linux-kernel - Re: [PATCH v3 21/32] powerpc: include default ioremap

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Date:   Tue, 11 Apr 2017 23:38:48 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-pci@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH v3 21/32] powerpc: include default ioremap_nopost()
 implementation

On Tue, 2017-04-11 at 13:29 +0100, Lorenzo Pieralisi wrote:
> The PCI specifications (Rev 3.0, 3.2.5 "Transaction Ordering and Posting")
> mandate non-posted configuration transactions. As further highlighted in
> the PCIe specifications (4.0 - Rev0.3, "Ordering Considerations for the
> Enhanced Configuration Access Mechanism"), through ECAM and
> ECAM-derivative configuration mechanism, the memory mapped transactions
> from the host CPU into Configuration Requests on the PCI express fabric
> may create ordering problems for software because writes to memory
> address are typically posted transactions (unless the architecture can
> enforce through virtual address mapping non-posted write transactions
> behaviour) but writes to Configuration Space are not posted on the PCI
> express fabric.
> 
> Include the asm-generic ioremap_nopost() implementation (currently
> falling back to ioremap_nocache()) to provide a non-posted writes
> ioremap interface to kernel subsystems.

NAK. As explained in my reply to patch 0.

> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Cc: Michael Ellerman <mpe@...erman.id.au>
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > Cc: Paul Mackerras <paulus@...ba.org>
> ---
>  arch/powerpc/include/asm/io.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h
> index 5ed2924..6dcd0e2 100644
> --- a/arch/powerpc/include/asm/io.h
> +++ b/arch/powerpc/include/asm/io.h
> @@ -757,6 +757,7 @@ extern void __iomem *ioremap_prot(phys_addr_t address, unsigned long size,
>  extern void __iomem *ioremap_wc(phys_addr_t address, unsigned long size);
> >  #define ioremap_nocache(addr, size)	ioremap((addr), (size))
> >  #define ioremap_uc(addr, size)		ioremap((addr), (size))
> +#include <asm-generic/ioremap-nopost.h>
>  
>  extern void iounmap(volatile void __iomem *addr);
>