Re: [PATCH V6 02/13] pci, acpi: Provide generic way to assign bus domain number.

Tomasz Nowicki
2016-04-27T11:59:56Z

On 27.04.2016 04:26, Bjorn Helgaas wrote:
> On Fri, Apr 15, 2016 at 07:06:37PM +0200, Tomasz Nowicki wrote:
>> As we now have valid PCI host bridge device reference we can
>> introduce code that is going to find its bus domain number using
>> ACPI _SEG method.
>>
>> Note that _SEG method is optional, therefore _SEG absence means
>> that all PCI buses belong to domain 0.
>>
>> While at it, for the sake of code clarity we put ACPI and DT domain
>> assign methods into the corresponding helpers.
>>
>> Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
>> Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com>
>> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
>> Tested-by: Jeremy Linton <jeremy.linton@arm.com>
>> Tested-by: Duc Dang <dhdang@apm.com>
>> Tested-by: Dongdong Liu <liudongdong3@huawei.com>
>> Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
>> Tested-by: Graeme Gregory <graeme.gregory@linaro.org>
>> Tested-by: Sinan Kaya <okaya@codeaurora.org>
>> ---
>> drivers/acpi/pci_root.c | 18 ++++++++++++++++++
>> drivers/pci/pci.c | 11 +++++++++--
>> include/linux/pci-acpi.h | 2 ++
>> 3 files changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
>> index 4581e0e..d9a70c4 100644
>> --- a/drivers/acpi/pci_root.c
>> +++ b/drivers/acpi/pci_root.c
>> @@ -419,6 +419,24 @@ out:
>> }
>> EXPORT_SYMBOL(acpi_pci_osc_control_set);
>>
>> +int acpi_pci_bus_domain_nr(struct device *parent)
>> +{
>> + struct acpi_device *acpi_dev = to_acpi_device(parent);
>> + unsigned long long segment = 0;
>> + acpi_status status;
>> +
>> + /*
>> + * If _SEG method does not exist, following ACPI spec (6.5.6)
>> + * all PCI buses belong to domain 0.
>> + */
>> + status = acpi_evaluate_integer(acpi_dev->handle, METHOD_NAME__SEG, NULL,
>> + &segment);
>
> We already have code in acpi_pci_root_add() to evaluate _SEG. We
> don't want to evaluate it *twice*, do we?

Ideally we do not want.

The main intention here was to avoid using "void *sysdata" to retrieve
domain number. sysdata means something different for each architectures.
This would be common way for all arch using PCI_DOMAINS_GENERIC option
such as ARM64.

>
> I was sort of expecting that if you added it here, we'd remove the
> existing call, but it looks like you're keeping both?

I leave _SEG evaluation in acpi_pci_root_add to keep support for IA64
and x86 which are still using arch-specific sysdata (struct
pci_sysdata->domain for x86 and struct pci_controller->segment for IA64)
to retrieve domain number.

ARM64 uses PCI_DOMAINS_GENERIC for DT boot method, it would be
consistent to keep it for ACPI too.

I am open to suggestions, do you think we should use sysdata for ARM64?

Thanks,
Tomasz