linux-kernel - Re: [PATCH v2 07/22] PCI: ECAM: use ioremap

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Date:   Thu, 30 Mar 2017 17:20:16 +0100
From:   Will Deacon <will.deacon@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Pratyush Anand <pratyush.anand@...il.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Mingkai Hu <mingkai.hu@...escale.com>,
        John Garry <john.garry@...wei.com>,
        Tanmay Inamdar <tinamdar@....com>,
        Murali Karicheri <m-karicheri2@...com>,
        Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        Ray Jui <rjui@...adcom.com>,
        Wenrui Li <wenrui.li@...k-chips.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Minghuan Lian <minghuan.Lian@...escale.com>,
        Jon Mason <jonmason@...adcom.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Michal Simek <michal.simek@...inx.com>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Roy Zang <tie-fei.zang@...escale.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>
Subject: Re: [PATCH v2 07/22] PCI: ECAM: use ioremap_nopost() to map config
 region

On Mon, Mar 27, 2017 at 10:49:35AM +0100, Lorenzo Pieralisi wrote:
> Current ECAM kernel implementation uses ioremap() to map the ECAM
> configuration space memory region; this is not safe in that on some
> architectures the ioremap interface provides mappings that allow posted
> write transactions. This, as highlighted in the PCIe specifications
> (4.0 - Rev0.3, "Ordering Considerations for the Enhanced Configuration
> Address Mechanism"), can create ordering issues for software because
> posted writes transactions on the CPU host bus are non posted in the
> PCI express fabric.
> 
> Update the ioremap() interface to use ioremap_nopost() whose
> mapping attributes guarantee that non-posted writes transactions
> are issued for memory writes within the ECAM memory mapped address
> region.
> 
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/ecam.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Acked-by: Will Deacon <will.deacon@....com>

Will