On Thursday, August 05, 2010, Hidetoshi Seto wrote:
> (2010/08/05 8:51), Rafael J. Wysocki wrote:
> > On Wednesday, August 04, 2010, Rafael J. Wysocki wrote:
> >> On Wednesday, August 04, 2010, Hidetoshi Seto wrote:
> >>> (2010/08/04 14:46), Kenji Kaneshige wrote:
> >>>> (2010/08/04 6:02), Rafael J. Wysocki wrote:
> >>>>> On Tuesday, August 03, 2010, Rafael J. Wysocki wrote:
> >>>>>> On Tuesday, August 03, 2010, Hidetoshi Seto wrote:
> >>>>>>> (2010/08/03 13:52), Kenji Kaneshige wrote:
> >>>>>>>> (2010/08/03 6:59), Rafael J. Wysocki wrote:
> >>>>>>>>> @@ -434,19 +432,6 @@ acpi_status acpi_pci_osc_control_set(acp
> >>>>>>>>> if ((root->osc_control_set& control_req) == control_req)
> >>>>>>>>> goto out;
> >>>>>>>>>
> >>>>>>>>> - /* Need to query controls first before requesting them */
> >>>>>>>>> - if (!root->osc_queried) {
> >>>>>>>>> - status = acpi_pci_query_osc(root, root->osc_support_set, NULL);
> >>>>>>>>> - if (ACPI_FAILURE(status))
> >>>>>>>>> - goto out;
> >>>>>>>>> - }
> >>>>>>>>> - if ((root->osc_control_qry& control_req) != control_req) {
> >>>>>>>>> - printk(KERN_DEBUG
> >>>>>>>>> - "Firmware did not grant requested _OSC control\n");
> >>>>>>>>> - status = AE_SUPPORT;
> >>>>>>>>> - goto out;
> >>>>>>>>> - }
> >>>>>>>>
> >>>>>>>> I think acpi_pci_osc_control_set() still need to query before commit
> >>>>>>>> to ensure all the requested controls are granted to OS.
> >>>>>>>>
> >>>>>>>> So the code needs to be
> >>>>>>>>
> >>>>>>>> status = acpi_pci_query_osc(root, root->osc_support_set,&control_req);
> >>>>>>>> if (ACPI_FAILURE(status))
> >>>>>>>> goto out;
> >>>>>>>
> >>>>
> >>>> Sorry, that should have been
> >>>>
> >>>> query = control_req;
> >>>> status = acpi_pci_query_osc(root, root->osc_support_set, &query);
> >>>> if (ACPI_FAILURE(status))
> >>>> goto out;
> >>>> if ((query & control_req) != control_req) {
> >>>> printk_(KERN_DEBUG
> >>>> "Firmware did not grant requested _OSC control\n");
> >>>> status = AE_SUPPORT;
> >>>> goto out;
> >>>> }
> >>>>
> >>>> I know current pcie_port_acpi_setup() queries the requesting controls
> >>>> before acpi_pci_osc_control_set() and only one control is requested
> >>>> in the other code. However, I think acpi_pci_osc_control_set() still
> >>>> need to query the requested controls to ensure all the requested
> >>>> controls, in case someone calls this function without querying the
> >>>> requesting controls. In other words, I think it must be ensured that
> >>>> any controls are never granted to OS when acpi_pci_osc_control_set()
> >>>> returns error.
> >>>
> >>> I think the following patch is what you mean.
> >>>
> >>> And... (Continue to next post)
> >>>
> >>> Thanks,
> >>> H.Seto
> >>
> >> OK, I'll repalce my 7/8 with the patch below.
> >
> > Actually, having reconsidered that, I don't think this approach is valid.
> >
> > First, it has the problem that if acpi_pci_osc_control_set() returns error
> > code, the caller doesn't really know whether the query failed, or the final
> > request failed. Arguably, it won't matter for the majority of callers, but
> > some of them might be interested in knowing that in principle.
>
> Ugh... there are only 2 callers now and both of them are in the majority.
> I don't think it is a time to take care of an invisible minority who might
> require acpi_pci_osc_raw() to complete its work.
>
> >
> > Second, the callers that call acpi_pci_osc_control_query() before
> > acpi_pci_osc_control_set() don't need the additional query inside
> > of acpi_pci_osc_control_set().
>
> So we can recommend all of callers not to call acpi_pci_osc_control_query()
> before acpi_pci_osc_control_set().
Please consider pcie_port_acpi_setup() in [4/8].
It has to do the query by itself, because it may not request the controls
_even_ _if_ _the_ _query_ _is_ _successful_. Namely, if the result of the
query is that the BIOS won't let us control the PCIe Capability Structure,
pcie_port_acpi_setup() should return error code instead of requesting control
of the other features. Now, if you put the query into
acpi_pci_osc_control_set(), it won't be able to recognize this corner case and
handle it correctly.
> I suppose that almost all of "the majority" just want to set fixed set of
> controls and they will just return error when fails anyway.
>
> >
> > Therefore I'd prefer to have two separate functions, one for querying and the
> > other for requesting control. Then, we can provide a helper that calls the
> > both of them for the callers of acpi_pci_osc_control_set() that don't need
> > to call acpi_pci_osc_control_query() directly by themselves.
>
> I'm afraid the "two" is not enough for the minority.
>
> Therefore I don't think it is a time to prepare for such an inexistent
> minor usage.
As explained above, I think there is a reason to do that, because
pcie_port_acpi_setup() has to run a query anyway.
> > Given that acpi_pci_osc_control_query() is introduced by
> > https://patchwork.kernel.org/patch/117176/ , the helper may be implemented
> > like in the appended patch.
> >
> > After that patch, the $subject patch can be applied without any modifications
> > to remove the no-longer-used fields in struct acpi_pci_root.
> >
> > ---
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> > Subject: ACPI / PCI: Introduce function for requesting _OSC controls safely
> >
> > Calling raw acpi_pci_osc_control_set() is generally unsafe, because
> > it may return error code even if control of some requested features
> > have been granted by the BIOS. For this reason the callers of
> > acpi_pci_osc_control_set() should call acpi_pci_osc_control_query()
> > before it to make sure that the BIOS is willing to grant control of
> > the requested features.
> >
> > Introduce helper function acpi_pci_osc_control_set_safe() allowing
> > a caller of acpi_pci_osc_control_set() who is not interested in
> > the control bits returned by acpi_pci_osc_control_query() to
> > request control of _OSC features in a safe way.
> >
> > Make acpi_get_hp_hw_control_from_firmware() use the new function.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> > ---
> > drivers/acpi/pci_root.c | 24 ++++++++++++++++++++++++
> > drivers/pci/hotplug/acpi_pcihp.c | 2 +-
> > include/linux/acpi.h | 1 +
> > 3 files changed, 26 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/drivers/acpi/pci_root.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/acpi/pci_root.c
> > +++ linux-2.6/drivers/acpi/pci_root.c
> > @@ -472,6 +472,30 @@ out:
> > }
> > EXPORT_SYMBOL(acpi_pci_osc_control_set);
> >
> > +/**
> > + * acpi_pci_osc_control_set_safe - Query and set _OSC control bit mask.
> > + * @handle: ACPI handle of a PCI root bridge (or PCIe Root Complex).
> > + * @flags: Mask of _OSC bits to query and set.
> > + *
> > + * Check if the BIOS is willing to grant control of the features represented
> > + * by @flags and request control of these features from it.
> > + **/
> > +acpi_status acpi_pci_osc_control_set_safe(acpi_handle handle, u32 flags)
> > +{
> > + acpi_status status;
> > + u32 ctrl = flags;
> > +
> > + status = acpi_pci_osc_control_query(handle, &flags);
> > + if (ACPI_FAILURE(status))
> > + return status;
> > + if ((ctrl & flags) != ctrl)
> > + return AE_SUPPORT;
> > +
> > + status = acpi_pci_osc_control_set(handle, flags);
> > + return status;
> > +}
> > +EXPORT_SYMBOL(acpi_pci_osc_control_set_safe);
> > +
> > static int __devinit acpi_pci_root_add(struct acpi_device *device)
> > {
> > unsigned long long segment, bus;
> > Index: linux-2.6/drivers/pci/hotplug/acpi_pcihp.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/pci/hotplug/acpi_pcihp.c
> > +++ linux-2.6/drivers/pci/hotplug/acpi_pcihp.c
> > @@ -358,7 +358,7 @@ int acpi_get_hp_hw_control_from_firmware
> > acpi_get_name(handle, ACPI_FULL_PATHNAME, &string);
> > dbg("Trying to get hotplug control for %s\n",
> > (char *)string.pointer);
> > - status = acpi_pci_osc_control_set(handle, flags);
> > + status = acpi_pci_osc_control_set_safe(handle, flags);
> > if (ACPI_SUCCESS(status))
> > goto got_one;
> > if (status == AE_SUPPORT)
> > Index: linux-2.6/include/linux/acpi.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/acpi.h
> > +++ linux-2.6/include/linux/acpi.h
> > @@ -307,6 +307,7 @@ acpi_status acpi_run_osc(acpi_handle han
> >
> > extern acpi_status acpi_pci_osc_control_query(acpi_handle handle, u32 *mask);
> > extern acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 flags);
> > +extern acpi_status acpi_pci_osc_control_set_safe(acpi_handle handle, u32 flags);
> > extern void acpi_early_init(void);
> >
> > #else /* !CONFIG_ACPI */
> >
> >
>
> So I'd like to say NAK against this patch, sorry.
IMHO you've not given a sufficient reason for that.
Thanks,
Rafael
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