linux-kernel - Re: [PATCH 30/30] PCI: remove pci_get_bus_and

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Message-ID: <6a78596e-720a-80a2-9d96-dcc79a32f677@codeaurora.org>
Date:   Wed, 22 Nov 2017 00:55:48 -0500
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Timur Tabi <timur@...eaurora.org>, linux-pci@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 30/30] PCI: remove pci_get_bus_and_slot() function

On 11/22/2017 12:45 AM, Timur Tabi wrote:
> On 11/21/17 11:31 PM, Sinan Kaya wrote:
>> Use pci_get_domain_bus_and_slot() with a domain number of 0 where we can't
>> extract the domain number. Other places, use the actual domain number from
>> the device.
>>
>> Now that all users of pci_get_bus_and_slot() switched to
>> pci_get_domain_bus_and_slot(), it is now safe to remove this function.
> 
> This doesn't really eliminate pci_get_bus_and_slot(), because it doesn't force developers to support non-zero domains.  What's to stop a driver developer from doing this?
> 
> #define pci_get_bus_and_slot(b, d) pci_get_domain_bus_and_slot(0, b, d)
> 
> thereby completely ignoring what you're trying to do?
> 

Surely, the goal is not to eliminate all domain 0 users/assumptions but open the
path for flexibility over time. 

There are patches in this series where I hard-coded a value of 0 because domain
information was not available.

For places where domain number information is available, I extracted domain number
and added into pci_get_domain_bus_and_slot() call such as xen or bn drivers.

This will allow these drivers to be used with non-zero segment numbers. These
issues were missed until this refactoring took place.

pci_get_domain_bus_and_slot() function makes the developer think about where to
find the domain number as it is mandatory. 

I also double checked that all current users of pci_get_domain_bus_and_slot()
are actually extracting the domain number correctly along with the bus, device,
function.

The assumption at this point is for pci_get_bus_and_slot() usages to be caught
in code-review.

This is a best-effort approach towards flexibility.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.