linux-kernel - Re: About the "__refdata" tag in pci-keystone.c

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Date:   Mon, 27 Sep 2021 10:31:28 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Sergio M. Iglesias" <sergio@...y.xyz>
Cc:     bhelgaas@...gle.com, lorenzo.pieralisi@....com, robh@...nel.org,
        kw@...ux.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: About the "__refdata" tag in pci-keystone.c

On Mon, Sep 27, 2021 at 12:33:21PM +0200, Sergio M. Iglesias wrote:
> Hello!
> 
> I have checked the "__refdata" tag that appears in the file
> "drivers/pci/controller/dwc/pci-keystone.c" and it is needed. The tag has
> been there since the creation of the file on commit 6e0832fa432e and
> nothing has changed since that would make it redundant.
> 
> The reason it is needed is because the struct references "ks_pcie_probe",
> which is a function tagged as "__init", so the compiler will most likely
> complain about the "__refdata" being removed.
> 
> Should I send a patch to add a comment explaining why it is a necessary
> tag as recommended in "include/linux/init.h"?
> > [...] so optimally document why the __ref is needed and why it's OK).

Thanks a lot for looking into this.

I'm not yet convinced that either the __init or the __refdata is
necessary.  If there is a reason, it would not be "to silence a
compiler complaint"; it would be something like "the keystone platform
is different from all the other platforms because the other platforms
support X but keystone does not."

Also, there are a couple other .probe() functions that are marked
__init:

  $ git grep "static int .*_pci.*_probe" drivers/pci | grep __init
  drivers/pci/controller/dwc/pci-keystone.c:static int __init ks_pcie_probe(struct platform_device *pdev)
  drivers/pci/controller/dwc/pci-layerscape-ep.c:static int __init ls_pcie_ep_probe(struct platform_device *pdev)
  drivers/pci/controller/mobiveil/pcie-layerscape-gen4.c:static int __init ls_pcie_g4_probe(struct platform_device *pdev)
  drivers/pci/controller/pci-ixp4xx.c:static int __init ixp4xx_pci_probe(struct platform_device *pdev)

and their platform_driver structs are not marked __refdata:

  $ git grep "static struct platform_driver" drivers/pci | grep __refdata
  drivers/pci/controller/dwc/pci-keystone.c:static struct platform_driver ks_pcie_driver __refdata = {

I think this should all be more consistent: either all these __init
and __refdata annotations should be removed, or they should be used by
many more drivers.

Bjorn