi_evaluate_object()
> >> >         failure suggested by Bjorn.
> >> > v3->v4: Fix spell error, add Jani Nikula reviewed-by.
> >> > v2->v3: Fix compile error pointed out by Hanjun.
> >> > v1->v2: Add CC to related subsystem MAINTAINERS
> >> > ---
> >> >  drivers/gpu/drm/i915/intel_acpi.c              |   33 ++++++++++++++++-------
> >> >  drivers/gpu/drm/nouveau/core/subdev/mxm/base.c |   13 ++++++---
> >> >  drivers/gpu/drm/nouveau/nouveau_acpi.c         |   25 +++++++++++-------
> >> >  drivers/pci/pci-label.c                        |   10 +++++--
> >> >  4 files changed, 54 insertions(+), 27 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/intel_acpi.c b/drivers/gpu/drm/i915/intel_acpi.c
> >> > index dfff090..e7b526b 100644
> >> > --- a/drivers/gpu/drm/i915/intel_acpi.c
> >> > +++ b/drivers/gpu/drm/i915/intel_acpi.c
> >> > @@ -31,11 +31,13 @@ static const u8 intel_dsm_guid[] = {
> >> >  static int intel_dsm(acpi_handle handle, int func)
> >> >  {
> >> >         struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
> >> > +       struct acpi_buffer string = { ACPI_ALLOCATE_BUFFER, NULL };
> >> >         struct acpi_object_list input;
> >> >         union acpi_object params[4];
> >> >         union acpi_object *obj;
> >> >         u32 result;
> >> > -       int ret = 0;
> >> > +       acpi_status status;
> >> > +       int ret;
> >> >
> >> >         input.count = 4;
> >> >         input.pointer = params;
> >> > @@ -50,10 +52,14 @@ static int intel_dsm(acpi_handle handle, int func)
> >> >         params[3].package.count = 0;
> >> >         params[3].package.elements = NULL;
> >> >
> >> > -       ret = acpi_evaluate_object(handle, "_DSM", &input, &output);
> >> > -       if (ret) {
> >> > -               DRM_DEBUG_DRIVER("failed to evaluate _DSM: %d\n", ret);
> >> > -               return ret;
> >> > +       status = acpi_evaluate_object(handle, "_DSM", &input, &output);
> >> > +       if (ACPI_FAILURE(status)) {
> >> > +               acpi_get_name(handle, ACPI_FULL_PATHNAME, &string);
> >> > +               DRM_DEBUG_DRIVER(
> >> > +                       "failed to evaluate _DSM for %s, exit status %u\n",
> >> > +                       (char *)string.pointer, (unsigned int)status);
> >> > +               kfree(string.pointer);
> >> > +               return -EINVAL;
> >>
> >> I said "too bad there isn't an *easy* way" to include more
> >> information.  IMHO this is too ugly and error-prone to use
> >> consistently.  And if you are going to add more information, why did
> >> you only do it for some of the calls and not others?
> >>
> >> I considered adding a %p extension to print the pathname; I don't know
> >> if that's worthwhile or not.  I think it would be ideal if we had a
> >> struct device and could use dev_info(), and then a way to connect the
> >> struct device with an ACPI path, like maybe a dmesg note when we
> >> create the struct device corresponding to an ACPI Device node.
> >
> > Well, we can generally print something like that from pci_acpi_setup().
> >
> > What about the below?  Wouldn't it generate too much output on some systems?
> 
> Yeah, that probably would generate an awful lot of output.  I was just
> hoping to avoid treating ACPI pathnames as first-class objects.  What
> do you think about a %p extension?  I played with that once, but I
> seem to have lost the patch.

Well, it may be worth doing.  However, that information is readily available from
sysfs anyway, you only need to follow the firmware_node link in the PCI device's
sysfs directory and read the path attribute from there.  For example, on my
system:

$ cat /sys/devices/pci0000:00/0000:00:1c.4/0000:0b:00.0/firmware_node/path
\_SB_.PCI0.RP05.PXSX

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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