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

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Date:	Wed, 27 Apr 2016 13:59:30 +0200
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	arnd@...db.de, will.deacon@....com, catalin.marinas@....com,
	rafael@...nel.org, hanjun.guo@...aro.org,
	Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
	jiang.liu@...ux.intel.com, jchandra@...adcom.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....com, ddaney@...iumnetworks.com,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jcm@...hat.com
Subject: Re: [PATCH V6 02/13] pci, acpi: Provide generic way to assign bus
 domain number.

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@...ihalf.com>
>> Reviewed-by: Liviu Dudau <Liviu.Dudau@....com>
>> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
>> Tested-by: Jeremy Linton <jeremy.linton@....com>
>> Tested-by: Duc Dang <dhdang@....com>
>> Tested-by: Dongdong Liu <liudongdong3@...wei.com>
>> Tested-by: Hanjun Guo <hanjun.guo@...aro.org>
>> Tested-by: Graeme Gregory <graeme.gregory@...aro.org>
>> Tested-by: Sinan Kaya <okaya@...eaurora.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