linux-kernel - Re: [PATCH 02/20] PCI: fix pci_remap

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Message-ID: <20170320161933.GD7632@red-moon>
Date:   Mon, 20 Mar 2017 16:19:33 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Liviu Dudau <liviu@...au.co.uk>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Liviu Dudau <Liviu.Dudau@....com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Wenrui Li <wenrui.li@...k-chips.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Will Deacon <will.deacon@....com>,
        Michal Simek <michal.simek@...inx.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Tanmay Inamdar <tinamdar@....com>, linux-arch@...r.kernel.org,
        Pratyush Anand <pratyush.anand@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Jon Mason <jonmason@...adcom.com>,
        Murali Karicheri <m-karicheri2@...com>,
        Arnd Bergmann <arnd@...db.de>,
        Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        Ray Jui <rjui@...adcom.com>,
        John Garry <john.garry@...wei.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mingkai Hu <mingkai.hu@...escale.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Jingoo Han <jingoohan1@...il.com>,
        linux-kernel@...r.kernel.org,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Minghuan Lian <minghuan.Lian@...escale.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Roy Zang <tie-fei.zang@...escale.com>
Subject: Re: [PATCH 02/20] PCI: fix pci_remap_iospace() remap attribute

On Fri, Mar 17, 2017 at 05:26:18PM +0100, Luis R. Rodriguez wrote:
> On Fri, Mar 17, 2017 at 10:43:39AM +0000, Liviu Dudau wrote:
> > On Fri, Mar 17, 2017 at 01:33:21AM +0100, Luis R. Rodriguez wrote:
> > > a) should we then use a Fixes tag for this patch ?
> > 
> > I'm not aware of issues being reported, but Lorenzo might have more info on this.
> 
> Lorenzo ? If not what exactly made you discover this ? If it is a fix, and only 
> ARM64 is implicated, seems like a worthy change to consider for stable for the
> sake of stable ARM64 kernels. But, that would leave the PCI config space without
> a simple 1 liner fix too -- so maybe its not worth it. Distributions wanting
> to support ARM64 however would like to carry these changes, so some annotations
> such as Fixes should help.

It started with this thread:

http://lists.infradead.org/pipermail/linux-arm-kernel/2017-January/477353.html

this series is not fixing any current issue I am aware of (but I am not
keen on leaving code as-is either) hence adding a Fixes: tag is problematic.

I would leave stable kernels alone for the time being.

Lorenzo

> > > b) it does not seem clear what the semantics for pgprot_device() or even
> > >    pgprot_noncached(). Can you add some ?
> > > 
> > > 8b921acfeffdb ("PCI: Add pci_remap_iospace() to map bus I/O resources")
> > > 
> > > Also this patch claims archs can override this call alone, as its __weak.
> > > So is the right thing to do to change pci_remap_iospace() to pgprot_noncached()
> > > or is it for archs to add their own pci_remap_iospace()? If so why ? Without
> > > proper semantics defined for these helpers this is all fuzzy.
> > 
> > That was the initial intention, to let arches / platforms overwrite the whole
> > pci_remap_iospace(). I guess the reality is that no one needs to overwrite it except
> > for the AArch64 quirk, so probably easier to remove the __weak and fix the attributes for arm64.
> 
> Sounds much more reasonable to me.
> 
>   Luis